Last updated 

December 

2002 

Surge Protection Anthology 

All Papers – Part 8 

Coordination of cascaded surge-protective devices 

Surg

Happe

FOREWORD 

The papers included in this part of the Anthology provide basic and tutorial information on 

coordination of the so-called “Cascaded SPDs” in the context of low-voltage AC power circu

As presented in this part of the anthology, the subject was approached by a combination 

experiments and theoretical considerations. Interest in the subject arose in the early sevent

following the introduction of metal-oxide varistors (Phase 1 papers). 

With the concept of “whole house protection” that emerged in the nineties, a new se

experiments and numerical simulations focused on issues raised by industry’s choice of offe

very low limiting voltages for plug-in SPDs, which made effective coordination more diffic

Concurrently, more attention was given to the rare but possible scenario of a direct lightn

flash to a building, raising the threat level to new heights not only for SPDs installed at 

service entrance, but also for downstream equipment, in particular those SPDs with low limi

voltage rating such as plug-in TVSSs (Phase 2 papers). 

Industry interest in the matter grew, and resulted in many publications, as shown by the pap

contributed by the researchers cited in Annex A. For obvious copyright limitations, the pap

from other researchers cannot be reprinted here. The pre-1985 papers in this Part 8 w

copyrighted by the IEEE, or were proprietary to the General Electric Company; both gracio

gave permission for reprinting in this anthology. The post-1985 papers, written thanks to 

support from EPRI PEAC and the National Institute of Standards and Technology, are in 

public domain. 

The information contained in these papers was based on experiments as well as numer

simulations, and were presented at different forums, in the context of different audiences, bu

on the theme that effective coordination of devices requires coordination of the specifications

particular if the devices are provided by different entities. 

CONTENTS 

Phase 1 papers 

Surge voltage suppression in residential power circuits (1976) 

Coordination of overvoltage protection in low-voltage residential systems (1978) 

Coordination of surge protectors in low-voltage AC power circuits (1980) 

The coordination of surge protectors in low-voltage AC power circuits (1980) 

Phase 2 papers

Cascading surge-protective devices: Coordination versus the IEC 664 staircase (1991

Cascading surge-protective devices: Options for effective implementations (1992) 

Coordinating cascaded surge-protective devices: Hi-Low versus Low-High (1993) 

Gapped arresters revisited: A solution to cascade coordination (1998) 

The role and stress of surge-protective devices in sharing lightning current (2002) 

Annotated Bibliography – Application of surge-protective devices and coordination 

 of cascades (1992) 
SURGE

VOLTAGE

SUPPRESSION

IN

RESIDENTIAL

POWER

CIRCUITS
Significance:

Part 4 – Propagation and coupling of surges

Part 7 – Mitigation techniques

Part 8 – Coordination of cascaded SPDs

Laboratory tests on the effect of distance for coordination between a surge-protective device (SPD) at the service

entrance and an SPD at the end of a branch circuit.

The service entrance SPD, 1960-1970 vintage, consisted of a silicon carbide disc with a series gap.

The branch circuit SPD consisted of a simple MOV disc incorporated in a modified plug-and-receptacle combination

probably the first attempt at packaging an MOV for residential surge protection.

Tests were performed with a simple generator capable of delivering up to 8 kV peak open-circuit voltage of 2/60 :s

waveform and 2 kA peak short-circuit current of 30/50 :s waveform. These values – dating back to pre-IEEE 587

consensus waveforms – were at the time deemed to represent a severe surge associated with a lightning flash to the

power system, outside of the residence.

One objective of the tests was to determine the values of surge current and distance between SPDs that produced

the threshold from no sparkover of the service entrance SPD (maximum stress on the MOV) to sparkover, thus

limiting the stress on the MOV. This was one of the first illustrations of what became a series of experimental and

theoretical studies of the “cascade coordination” concept.

Filename: Coordination 1976
4UTHOR SUBJECT NO 

surge voltage Martzloff, FD 76CRD092 

suppression %$ay 1976 llTLE GE CLASS 

Surge Voltage Suppression in Residential 1 

Power Circuits NO.PAGES 11 

GENERAL ELECTRIC 

General Electric Company 

Corporate Research and Development 

Schenectady, New York 

I j,R:i:,":r' Electronic Power Conditioning CORPORATE RESEPRCH AND DEVELOPMEN1 

and Control Laboratory SCHENECTAOY, N.Y. 

TECHnlCAL lNFORMATlO

SERIES 

WMMARY Tests performed on a representative residential 

wiring system with a Home Lightning Protector (HLP) and 

a Voltage Spike Protector (VSP) installed on the service 

box and an outlet, respectively, indicate good coordinatior 

between the characteristics of the two devices. For surgt 

of relatively small amplitude, the VSP performs all of the 

voltage clamping functions. As the energy (current) of tht 

surge increases, a point is reached where the HLP sparkmer voltage is reached, and this device takes over the 

[unction of diverting the surge energy while the VSP keeps 

the voltage clamped at low levels. The current for which 

this transfer takes place depends on the distance between 

the two devices. For practical situations, enough distance 

[wiring length) will exist to limit the duty imposed on the 

VSP to acceptable levels, giving the HLP an opportunity 

to divert high energy surges. 

transients, spikes, lightning, arrestors, 

varistors, GE-MOV 

INFORMATION PREPARED FOR 

Additional Hard Copies Available From 

Microfiche Copies Available From 

RD-54 (1W70) 

Corporate Research 8 Development Distrib

P.O. Box 43 Bldg 5 , Schenectady , N.Y.

Technical Information Exchange 

P.O. Box 43 Bldg. 5, Schenectady , N.Y.
SURGE VOLTAGE SUPPRESSION 

IN RESIDENTIAL POWER CIRCUITS 

- F.D. Martzloff - 

Surge voltages occurring in residcntial power circuits have two origins: 

external surges, produccd by power system 

switching operation or by lightning, and 

internal surgcs produccd by switching of 

appliances in thc home. The voltage levels 

of these surgcs are sufficient to cause 

failure of sensitive electronic appliances, 

and some of thc highcr surges can even fail 

the morc rugged clcctromechanical devices 

(clocks, motors and heater^)^,^. 

For many years, the General Electric 

Company has offered a secondary surge 

arrester under the name of "Home Lightning 

Protector" (HLP), which is very effective 

in protecting non-electronic devices 

againsL high energy, high voltage surges 

associated wi Lh lightning or power syst.em 

swiLching. Huweve1-, the protective level 

of this arrester, consistent with the 

limitations imposed by the design of such 

a device, is still too high for sensitive 

el ecti-onic devices. Furthermore, its installation requires a competent electrician 

A new suppressor has been developed 

and introduced by the Wiring Uevicc Dcpartment under the name "Voltage Spike Protector" (VSP); this device incorporates a 

GE-MOW varistor in a plug-in device allowing purchase and easy installation by the 

user. The protective level of this device 

is substantially lower (that is, betLer 

protection is provided) than the HLP, so 

that protecLior~ 01 ..ensi Live electrnni c 

appliances is now possible. Howr-ver , the 

energy handling capabiliLy of this 

suppressor is lower than Lhat of Lhe HLP, 

so thaL large currents assoi: iated wi th 

lightning slrikes cannot 1~e handled by the 

device. 

The availability of these two different types of suppressors now makes it 

possible to obtain a coordinated protection 

of all the appliances in a home. Installation of the IILP at the service entrance 

will deal with the larger surges, while the 

VSP installed at a wall receptacle will 

protect the more sensitive dcviccs. For 

the lower surges, the VSP will clamp the 

voltage to a low level. For the higher 

surges, the VSP will first attempt to absorb all the surgc current, but the voltage 

developcd across the varistor plus the voltage drop in the wiring between the receptacle whcrc the VSP is installed and the 

servic.e box where the HLP is installed 

reach the sparkover voltage of the HLP

The RLP then takes over, diverting the 

current surgc trom thc VSP, so that no 

cessive cncrgy is applied to the latte

This report describes how this co

dination takes place, based on simula

surges in a representative wiring syst

The lcvels of voltage and current in t

tests show when the HLP and VSP respec

assume all of the protective function

where the transfer takes place, depend

on the distance between Lhe VSP in an 

and the service box where the HLP is i

stalled. 

11, THE HOME LIGHTNING PROTECTOR 

The Home Lightning Protector (HL

produced by the Distribution Transform

Business Departmcnt. It is a surge a

of the valve and series gap type (Fig

Earlier designs involved lead oxide p

with the oxide pellet acting as a non

resistor and the multiple contact poi

between the pellets as a multiple gap

more recent design uses a Thyrite@ di

series with a low voltage gap. 

This UL-listed arrester is rated 

lighLning surge duty, and is describe

the GE Handbook as having a sparkover 

2 kV crest under a 10 kV/l~s impulse w

discharge voltages of 1, 1.2 and 1.4 

respec.tive1 y at 1500, 5000 and 10,000 

a 10 x 20 vs current wave (see Append

O RrgisLrred trademark of the General Electric 

C~~rnpdny. 

Figure 1. Home Lightning Protec

hlanuscript received May 3, 1976. 
As any gap-type arrester will, the HLP 

has a volt-time characteristic exhibiting 

some increase in the sparkover voltage as the rate of rise of the impinging surge increases. Typical sparkover voltages for 

the sample tested under the particular waveform used here were in the order of 2000 V 

or less. This represents an effective 

clamping to protect electromechanical appliances, heaters, etc. However, sensitive 

electronic appliances may well have failure 

levels below 2000 V. This is recognized in 

the box label which describes the HLP. as a protector for "home and farm non-electronic 

equipment, wiring appliances and water 

heaters". 

Thus, while the HLP offers reliable 

protection for non-electronic appliances 

and a respectable energy handling capability, a device with a lower voltage clamping characteristic is required to protect 

sensitive electronics. This need is now met through the Voltage Spike Protector, 

described in the next section. 

I1 I THE VOLTAGE SPIKE PROTECTOR 

The heart of this device is a GE-MOVB 

varistor, connected line-to-line in a com- bination plug-socket (Fig. 2). This package, developed and produced by the Wiring 

Devices Department, makes ~t convenient for 

the user to install the protector at any 

outlet in the house, and the socket end 

allows the user to plug the protected appliance directly into the protector. In fact, 

protection is afforded to devices in all 

other wall outlets (to a varying degree, 

depending on the branch circuit configuration) and it is not mandatory to plug the 

appliance into the suppressor (it is a 

shunt, not a series device). One of the reasons for the socket end is just a convenience, so as not to lose the use of a receptacle or require a cube tap. 

Figure 2. Voltage Spike Protector 

In addition to the varistor, a n

resettable, one-shot thermal protecti

inserted in series with the varistor

insurance against thermal runaway of 

varistor in case of excessive environ

conditions. 

The protective characteristics o

varistor are such that a 15 A surge, 

cal of large internally-generated sur

will limit the voltage across the sup

to 500 V, as opposed to values exceed

2000 V which have been recorded durin

monitoring of houses known to contain 

switching device producing such surg

For large current values such as thos

ciated with "lightning remnants", i.e

surge entering the house when a ligh

stroke occurs near the house (but not 

direct stroke), one can expect curren

the order of 1000 to 2000 A. These w

produce a voltage of 800 to 1000 V ac

the varistor. However, as we will se

presence of an HLP device at the serv

box, ahead of the varistor, will limi

current flowing toward the varistor t

lower value, by diverting the current 

through the HLP because of the additi

drop in the wire which raises the vol

across the HLP to its sparkover volta

IV, TEST CIRCUIT 

The test circuit (Fig. 3) consis

a terminal board from which two line

25 ft. (7.5 m) and the other 100 ft. 

long were strung in the test area. A 

10 ft. (3 m) line simulated the servi

drop. All of these were made of 3-co

non-metallic sheath wire (Etcoflex ty

#12 AWG. The neutral and the ground 

of the three lines were connected tog

at the terminal board, and thence to 

reference ground of the test circuit

All surge currents were applied 

ween the line conductor (black) at th

of the service drop and the reference 

ground. These impulses were obtained 

a 5 UF capacitor, charged at a suitab

voltage, and discharged into the wiri

system by an ignitron switch. Figure 

shows the connections and parameters 

surge generator circuit. The resulta

open-circuit voltage waveform, a unid

tional wave of 1 us rise time x 50 ps 

1/2 value time, corresponds to the st

test wave in utility systems. It is 

more severe test than the recommended 

wave~hape~,~ and as such provides ver

servative results. Figure 5 shows ty

open-circuit voltage and short-circui

current waveforms. Voltages were rec

by a Tektronix 7633 storage oscillosc

through a P6015 attenuator probe (100

currents by a Tektronix 7633 oscillos

through a current probe P6042 with a 

1000:l current transformer. Thus, the 

brations displayed on the oscillogram 

to be multiplied by 1000 for the volt
GR~EN 

(GROUND) 

Figure 3. Test Circuit 

while the current traces show the 50 mV 

setting corresponding to the rated output 

of the current probe, with the ampere per 

division shown corresponding to the current 

transformer ratio and current probe input 

setting for a direct reading. Sweep rate 

is also shown on the oscillograms, at 10 us/ 

div. for all the tests. 

V, TEST RESULTS 

Several test conditions were investigated, with the varistor at the end of the 

short line or at the end of the long line. 

The HLP and VSP responses were established 

by connecting them one at a time, in addition to establishing the open-circuit voltage and short-circuit current for each 

HVDC 

CIRCUIT 

- - - - 

Figure 4. PuZse Generator Circ

condition. The results will be disc

with reference to specific sets of o

grams showing voltages and currents 

various parts of the circuit, each t

the same setting of the surge gener

1. HLP AND VSP RESPONSE 

Figure 5a shows a 3000 V open-

voltage surge at the service box, w

neither suppressor connected. Figu

shows the corresponding 600 A short

current for a jumper connected at th

service box. Figure 6a shows the v

across the HLP when subjected to the 

defined by Figures 5a and 5b. Note 

the sparkover voltage reaches 2200 V 

several oscillations before the volt

settles down to the impulse discharg

voltage at about 1000 V at its star

(a) Figure 5 (b l 

Open Circuit Voltage and Short-circuit Current 

(without any protector) 
(b) (c) 

Figure 6 

Response of HLP & VSP 

Figures 6b and 6c show respectively the 

voltage and current across the varistor. 

Note that the maximum voltage is 600 V, for 

a 550 A current on the varistor. (The 

current in the varistor is lower than the 

available short-circuit current because of 

the reduced available voltage since the 

varistor holds off 600. 

2. PROPAGATION OF SURGES 

Figure 7 shows several oscillograms 

indicating how the surge propagates in the 

wiring in the absence of any suppressor, 

and how the installation of one VSP device 

at an outlet is reflected elsewhere in the 

system. Figures 7a and 7b show respectively 

the open-circuit voltage an3 short-circuit 

current at the service box. At the openended 25 ft. (7.5 m) line, the voltage is 

substantially the same a s a t the box (Fig. 

7c). However, at the end of the 100 ft. 

(30 m) line with a 50 R termination, a 

significant decrease of the slope is noticeable, while the crest remains practically 

unchanged (Fig. 7d). 

In Figures 7e-g, a VSP varistor has 

been added at the end of the 25 ft (7.5 m) 

line. Voltage and current at the varistor 

are shown in Figures 7e and 7f, with a 

maximum voltage of 500 V for a 200 A surge. 

Meanwhile, the voltage at the box is limited 

to 750 V, an appreciable reduction from the 

1500 V that would exist without the remote 

VSP under this surge condition (Fig

3. TRANSFER OF SURGES 

With the voltage limiting at th

provided by the installation of a V

at a remote outlet (Fig. 7g), an HLP 

nected at the service box cannot rea

sparkover voltage until substantial 

currents are involved. For a short 

tance between the serkice box and th

a larger current will be required th

a greater distance. The value of th

rent required to reach sparkover as 

function of the distance is therefo

interest. 

For a distance of 25 ft. (7.5 m

threshold condition where sparkover 

HLP just occurs is depicted in Figu

In Figures 8a and 8b, the open-circu

tage and short-circuit current are 

for this threshold setting of the g

Inspection of the oscillograms show

open-circuit voltage of 8.1 kV and a 

circuit current of 1.9 kA, hence a c

lated sourcc impedance of 4.2 fi.* 

low value of the source impedance (c

* This is only a crude approximation since 

current waveform does not match the volt

waveform. Therefore, the circuit impeda

not a pure resistance or characteristic 
fa) open-circuit voZtage - at box 

(el open-circuit voZtage - 25 ft. 17.5m) 

(b 1 short-circuit current 

(d) open-circuit voltage - 100 ft

(el voZtage at VSP - 25 ft. 17.5m) (7) current in VSP - 25 ft. 1

(g) voZtage at box with VSP L? 25 ft. 17.5m) 

Figure 7 

Propagation of Surges 
to proposed valuesz> 3, provides a very conservative evaluation of the system performance. For the same setting as Figures 8a 

and 8b, the oscillograms of Figures 8c and 

8d show the case where the HLP has sparked 

over, as indicated by its voltage (8c) and 

current (8d) traces. In Figures 8e and Sf, 

the traces show the voltage (8e) and current 

(Sf) in the VSP for a case where the HLP did 

not spark over (due to the scatter of sparkover or a slight difference in the output of 

the surge generator). This case represents 

the most severe duty to which the VSP would 

be exposed, for a distance of 25 ft. (7.5m), 

and in reality is already likely to be an 

actual lightning stroke on the power system, 

rather than just a "lightning remnant" 

associated with a remote or indirect stroke. 

Figure Sf indicates a crest current of 1200A 

in the varistor, which just exceeds the 

published surge rating of the varistor, 

however, as an isolated occurrence, th

current level has been found acceptab

during laboratory tests. As stated ab

this level of current would be reached 

for direct strokes, and for a VSP con

fairly close to the service box. In a 

where there would be no HLP installed 

the box, but only the VSP installed a

outlet, the voltage rise in the wiring 

the meter coils would most likely res

a flashover of the system, which would 

divert the excessive energy away from 

VSP, just as the HLP did in the test. 

course, this diversion may take place 

undesirable manner, which is precisely 

the HLP is supposed to eliminate when 

stalled. On the other hand, the sale 

literature for the VSP also specifica

excludes direct lightning strokes from 

protective ability of the VSP. 

(a) open-circuit voltage 

fcl voltage at HLP when HLP does 

sparkover - VSP at 25 ft. 17.5~1) 

(el voltage at VSP when HLP does not 

sparkover - VSP at 25 f t. 17.5ml 

(bl short-circuit current 

current in HLP after sparkover - VSP at 25 ft. (7.5rnl 

current in VSP when HLP does not 

sparkover - VSP at 25 ft. 17. Sml 

Figure 8 

Transfer of Surge Conduction 
For greater distances between the VSP 

and the service box, the surge transfer will 

occur at lower current. For instance, with 

100 ft. (30m), the oscillograms of Figure 9 

document the transfer of the surge to the 

HLP at much lower current levels. Oper,.. 

circuit voltage and short-circuit current 

are indicated in Figures 9a and 9b as 

previously. With the VSP at 25 ft., only 

the VSP carries tLe surge as indicated in 

Figures 9c and 9d. However, with th

removed 100 ft. (30m) away from the 

the latter takes over for this lower 

able current (700 A) and relieves mo

the surge from the VSP, as indicated 

Figures 9e through 9h. The current 

in the VSP is now only 125 A (Fig. 9

500 A flowing in the HLP (Fig. 9h). 

corresponding voltage at the VSP and 

are shown in Figures 9e and 9%. 

'a) open-circuit voltage short-circuit current 

--- 

ii 1 VSP at 25 ft. (7.5m) - Voztaqe of VSP Id) VSP at 25 ft. (7.5m) - Current in V

(el VSP at 100 ft. (30m) - Voltage of VSP (f) VSP at 100 ft. (30m) - Current in V

(gl VSP at 100 ft. f30ml - Voltage of HLP (hi VSP at 100 ft. (30ml - Current in HL

Figure 9 

Transfer of Surges 
Further information is presented in 

Figure 10, with oscillagrams recorded at the 

same generator setting as in Figure 9. 

Figure 10c shows the voltage at the end of 

the 100 ft. (30m) line, between the line 

wire and the ground wire (not the ground 

reference, but the ground carried with the 

wire); likewise, Figure lob shows the voltage at the same point between the neutral 

wire and the ground wire, both oscillograms 

recorded with the HLP at the service box 

and the VSP at that line end. These voltages should be compared to the line-

(more precisely, line-to-neutral) vo

of only 500 V recorded for the same 

condition in Figure 9e. To check th

these voltages were not spurious rec

the oscillogram of Figure 10c was re

with the probe tip connected to its 

connection, and both of these connec

the ground wire at the 100 ft. line 

The noise background there is insign

compared to the recordings of Figure

and lob. 

(a) Vottage between line (black) to 

ground (green) VSP connected 

ho+,mon h7"nL ,.h;er, uro 

at service box. 

fb) Vottage between neutraZ (white) to 

ground (green) VSP connected 

between black and white. HLP at 

service box 

(el Noise background check 

Figure I0 

VoZtages betueen Conductors and Ground 

at End of 100 ft. (30rn) Line 

VI, CONCLUSIONS 

The tests on simulated high energy 

surges indicate that a transfer occurs from 

the VSP to the HLP at some current level 

depending on the distance between the two 

devices. 

Even for a short length of wire, the 

VSP is relieved from the surge by sparkover 

of the HLP before excessive energy can be 

deposited in the varistor of the VSP. At 

lower current levels where the voltage in 

the system is clamped by the VSP and thus 

prevents sparkover of the HLP, the VSP absorbs all of the surge energy. 

In all instances, the voltage le

the VSP is held low enough to protect 

electronic appliances having a reason

tolerance level (600 V in most cases

1000 V in extreme cases). Furthermo

installation of only one VSP in the h

already provides substantial protecti

other outlets, although optimum prote

requires the use of a VSP at the most 

sensitive appliance, with additional 

if further protection is required fo

sensitive appliances. 
VI I. REFERENCES 

F.D. Martzloff and G.J. Hahn, "Surge 

Voltage in Residential and Industrial 

Power Circuits," IEEE PAS-89, July/ 

August 1970, pp. 1049-1056. 

F.A. Fisher and F.D. Martzloff, "Transient Control Levels - A Proposal for 

Insulation Coordination in Low-Voltage 

Systems," IEEE PAS-95, January/February 

1976, pp. 120-129. 

J.H. Bull, "Impedance of the Supply 

Mains at Radio Frequencies," Proceedings 

of the 1st Symposium on EMC, Montreux, 

1975. IEEE 75-CH1012, 4 MOIYT. 

E.K. Howell and F.D. Martzloff, "High 

Voltage Impulse Testers," TIS 

75CRD075, Corporate Research and Development, General Electric Company, 

Schenectady , NY, March 1975. 
APPENDIX I 

Home Lightning Protector Specifications 

HOME LIGHTNING PROTECTOR 

Home Lightning Protector Page 

Listed by Underwriters' Laboratories (UL) sept. 2. 197

Effective Am. 8, 197

DESCRIPTION 

The Home Lightning Protector is designed to prevent lightning surges (entering through the wiring) from damaging 

electrical wiring and appliances. The Protector is a sturdy. 

weatherproof, service-proven device that immediately drains 

lightning surges harmlessly to ground. Installed at either the 

weatherhead or service-entrance box, the Protector discharges 

a surge in a fraction of a second. It will perform this protective 

function ova and over again. without any maintenance required, possessing the same long-life valve-type characteristics 

obtainable in higher-voltage distribution arresters. 

The Protector is a two-pole, thrce-wire device designed 

primarily for single-phase 120/240-volt three-wire grounded 

neutral service. It can also be applied to protect three-phase 

circuits where the line-to-ground 60 Hertz voltage does not 

exceed 175 volts. Connection diagrams are included on the 

inside of each carton. 

WHERE TO USE 

Farmers-whose livelihood depends on milking machines. 

incubators, coolers, submersible pumps, and other electrical 

equipment. 

Suburbanites-with considerable dependency on (and investment in) electrical appliances of all sorts. 

Rural Homeownersaften far from fire-fighting equipment. 

and repair facilities. 

Everyone--with electricd equipment exposed to the destructive lightning surges that can enter through directlyconnected overhead secondary power lines. 

The Gmaal Electric Home Lightning LISTED 

Protector 

-can prevent costly appliance repair . ... --can help provide uninterrupted electrical service 

-1-year unit replacement guarantee 

a LIGHTNING PROTECTIVE DEVICE 

PRICES AND DATA Dinribulion TransformrcP(O32) 

PERFORMANCE CHARACTERlSTICS * 

0-175 ( 2 / 1.0 1 1.2 1 1.1 

' Average valucs. 

Fig. 1. Worn- Llehlning Prot-ctor. H-rdwor. (not shown) Is Indude

In carton ond d.toi4.d below. 

Note - Service protector moy be mounted either side up - with bmchet. It may be 

Suspended by its 

leoda or maunted in 

kmckwts in bod center or fuse box-. 

'I I 2 l block leads NO. 14 AWG LOd* 

ore (I~nel 

tlnnad (1) white lead No 14 AWG 

COPPS (around) 1) Sec note Na 4 

(21 0 18" holes 

Included rlth protector 

I Alumanurn mountlnq brocket 

2 Alumanurn screw wrlh 

slotted heod 

3 Aluminum condull locknut " I 4 An olurnmum nod I mch 1- 

1% furnished to more securely 

mount the arrester 

Fig. 2. Model No. 9L15BCB002 Horn. Ll.hlnlng P.olrctor 

NOTE: Minimum order quantity is one (1) standard package 

containing twenty-four (24) units. Orders will be accepted fo

shipment from factory stock in- lots of one or more standard packages only. Orders for less than standard package quantities should be referred to local distributors. 

PUBLICATIONS: (Use latest issue) 

Descriptive Bulletin. . . . . . . . . . . GED-483

*Changed since May 13, 1974 Isrue. Price. ond doto svbiert to chonr.e without notica 

PM 7M). 701, 702, 711.714, 721.723, 731.737 
APPENDIX I1 

Voltage Spike Suppressor Product Information 

HI VI" rhp ~3x1 

VOLTAGE 

SPIKE 

PROTECTOR 

VOLTAGE SPIKES are brlef high voltage hich may occur in any electrical ZysTrn. ,hey may arise trom several sources, but in a home the two most mrnmon - - . .. . - . . are - - . 

switching OFF and ON appliances, 0 

a1r condltlmers. or furnaces within the house. 

surges on me power lines to the house caused by lighh

MAJOR CAUSE OF ELECTRONIC 

EQUIPMENT FAILURE 

Whde solla-state equapment IS much more reliable man tu

t pe equpment. ~t rr mom suscephble to voltage splke dama

Jrnal solkes shorten the life of som-state mrnmnents - . -. . .- w

. . 

large spikes- such as rho& which may-&& durlng lightn

storms -can destroy them instantty. 

SIMPLE, RELtABLE PROTECTION 

Plug the Protector inlo an t25V AC receptacle. Rug eq

men1 into the Protector. 1'0 protect more than one piece 

equipment, plug a multiple cutlet adaptor Into Protector. 

The Vdta Spike Protector mnths a GE-Movmvar~stor w

absorbs gogerm spkes but does not mtertere with nor

current tlow. It is des~gned to protect sensltlve elactro

equipment trom voltage spkes caused by the "sw~tch~

loads' or llghlnlng str~king the power lines Protector mll 

orotect aoalnst tW rare circumstances where Iiihtnnno str

ihe hou&, paver service takeoff. or antenna d&t~ - 

VOLTAGE SPIKE PROTECTOR HELPS PROTECT 

~OWE INDUSTRIAUCOMMERCIA

APPLIANCES EQUIPMENT 

N Sets Computers Radms Business Machines 

HvFi Equipment Industrial Conlrds 

Electronic Organs Test Equipment 

Major Appliances Mdil Equipment 

Some TV manufacturers are incorporat~ng GE-Mw' vari

&tfifhsi',~~,,~~&@,piuce reoau rates. These 

'.Ti:= 0Dtlon.l 

.. ... .. Wiring Device Department 

Q GE General Electric Co.. Prov.. R. 1.02940 @ 

-7LELECTRIC 

cat. NO. VSP-ID 
COORDINATION

OF

OVERVOLTAGE

PROTECTION

IN

LOW-VOLTAGE

RESIDENTIAL

SYSTEMS
Significance

Part 4 – Propagation and coupling of surges

Part 6 – Tutorials

This paper was presented as a summary tutorial aimed at the French-speaking Canadian community to solicit t

comments on the development of the IEEE Std 587 Guide. The paper has been translated into English by the

author to make the English-speaking community aware of that paper, which served at that time as one output fo

the release of the extensive test results that were reported in the 35-page GE Memo Report – still proprietary at 

time – “Lightning protection in residential AC wiring” (see Part 4 of the anthology). 

The tests were performed by injecting a simulated lightning flash current of unidirectional waveshape into the

grounding system of a simplified residential wiring system, and observing the coupling and induction of oscillato

surges in the house wiring

Part 8 – Coordination of Cascaded SPDs

Excerpts from the complete test report found in this summary include a discussion of the performance of gappe

arresters, as well as MOVs installed at the service entrance, with coordination with an MOV installed at the end 

branch circuits.

Filename: Coordination 1978
COORDINATION OF OVERVOLTAGE PROTECTION 

IN LOW-VOLTAGE RESIDENTIAL SYSTEMS 

F.D. Martzloff 

General Electric Company 

Schenectady, NY 

INTRODUCTION 

The development of metal-oxide varistors has made possible a 

substantial improvement in the mitigation of overvoltages in 

residential, commercial or light industrial power systems. For 

instance, transient suppressors are now available that can be 

plugged into a wall receptacle, thus making possible the 

protection of appliances or electronic devices that might be 

damaged by overvoltages occurring in power systems [I]. 

However, due to economic considerations, these suppressors 

have only a limited capability for absorbing high current 

surges that may be associated with lightning strikes occurring 

nearby. Thus, one may ask whether the installation of a 

suppressor with limited capability might not pose a risk of 

failure or create a false sense of security. 

It is then worthwhile to examine what occurs in a building 

provided with suppressors having different capability, located 

at different points of the building. as a function of the surge 

current intensity imposed by the lightning strike. Furthermore, 

the combination of several suppressors may allow a 

coordinated protection for reliable operation, which it would 

be worthwhile to demonstrate. 

CIRCUIT MODEL 

Given the complexity of distribution networks and the 

nonlinear response of the suppressors [2], it would be 

&f&.!t tc c,~Ip te 6- the L&b4;cr the 

S?l&~~t~l a ~~~ent SU~P T~IIC it is maere tn J----- e-- ---9 

the extent that res&y ~aq &, maJefi& hy a phy&d m&e!, in 

make tests directly on the devices actually used in these 

buildings. Such tests have been performed at the High Voltage 

Laboratory of the General Electric Company in Pittsfield, MA. 

We injected, into a physical model, currents corresponding to 

lightning strikes amplitudes ranging from moderate to 

extremely high 131. 

A model of a typical building was wired with the components 

used in a residential building: triplen overhead service drop 

from the distribution transformer, downconductor to the 

revenue meter, connection to the service panel provided with 

circuit breakers, with four branch circuits ranging from 5 to 50 

meters and provided with a receptacle at the far end. 

Assuming a 100-kA strike on the primary distribution system, 

an extreme case in the probability of discharges [3], a current 

division is postulated as shown in Figure 1, resulting from the 

injection of 30 kA in the (grounded) neutral conductor 

supplying the building. 

This 30-kA value is predicated by assuming that the lightning 

current transfers from the primary conductors to the grounding 

network as a result of the operation of the arrester, or by a 

K.E. Crouch 

Lightning Technologies, Inc. 

Pittsfield, MA 

//I - 1 "' 10D'<' 

I li xi OtlT TRANlrORYtO 

U YEIER 

"rFigure 1. Distribution of the 100-kA curre

in the ground network near the building 

flashover from the phase conductor to the ground co

the primary circuit, without involving the two con

the low-voltage distribution. Only the (grounde

conductor of the service drop is involved, with 70 k

through the grounding connection of the pole inv

toward the two adjacent poles. 

Figure 2 shows schematically the path of the 30-k

injected in the ground conductor to the building, as w

mechanism for inducing currents and voltages in t

model, mostly by electromagnetic coupling into 

formed by the service drop. 

PHASE WIRES 'MLSSENGLR' 

/ 

DISTRIBUTION 

TRANSFORMER 

RECEPIA":E 

CENTER 

VOLTAGE 

MEASURED 

RETURN Br 

- GROUND PLANE 

The complete circuit, including the surge generato

instrumentation, is shown schematically in Figur

course, the usual precautions were taken in the setup 

room for the instrumentation, checks for interferenc

@ 1978 IEEE. Translated from the original French version which first appeared in Proceedings, 1978 IEEE Canadian Confer

on Communications and Power, 78CH1373-0, pp 451-454. Permission to copy without fee is granted by the Institu

Electrical and Electronics Engineers if not made for direct commercial advantage. To copy otherwise, or to republish, req

a fee and specific permission. 
LIGHTNING 1 MODELDlSTRlBUTION 

CURRENT I TRANSFORMER mwmoR I AND smvm SHOP r I 

1 I 

\ i \wwxmwm 

I OR JUMPER WIRE 

GROUND 

CURRENT f \ /PLANE PROBE I _1__LMODEL HOUSE I SHIELDED I INSTRUMENT ! ROOM 

P . rlpre 3. Schemaiic of the exprimenti circuit 

Figure 4 shows an example of the waveform of the injected 

current, a 10125 ps impulse, which is a conservative hypothesis for the current involved. Three different values of the 

peak current have been used in the tests, 1.5 kA, 10 kA, and 

30 kA. The first value, 1.5 kA, is the standard duty test for 

a secondary arrester, the second, 10 kA, is the standard 

withstand test, and the last, 30 kA, is a pessimistic level. 

Figure 4. Injected current 

TYPES OF SUPPRESSORS 

There are two types of commercially available suppressors: a 

surge arrester that can be installed on the service panel or at 

the point of anchoring the service drop, and a suppressor 

which is a plug-in device as previously mentioned. 

The surge arrester type, which has been used for many years 

but only in limited numbers, meets the performance standard 

for a secondary arrester [4], in particular a rating of 10 kA, 

8/20 ps surge. One of the reasons for the lack of market 

success of this suppressor is undoubtedly the fact that its 

installation must be contracted out to an electrician because it 

requires work on the live circuits inside the service panel. 

Furthermore, this type of arrester has a let-through of about 

2000 V, which is excessive for sensitive electronic appliances. 

Varistor discs with a 32 mm diameter are now available, but 

only as an industrial component (at this time). These discs 

have the capability of diverting the 10 kA required by the 

standard, md thus are excellent candidates for a serviceentrance arrester because they can clamp at voltages 

si6cantly lower than those of previously available arresters. 

In the tests that we performed, these discs turned out to be 

highly promising. 

The plug-in type, represented in our test series by G

VSP-1, contains a 14-mm diameter varistor, with a 

6000 A and capable of absorbing a number of 3 k

during its service life. 

COORDINATION OF SUPPRESSORS 

In an installation where several surge suppre

connected at different points of the system, the suppre

the lowest clamping voltage will be called upon to 

the suppressor having a higher clamping voltage, by 

over first or by preventing the second from sparking 

reverse this situation, it is necessary that the voltag

the wiring, produced by the current flowing in 

suppressor and added to the clamping voltage of t

exceed the operating voltage of the second. In th

vg&~w, wh;rh hsp &-en dp~i~p& s@g!!y nrn

r---

clamping voltage, this situation may become critica

5 illustrates the arrangement where the VSP-1 migh

the HLP from sparking over if the clamping volta

VSP-1 is much lower than the sparkover voltage of 

This situation is another motivation for the tests, to v

coordination can be maintained between the suppr

practical applications. 

Sparkover of HLP: V1 5 VZ + Ri + Ldi

All the current in VSP-1: V1 > VZ + Ri = Ldi

Figure 5. Coordination between two 

suppressors separated by an impedance 

During a first test series conducted at 30 kA, we quic

that sparkover occurs at many points in the circuit, 

difficult to obtain reproducible results. It was nec

reduce the current to 1.5 kA to reach a situation 

sparkover would occur. Even at "only" 10 kA, spark

occurred in the unprotected devices (receptacle, servi

It should be noted that these sparkovers taking place 

the conductors (black to white or black to green) res

from injecting current in the ground conductor of th

not from injecting the surge directly into the phase co

Many oscillograms were recorded, which ca

reproduced in this paper. Some examples are giv

following figures, to enable comparisons among th

... 

arrannementr ..-. Of !he sgpp,,nTpSgO,,nTr, ShowLqa that an 

b""'""" b ------ 

protextion scheme can be achieved, if only a few pr

are taken. 

Effect of the inductance at the end of the line 

Oscillograms 204, 247, and 248 (Figure 6) 

attenuation obtained from an impedance at the end o

for a 1.5 kA injection, at the end of a 25-m line. Os

204 shows an opencircuit voltage reaching 2200 

oscillations at about 500 kHz decaying in about 20 
Open-circuit 

Voltage 

500 Vidiv 

2 psldiv 

Voltage with 

130-$2 load 

500 Vidiv 

2 psldiv 

Voltage and current 

in the VSP-1 with 

130 $2 and VSP-I 

Figure 6. Effect of impedance at the end of the line 

By connecting a resistive load of 130 $2 at that point, the 

voltage is reduced down to 1400 V, and the oscillations are 

replaced by a damped waveform. Adding a varistor (VSP-1) 

to the 130-R resistor produces the clamping shown in oscillogram 248; this oscillogram also shows that only 15 A flow in 

the varistor. From these oscillograms, the followiog conclusions ' may be drawn: an oscillatory voltage at 500 kHz is 

induced the line, superimposed td the unidirectional voltage 

produced by the injection of an unidirectional current. This 

oscifiaiory voiiage appears to be the resuit of osciiiations . iii . the he, "sci~a~ions i'nai can be hp& by 

addii~g a i&Ave !od at the eii of ihe he. Furthermore, 

connecting a 13043 resistor at the end of the line reduces the 

voltage at the end of the line from 2200 to 1400 V. One may 

view this situation as a voltage divider consisting of the source 

impedance and the impedance at the end of the line. A rough 

estimation of the "source" impedance, Zs, may be made by 

neglecting the complex nature of the impedances. The circuit 

equation may be written as Vr = Vo 130/(130 + Zs), where 

Vr is the voltage (1400 V) recorded with a resistor in the 

circuit, ad Vo is the open-circuit voltage (2200 V). Solving 

for Zs yields Zs = 75 Q. This value, although inaccurate 

because the equation was not vectorial, is nevertheless a useful 

result to provide an order of magnitude for the source impedance, the perennial question. 

?&XEXUXc3 ~f Siiiiiii&3SOiS 2: :he ~ei-<ice siiiimce 

Osciiiograms 143, 261, 263, and 153 (Fig~re 7) show the 

resuiis obtained by instaiiing various types of suppressors at 

the service panel, for a 10 kA surge. Without any protection 

(oscillogram 143), the voltage reaches 7 kV before collapsing 

to small oscillations. This collapse is actually the result of a 

breakdown occurring at some other point of the circuit, as 

demonstrated in other tests. This oscillogram shows that 7 kV 

peaks may be reached when no protection is provided. 

Voltage without 

protection 

2 kVldiv 

2 psidiv 

Varistor on 

the outside 

500 Ndiv 

500 Vldiv 

2 pidiv 

Varistor on 

the inside 

500 Ndiv 

500 Vidiv 

2 pstdiv 

HLP Arrester 

400 Aldiv 

500 Vldiv 

2 pldiv 

Fiyre 7. Compared performance of vari

suppressors at the service panel 

By installing a 32-mm disk outside the service 

arrangement that requires a total of about 50 cm of 

protective level shown in Oscillogram 263 is obta

800 V, with high-frequency oscillations reachin

while about 1100 A flow in the disc. If the disc i

directly onto the bus bars of the panel, with a 

connection length of about 15 cm, the protecti

substantially improved: oscillogram 261 shows osc

only 900 V and subsequent value of 600 V, with a 

about 1200 A in the disc. In contrast, the HL

(oscillogram 153), which contains a spark gap 

carbide varistors, allows the voltage to reach 240

sparking over, then holds a discharge voltage of a

with a peak current of i'3W A. This set of me

shows how important it is to hoid the connections 

-- - -1L 1. rm~ ~ -- pusslula. imey also show how ihe new metai-oxid

c;;;; ;?;pic;e pioiEtioii, if c"iieci;y inshiid. 

Stress on the suppressors 

Considering the limited capability of the VSP-1 de

is only a 14-mm disc and does not purport to be 

arrester, it is interesting to determine the stress th

imposed by injecting a surge with extreme value. 
-- 77 .mm dice ---- incirlp. 

Voltage and current 

for VSP-1 at 12 m 

500 Ndiv 

500 Vldiv 

2 psldiv 

32-mm disc outside 

Voltage and current 

for VSP-1 at 12 m 

200 Aldiv 

500 Vldiv 

2 pldiv 

No protection on the panel 

Voltage and current 

for VSP-1 at 12 m 

1000 Aldiv 

500 V/div 

2 pldiv 

No protection on the panel 

Voltage and current 

for VSP-I at 25 m 

lo00 Ndiv 

500 Vldiv 

2 psldiv 

Figure 8. Stresses on the suppressors 

Figure 8 shows the resuits of tests made with an appropriate 

protection at the service panel (oscillogram 275), with a poor 

protection at the service panel (281), and without any protection at the service panel (283 and 284). 

With a disc connected directly across the bus bars (275), the 

ideal situation, the current in a VSP-1 located 12 m away from 

the service panel, resulting from injecting 30 kA, is less than 

400 A; the voltage across its terminals, to be applied to the 

protected load, is less than 500 V. If now the disc is installed 

outside of the panel (281), a reduction of the effectiveness of 

the protection, the current in the VSP-1 is slightly increased, 

with a corresponding increase in the clamping voltage. If no 

protection is installed at the service panel (283), the VSP-1 

would tend to absorb all the current, in this case a 3.3-kA 

peak with a clamping voltage of 650 V for a VSP-1 installed 

12 m away. In contrast, for a VSP-1 installed 25 m away, the 

voltage drop between the panel and the VSP-1, associated with 

the line impedance, is such that a breakdown occurs upstream 

from the receptacle (in this case in a parallel branch circuit), 

hence the limiting effect shown in oscillogram 284. 

Thus, this set of measurements shows that even in the extreme 

case of injected currents, the current imposed to the VSP-1 

remains within acceptable limits for a limited number of 

Certified translation by French Associates, Inc, Gaithersburg MD 20877. 

4 

s~rgs. Its ,gag =f (933 A & fj!20 p dews w"

nf Am A fet the prd~rt he, ~;thigh 

Furthemore; this example illustrates the fact that 

can occur in a poorly coordinated installation. From 

of view of the safety of the VSP-1, the breakdown 

oscillogram 284 might be viewed as a safety valve

the overall safety point of view, it is not recommen

upon a breakdown occurring in the wiring or at the 

of the wiring devices, because such breakdown ma

power fault with significant fire hazard. 

CONCLUSIONS 

1. It is sufficient to inject, in the ground condu

service drop, a surge current corresponding to a 

lightning stroke to reach hazardous voltages between 

and neutral conductors within the building. 

2. Commercially available protective devices are 

limiting overvoltages to acceptable limits; even in 

an injection corresponding to extreme vaiues, sever

ments may be considered: 

a) A lightning arrester consisting of a spa

silicon carbide varistors can limit the overvoltage

2000 V, eliminating the risk of breakdown in the 

the attendant fire hazard. This 2000 V limit provid

tion for conventional appliances but may be ina

protect electronic devices that tend to be more sen

b) A metal-oxide varistor, presently availa

an industrial component package, correctly instal

service panel (short connections) would be sufficie

overvoltages for all the building, even for high 

lightning strokes. 

b) A varistor with limited capability, t

installed at a particular receptacle, will limit over

ihai point to values that are ac~ephtbit: fur ei~irv

-- w;ruour .-AL -- -. gag kse~r exp d k-dsa ib

from a - zet pt&iC= -- IS g

ch~t 10 mes. &r dift-~e~, t& stress 

the VSP-1 might exceed the expected reliability, w

of the varistor. This failure would still provide 

during the surge, but lead to a trip of the panel br

course, if a protection according to (b) were pr

would not be necessaty to install a VSP-I. If the 

provided at the service panel is less than ideal (

addition of a VSP-1 at the receptacles that suppl

devices would provide protection for these devices

HLP would provide diversion of high currents. 

REFERENCES 

[I] Surge Voltages in Residential and Mustr

Circuits, F.D. Martzloff and G.J. Hahn, IEEE Tr

PAS Vol 89, pp 1049-1056, JulylAugust 1970. 

[2] Qt'estee .... !ex vaistacp. ? ?~pr by V.

".,-.,--. 70umnl Nn . .-. 410, pp 50-55, 28 Se@emk.r 1977. 

[3] A Ground Lighming Environment for Engineeri

N. Cianos & E.T. Pierce, Stanford Research Instit

Park CA, August 1972. 

[4] Surge Arresters for Alternating-Current Powe

ANSI C62.1-1975. 
COORDINATION

OF

SURGE

PROTECTORS

IN

LOW-VOLTAGE

AC

POWER

CIRCUITS
François D. Martzloff 

General Electric Company 

Schenectady NY 

f.martzloff@ieee.org

Reprinted, with permission, from IEEE Transactions on Power Apparatus and Systems, PAS-99, Jan 1980 

First presented at IEEE Summer Meeting, Vancouver, July 1979

Significance: 

Part 4 – Propagation and coupling of surges 

Part 8 – Coordination of cascaded SPDs 

This paper presents a summary of two earlier and detailed proprietary General Electric reports describing 

experiments conducted in Schenectady NY and in Pittsfield MA, respectively by Martzloff and Crouch. (These 

have now been declassified by General Electric and are included in this Anthology – see Coordination 1976

and Propagation 1978.) The prime purpose of that paper at the time was to report in a non-classified 

platform experimental results that could be useful for the development of IEEE Std 587 (later known as IEEE 

Std C62.41).

In the first experiment, a simple test circuit of two branch circuits originating at a typical service entrance paper 

was subjected to relatively high-energy unidirectional impulses, with various combinations of surge-protective 

devices installed at the service panel and/or at the end of the branch circuits. That 1976 experiment was the 

beginning of recognition of the “cascade coordination” issue that became the subject of intense interest in the 

80’s and 90’s (see the listing of contribution by many authors in Part 1, Section 8). 

In the second experiment, the coupling and subsequent propagation of surges was investigated in a more 

complex circuit that included a distribution transformer, service drop, entrance panel, and several branch 

circuits. The surge was injected in the grounding system, not into the phase conductors. This 

experiment thus brought new evidence that ring waves can be stimulated by unidirectional surges. 

Nevertheless, the threat was considered at that time as a surge impinging onto the service entrance from the 

utility, not resulting from a direct flash to the building grounding system. On that latter subject, see Dispersion

and Role of SPDs. 

This paper received the 1982 Paper Award from the Surge-Protective Devices Committee. 

Filename: Coordination 1980
F.D. Martzioff, Member, IEEE 

General Electric Company 

Schenectady, NY 12345 

- Surge protectors can be installed in low-voltage ac power systems 

to limit overvoltages imposed on sensitive loads. Available devices offer a 

range of voltage-clamping levels and energy-handling capability, with the 

usual economic trade-off limitations. Coordination is poss~ble between lowclamping-voltage devices having limited energy capability and high-clampingvoltage devices having high energy capability. The paper gives two examples 

ofcoordination, as well asadditionalexperimental resuitson surge propagation. 

1. INTRODUCTION 

Surge voltages occurring in low-voltage ac power circuits have two origins: 

external surges, produced by power system switching operation or by lightning, 

and internal surges, produced by switching of loads within the local system. 

Typical voltage levels of these surges are sufficient to cause the failure of sensitive electronic appliances or devices, and high surges can cause the failure 

of rugged electromechanical devices (clocks, motors, and heaters) [I ,2]. 

For many years secondary surge arresters from a number of manufacturers 

have been available. These arresters are effective in protecting nonelectronic 

devices against the high-voltage surges associated with lightning or power system switching. However, the voltage allowed by an arrester is still too high for 

sensitive electronic devices. Furthermore, installation requires an electrician 

to connect thedevice on hot terminals. 

The advent of the metal oxide varistor packaged as a convenient plugin 

device or incorporated into the appliances makes possible a voltage clamping 

which is more effective than that of the conventional secondary arrester. However, ihe energyhandling capability of such packages is lower than that of an 

arrester, so that large currents associated with lightning strikes cannot be 

handled by these packages. 

The availability of these two different types of suppressors now makes it 

possible to obtain a coordinated protection of all the appliances in a home or 

all the equipment in an industrial environment. Improper coordination, however, could force the lower voltage device to assume all the current, leaving the 

high-energy protector uninvolved; this situation could then cause premature 

failure of the low-voltage suppressor. This paper discusses the elements of a 

coordinated protectivesystem based on experimentation. 

11. SECONDARY ARRESTERS AND LOW-VOLTAGE 

SUPPRESSORS 

Typical secondary arresters for 120 V service consist of an air gap in series 

with a varistor made of silicon carbide. The device is generally packaged with 

two arresters in the same housing; the physical arrangement is designed for installation on the outside of a distribution panel, through a knockout hole of 

the panel enclosure or at the entrance to the building. 

Limitations on the gap design imposed for the purpose of reliable operation and clearing after a high current discharge(10 kA, 8 x 20)do not allow the 

sparkover of the gap to be less than about 2OOO V. This sparkover and the 

time required to achieve it allow injection of a potentially damaging surge into 

the "protected" power system downstream from the arrester: While this 

2000 V level provides better protection than the protective characteristics indicated in ANSI standards [3], lower voltage clamping is desirable for the 

protection of sensitive electronics. 

*In this paper the high-energy suppressor, typically installed at the service 

entrance, will be called arrester. The low-enersv. low-voltaae suooressor. - .. typically installed at an ourlet or incorporated intoan applianceor connected 

load, will be called suppressor. 

F 79 635-4 A paper recamended and approved by the 

IEEE Surye Protective Devices Cornnittee of the IEEE 

Power Engineering Society for presentation at the IEEE 

PES S-r Meeting, Vancouver, British Coldia, 

Metal oxide varistors suitable for I20 V line applications can clamp surge 

voltages at less than I000 V, typically at 500 to 600 V for surge currents of less 

than 1000 A. These varistors provide excellent protection for electronic systems. The economics of device size, however, limits the wlde use of large varistors, especially since smaller varistors can do an acceptable job if they are not 

exposed to excessive currents. Proper coordination among the devices used 

is required to obtain a reliable protect~on system. 

111. PROTECTION COORDINATION 

While the installation of surge protective devices functions effectively for 

high-voltage utility systems coordinated by centralized engineering, thecurrent 

trend toward regulatory installation in low-voltage systems, because they are 

seldom centrally engineered and coordinated, can result in damaged equipment and system failure. The successful application of protective devices to a 

low-voltage system demands a perspective of the total system, as well as a 

knowledge of individual device characteristics. Where such knowledge and 

coordination are lacking, a low-voltage suppressor installed in conjunction 

with an arrester can prevent the voltage at the terminals of an arrerter from 

reaching its sparkover level. As a result, all of the surge current may be forced 

into the suppressor, wh~ch may not have been intended to withstand extreme 

conditions. 

Proper coordination in an arrester/suppressor system requires some impedance between the two devices. This impedance is generally provided by the 

wiring: at the beginning of the surge, the rapidly changing current produces 

an inductive voltage drop in this wiring, in addition to the drop caused by the 

resistanceof the wiring. Thus, thevoltageat theterminalsof thearrester during 

the current rise of the surge is equal to the clamping voltage of the suppressor, 

plus the voltage drop in the line (tests reported below indicate that this voltage 

drop is indeed appreciable). This voltage addition can then raise the terminal 

voltage of the arrester sufficiently to reach sparkover. In this way the arrester 

will divert most of the surge current at the entrance, rather than permitting it 

to flow in the suppressor. 

The application of a suppressor alone is likely to occur because electronic 

appliance manufacturers increasingly provide suppressors incorporated into 

their products. With no arrester at the service entrance, the wiring clearances 

can become a voltage-limiting device, thus establishing a clearance/suppressor 

system. The suppressor would again tend to assume all of the surge current 

flow. The voltage drop in the line, in a manner similar to that of the arrester/ 

suppressor system, would raise the voltage at upstream points to levels that 

may spark over the clearances of wiring devices, providing unplanned rehef 

for the suppressor. When sparkover of the clearances occurs. there are three 

possible results: 

a. A power-follow current occurs, with destructive effects on the 

components. 

b. A power-follow current occurs, but overcurrent protection (breaker 

or fuse) limits the damage. The system can be restored to operation 

after a mere nuisance interruption. 

c. No power-follow current takes place; the overvoltage protective 

function of the system can be considered as accomplished. 

The concept of protecting solid insulation by allowing clearances to spark 

over first is actively promoted by the Low Voltage Insulation Coordination 

Subcommittee of the International Electrotechnical Commission [4]. 

Further discussion of it is outside the scope of the present paper; nevertheless, 

the concept is worth attention because cost reductions and system reliability 

could be obtained through its proper application. 

Two examples of protection coordination will now be discussed in detail. 

These examples represent two scenarios on surge injection; they are based on 

experiments involving an arrester and suppressors in simulated lightning surge 

conditions. In the first scenario the surge is assumed to be ~njected between 

one of the phase wires and the center conductor (ground) of the service entrance. In a second scenario thesurgecurrent is assumed to be injected directly 

into the ground system of a service entrance only. Both experiments show the 

benefits and importance of proper coordination. In both tests the arrester was 

a gap-silicon carbide combination (Fig. I) and the suppressor, a metal oxide 

varistor in a plugin package (Fig. 2). 

IV. SURGE APPLIED BETWEEN PHASE AND GROUND 

Test Circuits 

The test circuit (Fig. 3) consisted of a terminal board from which two lines, 

one 7.5 m (25 ft )long and the other 30 m (100 ft) long were strung in the test 

area. A short, 3 m (10 ft), line simulated the service drop. All of these lines 

Canada, July 15-20, 1979.~~~~~~~i~t submitted February 6, were made of three-conductor, nonmetallic. #I2 AWC sheath wire. The neu1979; made available for printing April 3, 1979. tral and ground wires of the three lines were connected together at the terminal 

board and from there to the reference ground of the test circuit. 

0018-9510/80/0100-0129$000075@ I980 IEEE 
(a) (b) 

Fig. 4. Open-circuit voltage and short-circuit current (without any protector). 

Fig. 1. Typical arrester for service entrance installation. 

Fig. 2. Typical suppressor for plugin installation. 

GR~EN 

IGROUNDl 

Fig. 3. Test circuit. 

All surge currents were applied between the line conductor (black) at the 

end of the service drop and the reference ground (green and white). These 

impulses were obtained from a 5 pF capacitor charged at a suitable voltage 

and discharged into the wiring system by an ignitron switch. The resultant 

open-circuit voltage waveform, a unidirectional wave of 1 ps rise time x 50 ps 

to one/half value time, corresponds to the standard test wave in utility systems. 

Fig. 4 shows typical open-circuit voltage and short-circuit current waveforms. 

Voltages were recorded by a storage oscilloscope through an attenuator probe 

(1000:l); currents, through a current probe and a current transformer. Thus, 

the calibrations displayed on the oscillogram are to be multiplied by 1000 for 

the voltage. The current traces show the 50 mV setting corresponding to the 

rated output of the current probe, with the amperes per division shown in 

parentheses corresponding to the current transformer ratio and current probe 

input setting for a direct reading. The sweep rate is also shown on the oscillograms, at IOps/div. for all the tests. 

Test Results 

Fig. 5a shows the voltage across the arrester when subjected to the surge defined by Figs. 4a and 4b. Note that the sparkover voltage reaches 2200 V, with 

several oscillations, before the voltage settles down to the impulse discharge 

voltage at about 2000 V at its start. 

Figs. 5b and 5c show, respectively, the voltage and current across the varistor in the suppressor. Note that the maximum voltage is 600 V for a 550 A 

current on the varistor. (The current in the suppressor is lower than the available short-circuit current as a result of the reduced driving voltage, because 

the varistor holds off 600 V. 

Fig. 6 shows several osc~llograms indicating how the surge propagates in 

the wiring in the absence of any wppressor. Fig. 6a shows the open-circuit 

voltage at the service box. At the open-ended 7.5 m (25 ft) line, the voltage is 

substantially the same as at the box (Fig. 6b). However, at the end of the 30 m 

(100 ft) line with a 50 Q termination, a significant decrease of the slope is noticeable, while the crest remains practically unchanged (Fig. 6c). 

(a) open-circuir volrage-ai box 

(b) open-clrcult vollage-7.5m (25 ill (cl open-clrcuil voltage - 30m (IW fl) 

Fig. 6. Propagation of surge 

With voltage limitmg at the box provided by the installation of a suppressor, even at a remote outlet, an arrester connected at the service box would not 

reach its sparkover voltage until rubstantial surge currents were involved. A 

larger current was requ~red for a short distance between the service box and 

the suppressor than for a greater distance. The value of the current required 

to reach sparkover as a function of the distance is therefore of interest. 

For a distance of 7.5 m (25 ft) the threshold condition for sparkover of the 

arrester is shown in Fig. 7. In Figs. 7a and 7b the open-circuit voltage and 

short-circuit current are shown for this threshold setting of the generator. Inspection of the oscillograms shows an open-circuit voltage of 8.1 kV, with a 

calculated equivalent source impedance of 4.2 R. This low value of the source 
impedance, compared to proposed values 151, provides a conservative evaluation of the system performance. For the same setting as Figs. 7a and 7b, the 

oscillograms of Figs. 7c and 7d show the case in which the arrester has sparked 

over, as indicated by its voltage (7c) and current (7d) traces. In Figs. 7e and 7f, 

the traces show the voltage (7e) and current (70 in the suppressor for a case in 

which the arrester did not spark over (as a result of the scatter of sparkover or 

a slight difference in the output of the surge generator). This case represents 

the most severe duty to which the suppressor would be exposed, for a distance 

of 7.5 m (25 ft). 

(a) opncircult vokagc (b) short-circuit current 

(c) voltageat arrester when arrester dm sparkover - suppressor at 7.5 rn (25 11) 

(d) current in arrester after sparkover - 

suppressor at 7.5 m (25 It) 

(e) voltageal suppressor when arrestor does no1 

sparkover - suppressor at 7.5 rn (25 11) 

(0 current in suppressor when arrester docs not sparkover - suppressorat 7.5 m (25 R) 

Fig. 7. Transfer of surge conduction 

From these tests it is apparent that the I200 A flowing in the line to the 

suppressor (70 and establishing 1000 V at the varistor terminals (7e) causes an 

additional 1OOO V drop in the line. The resulting 2000 V appearing at the arrester terminals may cause sparkover of the arrester (7c). 

For a case in which there is no arrester installed at the box but only the 

suppressor installed at an outlet, the voltage rise in the wiring and the meter 

coils will most likely result in a flashover of the system, which would then divert the excessive energy away from the suppressor, just as the arrester did in 

the test. Of course, this diversion may be destructive, a result that the arrester, 

when ~nstalled, is prec~sely designed to prevent. 

For greater distances between the suppressor and the arrester, the transfer 

of the surge wtll occur at lower currents. For instance, w~th the suppressor 

installed at the end of the 30 m (100 ft) line, only 700 A were required in the 

suppressor to reach sparkover of the arrester. 

Discussion 

The tests on simulated high-energy surges indicate that a transfer occurs 

from the suppressor to the arrester at a current level which depends on the distance between the two devices. Even for a short length of wire, the suppressor 

is relieved from the surge by sparkover of the arrester before excessive energy 

can be deposited in the varistor of the suppressor. At lower current levels, 

where the voltage in the system is clamped by the suppressor and thus prevents 

sparkover of the arrester, the suppressor absorbs all of the surge energy. 

In all instances, the voltage level at the suppressor is held low enough to 

protect all electronic appliances having a reasonable tolerance level (MX) V in 

most cases, IOOO V in some cases). Furthermore, the installation of only one 

suppressor in the house provides substantial protection for other outlets, 

although optimum protection requires the use of a suppressor at the most sensitive appliance, with additional suppressors for other sensitive appliances. 

V. SURGE INJECTED INTO GROUND SYSTEM 

Assumptions 

For this experimenl it was postulated that a lightning stroke attaching to 

the primary side of an overhead distribution system would produce a branching of the current flow into the ground after sparkover of the pole-mounted 

utility's surge arrester (which was presumed connected at the pole-mounted 

distribution transformer). Fig. 8 shows the assumed circuit and the division 

of current flow. 

LEGENO 

LA PRIMARY ARREST 

IF OlST TRANSFORMER 

t 

Fig. 8. Division of current assumed for a 100 kA stroke. 

In their study of lightning environments, Cianos and Pierce [61 indicat

that only 5% of all ground strokes exceed a peak current of 100 kA. The fre

quency of the strokes is dependent upon the geographic location (isokerauni

levels) (71, as well as upon local configurations. The probable mcurrenc

of a stroke involving the utility pole near a house with no adjacent tall trees o

buildings is I per 400 years for most of the U.S. For a 5% probability

the likelihood can be reduced 20 times; in areas of high lightning activity, thi

likelihood can be reduced 10 times. A stroke exceeding 100 kA at one loca

tion, therefore, can be expected to occur only once in 10,000 years (but ther

are millions of poles in the U.S.). 

From these assessments, the maximum current to be injected for the hous

model under discussion was selected to be 30 kA. From this maximum o

30 kA injected into the ground wire of the houseservice drop, two more value

were used during the test series: 10 kA, corresponding to the requirement fo

the ANSl high-current, shortduration test; and 1.5 kA, corresponding to th

requirement for the ANSl duty-cycle rest -both specified by ANSl Standar

C 62.1 for secondary valve arresters (31. All had wavethapes of 8 x 20 ps. 

Another reason for selecting this low level (1.5 kA) was that no sparkove

occurs in the wiring at this level. For the 10 and 30 kA levels, multiple flash

overs occur at variable times and locations, making exact duplication of test

impossible. By limiting current to below sparkover levels, repeatability of th

results was ensured, allowing comparisons among several alternate circui

configurations. 

The generation of transient voltages in the house is attributed to electro

magnetic coupling. The lightning current in the messenger establishes a fiel

that couples into the loop formed by the two phase wires encircling the mes

senger. In addition, there is some capacitive coupling between the wire

(Fig. 9). 

Fig. 9. voltages induced in the house wiring system. 

Test Circuit 

The test circuit consisted of a high-current impulse generator, a distribu

tion transformer with a service drop, a simulated simplified house wiring sys

tem, and the necessary shielded instrumentation. 

The service drop connection between the distribution transformer and th

meter socket was made with three 13 in: (45 ft-) long AWC #6 wires, twisted 

at a pitch of about 5 turns/m (1.5 turns/ft). This service drop was folded in 

loose '5" shape at about 0.5 m (1.5 ft) above the ground plane serving as th

return path for the lightning current, in order to reduce the loop inductanc

seen by the generator. This configuration does not influence the coupling be

tween the messenger and the wires wrapped around it, coupling which has bee

identified as the voltage-inducing mechanism. 
The simulated house wiring started at the meter socket and continued to a 

load center over a distance of 3 rn (10 ft). From this load center four "branch 

circuits" connected to the load center breakers were established, each terminating at a wall receptacle. Individual lengths of the branch circuits were 6, 

12.24. and 48 m (20.40. 80, and 160 ft). 

Test Results 

Many tests were performed to investigate the effects of various combinations. A selection was made from ceveral hundred recorded oscillograms to illustrate these effects. The results are presented in the form of oscillograms 

with corresponding commentary, generally providing a comparison of voltages 

and currents with or without protectors installed. 

The first striking result noted was that the injection of a unidirectional impulse into the ground system produces oscillatory voltages between the phase 

and ground wires. Inspection of the no-load oscillogram (Fig. IOa) reveals 

two interesting phenomena. First, the frequency of the major voltage oscillation is constant for all branch circuit lengths (period = 2 ps). Thus, we can 

conclude that this frequency is not affected by the line length and that other 

circuit parameters, rather, are responsible for inducing this 500 kHz oscillation 

from a 8 x 20 ps current wave. Second, the minor oscillations visible during 

the first loop in each oscillogram are spaced apart at a distance that increases 

with line length. One can conjecture that these may be caused by reflections. 

Loading the line termination with a 130 Q resistor (Fig. lob) eliminates the 

later oscillations and reduces the first peak to about 60% of the value without 

load. From this reduction. a Thevenin's calculation of circuit oarameters. if 

applicable in an oversimplified form, would show that 130 51 is 60% of the 

total loop impedance, while the source impedance* is 40% of the total loop 

impedance. Hence. one can conclude that the equivalent source impedance 1s 

in the order of four-sixthsof 130, or about 85 R, in this scenario. 

VOLTAGE WITH 1300 

COhNFCTFn ATOUTI FT 

INDICATED 

Sweep lpr dn 

h, VO tascat outkt mdrated SW V dn 

Fig. 10. Open-circuit voltages and effect of terminal ~mpedance. 

Injected current: 1.5 kA. 

With no protectors at the load center nor at any outletc, the wiring flashes 

over at I0 kA injected current, but not before crests in the range of 8 kV have 

been reached (Fig. 1 la). With an arrester installed at the load center, voltages 

are limited to 2.2 kV, with about I kA current discharge in the arrester 

(Fig. Ilb). While eliminating the hazard of a wiring flashover or the failure 

of a typical electromechanical device, this 2.2 kV protective level may still be 

excessive for sensitive electronics. 

VOLTAGE AND CURRENT WITH 

ARRESTER ON LOAD 

CENTER 

Sweep: 2 rddiv 

Current In arrescer 400 A/dw 

Voltage Across Bur 

5W V/d~v 

Fig. 12 shows the recordings made during a 30 kA current injection. This 

extreme condition is capable of producing a 3500 A current in an arrester installed at the service entrance (Fig. 12a). If now we postulate a pessimistic 

situation where there is no arrester at the service entrance, but only a suppressor at an outlet, there are two possible outcomes. When no wiring sparkover 

occurs, as discussed in Section Ill, all the surge is indeed forced upon the suppressor (Fig. 12b). This current may be excessive for some suppressors, but 

this example is certainly a limited case. The more likely scenario is illustrated 

in Fig. 12c, where sparkover of the wiring upstream of the suppressor limits 

the current in the suppressor. In this last scenario, protection is obtained 

downstream from the suppressor. It is important to note that no additional 

hazard is created by installing the suppressor: the undesirable sparkover 

would occur even without the suppressor; in fact, without the suppressor, 

sparkover would be even more likely to occur. 

Current In 

suppressor: I kAldlv 

Voltage at 

outlet: 5W V/dw 

Sweep: 2 @r/diu 

Current in 

suppressor: I kA/dlv 

Voltage a1 

outlet: SWV/div 

Sweep: Zps/div 

(c) Wiring Flashover 

Fig. 12. Duty imposed on stngle suppressor with 30 kA injection 

VI. CONCLUSIONS 

Coordination of surge protectors is feasible with existing devices, even if 

device characteristics vary. The experiments reported in the paper show three 

facts from which conclusions can be drawn: 

Fact I. Where a unidirectional current is injected into the ground system 

only, the responseof the system is an oscillatingvoltage, at 500 kHz 

for the system described. 

Fact 2. The equivalent source impedance, as determined by loading the 

system, is in the range of 50 to 100 R for the particular system 

investigated. 

Fact 3. Without substantial connected loads in the system, the open-circuit 

surges appearing at the service entrance propagate along the branch 

circuits with very little attenuation. 

Concl. 4. Coordination of surge suppressors requires a finite impedance to 

seoarate the two devices. enabline the lower voltaee device to oerConcl. 5. 

Concl. 6. 

fokm its voltaee-clamoine func~i~n while the hieher voltage debice . - performs the energydiverting function. 

The concept that surge voltages decrease from the service entrance 

to the outlets is misleadmg for a lightly loaded system. Rather, the 

protection scheme must be based on the propagation of unattenuated voltages. 

Indiscriminate application of surge protector? may, at best, fail to 

provide the intended protection and, at worst, cause disrupt~ve 

operation of the suppressors. What is needed ir a coordinated approach based on the recognition of the e%ential factors governing 

devices and surge propagation. 

Fig. 11. Protection provided by arrester at service entrance. VII. ACKNOWLEDGMENT 

Injected current: I0 kA. 

The contribution of K. E. Crouch in obtaining the current injeclion lest 

'Not to be confused with the surge impedance (L/C)'/' of the line. results i5 gratefully acknowledged. 
REFERENCES 

1. Martzloff. F.D., and G.J. Hahn. "Surge Voltage in Residential and 

IndustrialPowerCircuits," IEEE PAS-89,6, luly/Aug. 1970, 1049-1056. 

Lenz, J.E., "Basic Impulse Insulation Levels of Mercury Lamp Ballast 

for Outdoor Applications," Illuminating Engrg., February 1964, 

pp. 133-140. 

Guidefor Applicalion of Valve-Type Lighrning Arresters ForAlternaling 

Current Systems. ANSI Standard C62.2-1969. 

Insularion Coordination Within Low- Volrage Systems Including Clearances and Creepage Distances for Equipmenl, International Electrotechnical Commission Report SC28A (Central Office) 5, to be published 

in 1979. 

Guideline on Surge Voltages in AC Power Circuits Rated Up ta 600 V. 

IEEE Project P587.1, First draft, 1978. 

Cianos. N. and E.T. P~erce "A Ground-Lightning Environment for 

Engineering Usage," Sranford Research Institute, Menlo Park, CA 

94205, August 1912. 

Elecrrical Transmission and Distriburion Reference Book, Westinghouse 

Electric Corporation, 4th Edition, East Pittsburgh, Pa., 1950. 

Francois D. Martzloff (M, 1956) was born in 

France and received his undergraduate degree at 

the Ecole Sp6ciale DeM6caniqueet d'Electricit6 

in 1951; he received the MSEE degree from 

Georgia Tech in 1952 and the MSIA degree 

from Union College in 1971. 

Since 1956 he has been with the General 

Electric Company, where he first gained experience in the Transformer and Switchgear 

Divisions. Upon joining General Electric 

Corporate Research and Development in 1961, 

, he became involved in power semiconductor 

c~rcuits and overvoltage protection. He has 

oartici~ated in the introduction and aoalication . . bf metal oxide varistors since 1971. 

In IEEE Mr. Martzloff has been active on the Surge Protective Devices 

Committeeand chairman of the Working Groupon Surge Voltagesin AC Power 

Circuits Rated 6W V or Less. He is also a member of the Ad Hoc Advisory 

Subcommittee of the USA Advisory Committee on IEC S/C 28A. He has 

been awarded 10 U.S. patents, primarily in the field of varistors and transient 

protection. 
COORDINATION

OF

TRANSIENT

PROTECTION

FOR

SOLID-STATE

POWER

CONVERSION

EQUIPMENT
Significance

Part 6 – Tutorials

Part 8 – Coordination of Cascaded SPDs

This paper was presented as a tutorial aimed at a semiconductor-oriented audience, giving an overview of the o

of transient overvoltages and of IEEE and IEC documents under consideration in the early eighties, identifying a

categorizing transients. A brief review of available techniques and devices follows, with a description of the

principles of coordinated protection, specific experimental examples, and results reconciling the unknown with th

realities of equipment design.

The themes emphasized that effective protection of sensitive electronic equipment is possible through a system

approach where the capability of the equipment is compared to the characteristics of the environment, a basic te

of the electromagnetic compatibility documents. As more field experience is gained in applying these documents 

equipment design, the feedback loop can be closed to ultimately increase the reliability of new equipment at

acceptable costs, while present problems may also be alleviated based on these new findings in the area of

transient overvoltages.

Filename: Coordination 1982
THE COORDINATION OF TRANSIENT PROTECTION 

FOR SOLID-STATE POWER CONVERSION EQUIPMENT 

F.D. Martzloff 

p ------ +- L --A n * ----- Lulpulai= RGJG~ILII auuuevewpn~eni 

General Electric Company 

Schenectady, New York, USA 

ARSTRACT 

Tramier?! avervn!!ages are n= !snge: a: unknown thiea: 

to the successful application of power conversion equipment, 

thanks to the availability of protective techniques and .d--.:--- vL:- uev~r;s. LIII~ paper presents an overview of the origin of 

transient overvoltages and of recent IEEE and IEC documents identifying and categorizing transients. A brief review 

of available techniques and devices follows, with a description of. the principles of coordinated protection, specific 

experimental examples, and results reconciling the unknown 

with the realities of equipment design. 

INTRODUCTION 

Sixe the ktrndwtier! cf semics::duc:ors, :imsieiit oveivoltages have been blamed for device failures and system 

malfunctions. Semiconductors are, indeed, sensitive to overvoltages. However, data have been collected for several 

years on the occurrence of overvoltages, to the point where 

the problem is now mostly a matter of economics and no 

longer one of lack of knowledge on what the environment of 

,. ,, ,. ,", .-y' -----*--' r~.+~a a,aLCLl.a ILL io ~UUIIY ~IULOLLGU semiconducior 

circuits. This statement may represent a slight oversimplification of the general problem because the environment is stiii defined in statistical terms, with unavoidable 

uncertainty as to what a specific power system can impress on 

a specific piece of power conversion equipment. 

The IEEE has published a Guide (1) describing the 

nature of transient overvoltages (surges) in low-voltage ac 

power circuits. This Guide provldes lniormation on the rate 

of occurrcnre, on the caveshape, am? a: :he eneigj.. 

associated with the surges, as a function of the location 

within the power system. In addition, the IEC has issued a 

report concerning insuiaiion coordination i2j, identifying 

four categories of installations, with a matrix of power system voltages and overvoltages specified for controlled situations. Other groups have also proposed test specifications, 

some of which are now enshrined in standards that may be 

applied where they are really not applicable, but have been 

applied because no other information was available at the 

time. 

At this time, the environment seems to be defined with 

su@rient de!zi!. Ecxvever, there is sti!! a !ack of giiibance on 

how to proceed for specific instances, and circuit designers 

may feel that they are left without adequate information to 

make informed decisions on the selection of component 

characteristics in the field of overvoltage withstand or protection. This situation has been recognized, and various groups 

concerned with the problem are attempting to close 

by preparing application guides which will provid

specific guidance than a mere desciipiioii of the 

ment, although that description in itself is already a c

able step forward. 

One of the difficulties in designing a protection sc

the industrial world of power conversion equipmen

absence of an overall system coordinator, in contras

world of electric utilities, for instance, which are g

under the single responsibility of a centralized eng

sigaiiization. The user or" power conversion equip

likely to purchase the materia! from a supp!ier indepe

of other users of the same power system, and coor

of overvoltage protection is generally not feasibl

thoan rnn,4;+;n..n y{-rn- ..... 'I- -.- -l 

., Vua. . ULJG JGL, aii uu~uurumateu appii

surge suppressors can lead to wasteful or ineffective 

allocation, since independent users would each att

provide protection in adjacent systems or inde

designers would provide protective devices in adjac

systems. 

To shed more light on this situation. this paper w

review some of the origins of transient overvoltag

reference to recently published IEEE and IEC doc

which provide guidance on !he envire~mer.:. Te

and protective devices will then be discussed, and e

of coordinated approaches presented. 

THE ORIGIN OF TRANSIENT OVERVOLT

Two major causes of transier?! nvervn!!sger h

been recognized: system switching transients, and t

triggered or excited by lightning discharges (in co

direct lightning discharges to the power systems, w

generally quite destructive, and against which total p

may not be economical in the average application)

switching transients can involve a substantial par

power system, as in the case of power factor c

capacitor switching operations, disturbances following 

tion of power after an outage, and load shedding. H

these do not generally involve large overvoltages (m

two or three per unit), but may be very difficult to 

since the energies are considerable. Local load s

especially if it involves restrikes in switchgear dev

piobiice higher voitages ihan ihe power system s

but generally at lower energy levels. Considering, 

the higher impedances of the local systems, the threa

sitive electronics is quite real, and only a few con

case histories of failures can cast an adverse shado

large number of successful applications. 
VOLTAGE LEVELS 

Two different approaches have been proposed to define 

voltage levels in ac power systems. At this time, the divergences have not yet been reconciled, as each proposal has its 

merits and justification. The IEEE approach involves reciting 

a rate of occurrence as a function of voltage levels, as well as 

of exposure in systems that do not necessarily use protective 

devices. The IEC approach indicates only a maximum level 

for each location category, but no higher values are expected 

because this approach implies the application of protective 

devices. These two proposals will be quoted in the following 

paragraphs. 

The IEEE Guide (IEEE Std 587-1980) 

Data collected from a number of sources led to plotting a 

set of lines representing a rate of occurrence as a function of 

voirage for three iypes of exposures iii iiiiprotected ciifiits 

(Figxe !!. These exposure levels are defined in general 

terms as follows: 

0 Lnw Exposure - Systems in geographical areas known 

for low lightning activity, with little load switching 

activity. 

0 Medium Exposure - Systems in geographical areas 

known for high lightning activity, with frequent and 

severe switching transients. 

High Exposure - Rare but real systems supplied by long 

overhead lines and subject to reflections at line ends, 

where the characteristics of the installation correspond 

to high sparkover levels of the clearances. 

It is essential to recognize that a surge voltage observed 

in a power system can be either the driving voltage or the 

voltage limited by the sparkover of some clearance in the 

SURGE CREST. kV 

*In some locations, sparkover of clearances may limit 

the overvoltages 

Figure 1. Rate of surge occurrence versus voltage level in 

unprotected circuits from IEEE Std 587 

system. Hence, the term unprotected circuit must 

stood to be a circuit in which no low-voltage 

device has been installed, but in which clearance 

will eventually limit the maximum voltage. The d

of surge levels, therefore, is influenced by t

producing mechanisms as well as by the sparkove

clearances in the system. 

The voltage and current amplitudes presente

Guide attempt to provide for the vast majority o

strikes but should not be considered as "worst ca

this concept cannot be determined realistically. O

think in terms of the statistical distribution of strik

ing a reasonable upper limit for most cases. W

consequences of a failure are not catastrophic b

represent an annoying economic loss, it is appr

make a tradeoff of the cost of protection against 

lihood of a failure caused by a high but rare surge. 

The IEC Approach (IEC Report 664, 1980) 

In a report dealing with clearance requirements 

A:- - ----A:--*:-- -..-----" LIUII CUUIU~IL~LIUII YUI~UJG~, thc !EC Subcmmitte

recommends a set of impulse voltages to be con

representative of the maximum occurrences at 

points of a power system, and at levels dependent 

system voltage (Table I). The report is not prim

cerned with a description of the environment, but 

insulation coordination of devices installed in thes

This approach rests entirely on the establishmen

trolled levels in a descending staircase, as the wirin

progress within the building away from the service 

The fundamental assumption made in establ

levels of Table I is that a decreasing staircase of ov

will evolve from the outside to the deep inside of 

(system), either as the result of attenuation caus

impedance network, or by the installation of overv

:+--o IIC-IJ LIL ot +ha ~ur ;ntnrLr,=r LLLL~LAUUVLI. 

if the descending siaircase of voiiages is prov

surge pratective device a! each interface, it must 

nized that the successive devices will interact; the 

not one of one-way propagation of the surges. 

protective device installed, say, at the 111111 inter

be so close (electrically) to the device at interface 

it could prevent the latter from operating; in ot

the 111111 device might face the surge duty normall

to be handled by the IVIIII device. Thus, a vita

the selection of interface devices is that of ensur

coordination. 

Table I 

PREFERRED SERIES OF VALUES OF IM

WITHSTAND VOLTAGES FOR RATED VO

BASED ON A CONTROLLED VOLTAGE SI

Voltages line-to-earth 

derived frx? ra!d 

system voltages, up to: 

(V rms and dc) 

Preferred series of impulse w

vn!t.ges in ins!a!!a!ion ca!ee

I I 

I 1 11 1 111 

50 

1000 
In both the IEEE standard and the IEC report, the 

assumption has been made that the surge is impinging the 

power system through the service entrance and is occurring 

between phase and earth. Experience has shown that a frequent cause of distress is the voltage differences existing 

between conductors reputed to be at ground potential; in 

fact, one of them is elevated above the other by the flow of 

surge current. This situation, not addressed in either document, needs to be recognized and dealt with on an individual, case-by-case basis, lest a false sense of security be 

created by restricting the protection to the power service 

entrance. 

WAVESHAPE OF THE 

TRANSIENT OVERVOLTAGES 

Observations in different locations (3-6) have established +I.... ruaL the iiiObt fieqiieiii type of iiiiiiskiii overvoiiage iii aC 

power systems is a decaying oscillationj wi!h frequencies 

between 5 and 500 kHz. This finding is in contrast to earlier 

attempts to apply the unidirectional double exponential 

voiiage wave, generaiiy described as i.2i50, aitnough .the 

unidirectional voltage wave has a long history of successful 

application in the field of dielectric withstand tests and is representative of the surges propagating in transmission systems 

exposed to lightning. The IEEE Guide recommends two 

waveshapes, one for the indoor environment, and one for 

the outdoor and near-outdoor environment (Figure 2). Not 

only is a voltage impulse defined, but the discharge current, 

or short-circuit current of a test generator used to simulate 

these transients, is also defined in the IEEE document. 

The oscillatory waveshape simulates those transients 

affecting devices that are sensitive to dvldt and to voltage 

reversals during conduction (7). The unidirectional voltage 

and current waveshapes, based on long-established ANSI 

standards for secondary valve arresters, simulate the transieiiis where eiieigji conieni is ihe significant parameier. 

ENERGY AND SOURCE IMPEDANCE 

The energy involved in the interaction of a power system 

with a surge source and a surge suppressor will divide 

between the source and the suppressor in accordance with 

the characteristics of the two impedances. In a gap-type 

suppressor, the low impedance of the arc after sparkover 

OpenCircuit Voltage, 

Curreni Deiined by Tabie ii 

forces most of the energy to be dissipated elsewhere

the power system series impedance or in a resistor 

series with the gap for limiting the power-follow cur

an energy-absorber suppressor, by its very nature, a 

tial share of the surge energy is dissipated in the su

but its clamping action does not involve the pow

energy resulting from the short-circuit action of a g

therefore, essential to the effective use of sup

devices that a realistic assumption be made about th

impedance of the surge whose effects are to be dupli

Unfortunately, not enough data have been coll

what this assumption should be for the source impe

the transient. Standards or recommendations eith

the issue, such as MIL STD-1399 or the IEC Repo

its present published form,' ot they sometimes 

values applicable to limited cases, such as the SWC 

eieciioiiic eqilipmerii operating in high-voirage 

!ions (81. The !FEE Guide z!!emp!s to re!z!e im

with three categories of locations, A, B, and C. F

industrial environments, Categories A or B wi

Category C is intended for outdoor sttuations (Table 

MATCHING THE ENVIRONMENT 

WITH THE EQUIPMENT 

On the basis of the various documents mention

preceding paragraphs, an equipment designer or 

take a systematic approach to matching the transie

voltage capability of the equipment with the enviro

which this equipment is to be installed. This des

involve tests to determine the withstand levels (

measurements andlor analysts to determine the d

hostility of the environment, and a review of avail

tective devices. The latter will be discussed in the 

paragraphs. 

Transient Suppressors 

Two methods and types of devices are ava

suppress transients: blocking the transient throu

;ow-pass fl;iei, oi diveriiiig it to gro"iid ibroiig'il so

linear device. This nonlinearity may he either a f

nonlinearity (high-pass filter) or a voltage no

Continuing studies by the IEC SCl28A Working Group 

addressing this issue, and additional publications are anticipa

Open Circuit Voltage Discharge Current 

Indoor Environment Outdoor and Near-Outdoor Environment 

Figure 2. Transient overvoltages and discharge currentsin IEEE Std. 587-1980 
(clamping action or crowbar action). In this paper, a majority 

of the discussion will center on the latter type, since voltage 

clamping devices or crowbar devices are the most frequently 

used (10). 

Voltage-clamping devices have a variable impedance, 

depending on the current flowing through the device or the 

voltage across its terminals. These components show a nonlinear characteristic, i.e., Ohm's law E=RI, can be applied 

but the equation has a variable R. Impedance variation is 

monotonic and does not contain discontinuities, in contrast 

to the crowbar device which shows a turn-on action. As far 

as volt-ampere characteristics of these components are concerned, they are time-dependent to a certain degree. However, unlike sparkover of a gap or triggering of a thyristor, 

time delay is not involved here. 

When a voltage-clamping device is installedj the circuit 

remains unaffected by the device before and after the transient for any steady-state voltage below clamping level. 

increased current drawn through the device as the voitage ottomnto tn rieo rocralta in lrnltooo rlomninn artinn Tnrroorprl U.."L..YLL L" ..Y" LVYULLI 1.1 ."..Ub" ".Ul..yl.lb YILIVLI. .I'"I"U.,"U 

voltage drop (IZ) in the source impedance due to higher 

current results in the apparent clamping of the voltage. It 

should be emphasized that the device depends on the source 

impedance, Z, to produce the clamping. X voltage divider 

action is at work where one sees the ratio of the divider not 

constant, but changing (Figure 3). The ratio is low, however, if the source impedance is very low. The suppressor 

cannot work at all with a limit zero source impedance. In 

contrast, a crowbar-type device effectively short-circuits the 

transient to ground. Once established, however, this short 

circuit will continue until the current (the surge current as 

well as any power-follow current supplied by the power system) is brought to a low level. 

Figure 3. Voltage clamping action of a suppressor 

The crowbar device will often reduce the line voltage 

below its steady-state value, but a voltage clamping device 

will not. Substantial currents can be carried by the crowbar 

suppressor without dissipating a considerable amount of 

energy within the suppressor, since the voltage (arc or 

forward-drop) during the discharge is held very low. This 

characteristic constitutes the major advantage of these 

suppressors. However, limitations in volt-time response, 

power-follow, and noise generation are the price paid for this -A 

au vauiagc. AS -.-I.^-- vulrage IIIU cases au uss a spark-gap, 

significant conduction cannot take place until transition to the 

arc mode has taken place by avalanche breakdown of the gas 

between the electrodes. The load is left unprotected during 

the iniiiai rise due to this deiay time itypicaiiy in 

microseconds). Considerable variation exists in the sparkover voltage achieved in successive operations, since the process is statistical in nature. For some devices, this sparkover 

voltage can also be substantially higher after a long period of 

rest than after successive discharges. From the p

nature of the process, it is difficult to produce con

sparkover voltage for low voltage ratings. This diffi

increased by the effect of manufacturing tolerances o

small gap distances. This difficulty can be alleviated by 

the tube with a gas having lower breakdown voltage th

However, if the enclosure seal is lost and the gas is r

by air, this substitution creates a reliability problem b

the sparkover of the gap is then substantially higher. 

Another limitation occurs when a power current fr

steady-state voltage source follows the surge di

(follow-current or power-follow). In ac circuits, this 

follow current may or may not be cleared at a natural 

zero. In dc power circuits, clearing is even more unc

Additional means must, therefore, be provided to op

power circuit if the crowbar device is not designed to p

seif-ciearing action within specified iimits of surge 

'..rrtnm .rnltona ",.A nn..mr~f~llP...r 0.. -ma..* ojorul~~ vvrrtlgr, -UV pvwrn -IVIIVW ~ULL~I~L. 

A third iimitation is associated with the sharpness 

spxkover, which produces fgs! current rises in !he 

and, thus, objectionable noise. A classic example 

kind of disturbance is found in oscillograms recordi

sparkover of a gap where the trace exhibits an anomaly 

the sparkover (Figure 4). This anomaly is due to th

introduced in the oscilloscope circuits to provide an ad

trigger of the sweep. What the trace shows is the 

delayed by a few nanoseconds, so that in real time, 

sparkover occurs while the trace is still writing th

sparkover rise. Another, more objectionable effect 

fast current change can be found in some hybrid pro

systems. Figure 5 shows the circuit of such a dev

(a) Open clrcult lOkV 1 rs (b) SWrkover of 120 V Ar

at 1600 V In 550 ns 

Figure 4. Interference to oscilloscope circuits caus

gap sparkover 

Figure 5. Hybrid protector with gap 
found In the commerce. The gap does a very nice job of 

discharging the impinging high-energy surges, but the magnetic field associated with the high di/dt induces a voltage in 

the loop adjacent to the secondary suppressor, adding what 

can be a substantial spike to the expected secondary clamping 

voltage. Consequently, most electronic circuits are better 

protected with voltage clamping suppressors than with 

crowbars, but sometimes the energy deposited in a voltage 

clamping device by a high current surge can be excessive; a 

combination of the two devices can provide effective protection at optimum cost. However, this combined protection 

must be properly coordinated to obtain the full advantage of 

the scheme. The following paragraphs will discuss some of 

the basic principles of coordination and provide some 

examples of applications. 

PROTECTION COORDINATION 

One of the first concepts to be adopted when considering 

a coordinated scheme is that current, not voltage, is the 

independent vanable involved. The physics of overvoltage 

geneia:ian invop;e &hei ;ightiiing or laad swiiciiiiig. Both 

are current sources, and it is only the voltage drop associated 

with the surge current flow in the system impedance which 

appears as a transient overvoltage. Perhaps a long history of 

testing insulation with voltage impulses has reinforced the 

erroneous concept that voltage is the given parameter. Thus, 

overvoltage protection is really the art of offering low 

impedance to the ./?ow of surge currents rather than attempting 

to block this flow through a high series impedance. In combined approaches, a series impedance is sometimes added in 

the circuit, but only after a low impedance diverting path has 

first been established. 

When the diverting path is a crowbar-type device, little 

energy is dissipated in the crowbar, as noted earlier. In a 

voltage clamping device, more energy is deposited in the 

device, so !hat !he energy hxx!!ing c~p~bi!i!y ef E sandld~te 

suppressor is an important parameter to consider when 

designing a protection scheme. With nonlinear devices, an 

error made in the assumed value of the current surge pro- A,.,.n" 1;ttl" arrrrr "UGbO lllllb bIIV1 'h" .,^I+^"" '"^""A ""'^"" +I.^ rllr vurragb de.*b!urbu auuaa uib 

suppressor and thus applied to the protected circuit (1 

the error is directly reflected in the amount of energy 

the suppressor has to absorb. At worst, when surge cu

in excess of the suppressor capability are imposed 

environment, because of an error made in the assump

because nature tends to support Murphy's law or beca

human error in the use of the device, the circuit in n

protection can generally be protected at the price of fai

the short-circuit mode of the protective device. Howe

substantial power-frequency currents can be supplied 

power system, the fail-short protective device general

minates as fail-open when the power system fault 

failed device is not cleared by a series overcurrent pro

device (fuse or breaker). Note that in this discussio

term "fail-safe" has carefully been avoided since it can 

opposite failure modes to different users. To some, f

means that the protected hardware must never be expo

an overvoltage, so that failure of the protective devic

be in the faii-short mode, even ~f ~t puts the system 

eperatlox. TG ether users, %i!-safe meaiis that the f

must be maintained. even if the hardware is left temp

unprotected, so that failure of the protective device m

in the open-circuit mode. 

EXAMPLES OF COORDINATED 

SURGE PROTECTION 

Retrofit of a Control Circuit Protection 

In this case history, a field failure problem was cau

lack of awareness (on the part of the circuit designer) 

degree of hostility in the environment where the circ

to be installed. A varistor had been provided to prot

control circuit components on the printed circuit boar

its capability was exceeded by the surge currents occur

a Category B location (Table 11). To the defense of t

cuit designer, however, it must be stated that the d

Table I1 were not available to him at the time. 

Since a numher of devices were i, service, co

redesign was not possible, and a retrofit - at an acc

cost - had to be developed. Fortunately, the powe

sumption of this controi circuit was iirilited so that 

Table I1 

RECOMMENDED VALUES FROM IEEE STD 587 

Surge Voltages and Currents Deemed to Represent the Indoor Environment 

and Recommended for Use in Designing Protective Systems 

Energy (joules) 

Type Deposited in a Suppressor* 

Comparable to Impulse of Specimen with Clamping Voltage of 

Location IEC No 664 Medium Exposure or Load 500V lO0OV 

Category Category Waveform Amplitude Circuit (120 V System) (240 V Syste

A Long branch 

Circuits and 

outlets 

6 kV High impedancet - I1 0.5 ps-100 kHz 200 A Low impedance+, 8 0.8 

B Maicr feeders. .-. V Ln .." L.4 A 0" pa 63 iiiipedancet - - 

short branch III 8 X 20 ps 3 kA Low impedance? 40 80 

circuits, and 6 kV High impedancer - - load center 0.5 /.&-100 kHz 500 A Low impedance*, 8 2 7 A 

- -- ~ -- -~ ~ p~ ~ -p - - - - - - - - 

*ether sq,,presers ha..*xg afferent vo:tages wo.&d receive &;fereiii levels. 

 or high-impedance test specimens or load circuits, the voltage shown represents the surge voltage. In making simulation tests. 

that value for the open-circuit voltage of the test generator. 

 or low-impedance test specimens or load circuits, the current shown represents the discharge current of the surge (not the sho

circuit current of the power system). In making simulation tests, use that current for the short-circuit current of the test generator

8~he maximum amplitude (200 or 500 A) is specified, but the exact waveform will be influenced by the load characteristics. 
possible to insert some series impedance in the line, ahead of 

the low-capacity varistor, while a higher capacity varistor was 

added at the line entrance to the circuit (Figure 6). Laboratory proof-test of the retrofit demonstrated the capability of 

the combined scheme to withstand 6 kA crest current surges 

(Figure 7A) and a 200% margin from the proposed 

Category B requirement, as well as reproduction of the field 

failure pattern (Figure 7B). The latter is an important aspect 

of any field problem retrofit. By simulating in the laboratory 

the assumed surges occurring in the field (Table II), 

verification of the failure mechanism is the first step toward 

an effective cure. Figure 7C illustrates the effect of imprope 

installation of the suppressor, with eight inches of leads 

instead of a direct connection across the input terminals of 

the circuit. 

TERMINAL RETRO-FIT MULTI-PIN 1 - BOARO PROTECTIVE CONNECTOR DEVICE P.C. BOARD PACKAGE 

Figure 6. Retrofit protection of control circuit 

Coordination Between a Secondary Surge Arrester and a 

Varistor 

In this example, the objective was to provide overvoltage 

protection with a maximum of 1000 V applied to the protected circuit, but to withstand current surges on the service 

entrance of magnitudes associated with lightning, as defined 

in ANSI C62.1 and C62.2 standards for secondary arresters. 

The only arresters available at the time which could withstand a iO kA crest 320 ps impuise naci a protective kiamping! !eve! cf ~pproximate!y 220G V (!2!. Some dls!axce was 

available between the service entrance and the location of the 

protected circuit, so that impedance was in fact inserted in 

series between the arrester and the protected circuit where a 

varistor with lower clamping voltage would be installed. The 

object was to determine the current level at which the 

arrester would spark over for a given length of wire between 

the two protective devices, relieving the varistor from the 

excessive energy that it would absorb if the arrester would 

not spark over. 

A circuit was set up in the laboratory (13), with 8 m 

(24 ft) of #12 (2.05 mm) two-wire cable between the 

arrester and the varistor. The current, approximately 

8/20 ps impulse, was raised until the arrester would sparkover about half of the time in successive tests at the same 

level, thus establishing the transfer of conduction from the 

varistor to the arrester. Figure 8A shows the discharge 

current level required from the generator at which this 

transfer occurs. Figure 8B shows the voitage at the varistor 

when the arrester dees m! spa:!: we:. Figure 8C sh~w :he

voltage at the arrester when it sparks over: this voltage 

would propagate inside all of the building if there were no 

suppressor added. However, if a varistor is added at eight 

meters, the voltage of Figure 8C is attenuated to that shown 

Upper trace: Voltage across 

V15OLAl varistor on PC board, 

200 Vldiv. 

Lower trace: Applied surge current, 

2000 P.!div. 

Sweep speed: 10 &div. 

Additional surge protection removed: 

Vl5OL.Al varistor on PC board is 

the only protection. 

Upper trace: Voltage across -.. --- V I >ULA I varistor 

Lawr trace: Vxis!gr curre"! 

200 Aldiv. Sparkover occurs at 

about 700 A: 60 Hz power-follow 

de~tioy~ the PC board. 

Sweep speed: 10 &div. 

Same as A, but with varistor 

mounted on e~ght-~nch leads lrom 

termin.! herd. 

Figure 7. Laboratory demonstration of re

effectiveness 

in Figure 8D, at the terminals of the varistor. 
Figure 8. Transfer of conduction in a coordinated 

Y".-'..w crhprnp nf ". nrnt~rtinn y.Y.YI..Y.. 

rnK-.-L.-- ~vliatcni~r~ Suppressor Cnpririiiiy to the Environmeni 

It is a recognized fact that varistors exhibit, as do many 

other components, an aging characteristic, so that a finite life 

can be predicted. Most manufacturers provide information 

on this aspect of application, and IEEE standards identify this 

parameter as one of the significant evaluation tests (14). 

Carroll has shown (15) how statistical information presented 

in IEEE Std 587 can be combined with Pulse Lifetime Ratings published by manufacturers (16) to arrive at a rational 

selection of device ratings, with a specific life goal, in a costeffective manner. 

However, these ratings are generally expressed as a 

number of pulses of constant value, e.g., the rated life of a 

given varistor may be 1 pulse of 6 kA at 8/20, 10 pulses at 

2 kA, 1000 pulses at 500 A, and so forth. But since the 

si;iges ei;coiiii;eieb iii life have a range of a 

slope of probability versus magnitude described hy Figure I, 

one must consider the effect of this array of pulses with 

, 

UUG~W~ VL~LUG~ IL~UIF.~ ~11.11 the coiisiaiii piiises imp

the manufacturer's pulse lifetime rating. 

The method described by Carroll in the reference

provides a computation that can be applied in genera

but repeating it here would be too lengthy. Rather, 

take two examples of application and develop a table 

how the Pulse Lifetime Ratings can be combined w

data from IEEE Std 587 to make a reasonable estim

the rated life consumption. The computations shown 

tables have been made with four digits for the sake o

ing a check of the arithmetic, but the base data are f

four significant digits in their accuracy, and the numb

read from curves with rather coarse logarithmic scales

ever, these examples do illustrate the method and the 

that can be expected. 

The first task is to convert the voltage surge dens

abiiiiji of Figiire i inio a hisiogram of surge curre

farr?i!y of surge vo!!age ce!!s car? be defified frsm the F

line, with the density read at the center of the ce

number of occurrences for any cell is then the value 

ordinate of the line, minus the number of total occu

of all cells to the right of the cell of interest. In the 

tations of Table 111, this conversion is shown in t

three columns, indicating the voltage level at the cell 

the number per year, and the number of occurren

year. 

From the description of the Category B in IEEE S

one can deduce an implied source impedance of 6 k

for a surge or 8/20 ps, or 2 a as the most s

Category B. The current that will flow in a varist

nected at this Category B location is then the surge 

minus the varistor clamping voltage, divided by t

source impedance of the surge. The varistor clampi

age can be determined if the current is known, so a

tion would be required to obtain the clamping voltage

ever, one can assume a ciamping voiiage, and iaier ch

va!ic!i!y of !he assumption agains! !he reru!!ifig 

obtained. The fourth column of Table111 sho

Table 111 

LIFE CONSUMPTION - 14 mm, 130 V RMS VARISTOR, 

CATEGORY B, LOW EXPOSURE 

Assumed Voltage Number clamping Available Surge current Rated number Percent life 

surge per occurrences voltage of driving @ 2 pulses consumed 

level year per year at varistor voltage A for this 

v per year above level level v surge current 

-- 

Cumulative life consumption per year 

Time to reach rated life. years 
assumed and subsequently checked value of the clamping 

voltage, hence the value of the available driving voltage in 

the next column, and the resulting surge current value, 

assumed to be an 8/20 ps waveshape. 

Turning then to the published Pulse Lifetime Ratings, 

one can read the rated number of pulses corresponding to 

the surge current for each cell. Table 111 is computed with 

the ratings for a 14 mm varistor (Figure 9a); Table IV is 

computed for a 32 mm varistor (Figure 9b). Note that this 

"rated life" is defined as the condition reached when the 

varistor nominal voltage has changed by 10%; this is not the 

end of life for the varistor, but only an indication of some 

permanent change beginning to take place. The varistor has 

still retained its voltage clamping capability at this point. 

For each level of surge current, the number of pulses is 

read on ihe famiiy of curves of Figures 9a or 9b, aiong the 

vertica! ~xis, since these 2re 8/20 ps impc!ses. The number 

of pulses with constant amplitude is shown in the next-to-last 

column of Table 111. We can now define, for each level, the 

percentage of life consumed for one year of exposure at that 

level. For instance, at the 2500 V level of Table 111, there 

will be 0.01 surges of 1010 A per year, with 10 allowed by 

the ratings. Therefore, in percent, the life consumption is 

(O.Ol/yr x 100)/10, or 0.10%. Likewise, taking the 900 V 

level, the consumption is (O.l/yr x 100)/2000 = 0.04%. 

The total of these life consumptions at all cell levels is then 

0.43% of the rated life in one year, yielding an estimated 

232 years for this 14 mm varistor to reach its rated life in the 

Low-Exposure Category B environment. 

Similar computations for a 32 mm varistor in a 

Category B, Medium Exposure, are shown in Table IV. In 

the case of this "Medium Exposure," we note the high frequency of occurrences below 3000 V, reflecting the "frequent and severe switching transients" cited in the IEEE 

definition of Medium Exposure. Thus, a still very conserva- 

!ive es:ima:e :v~u!d be !ha: as many as ha![ of :he 

occurrences would be due to lightning. with the attendent 

8/20 ps high energy surges, while the other half would be 

switching transients, having a lower energy content than the 

8/20 ps surges accounted in this computation, being oscillatory as typified by the 0.5 us - 100 kHz wave. This 

20 50 100 200 500 IOM 2000 5000 IO.OW 

IMPULSE OURlTlON - pl 

50.000 7 --~- YODEL SIZE 32mm rp v[3&~15il 

.,, I 

VI5OMEISO 

y lO.000 1 + 1 -4 

~,ooo~*--+,~~t--+- 4 ~ ---- ~ I 

I. 

200 

: I00 

r 50 

k 20 

0 

u I0 

2 5 

220 50 100 1-I. 200 500 1000 2000 5000 10,000 

IMPULSE DURATION -*I 

NOTE: 

End of l8letmw IS defsned as d deqradatlon faalute which occurs when the 

devkce exh~txts a sh~ft In the varlstor voltage a1 one Ill m~ll~ampere In exce

of + 104, of the ln~tm value Thts type 01 fatlure Is normally a result of a 

decredslnq V1 vdlue. but does not prevent the device from conllnulng to fu

Howevet. the varistor will no longer meet the orig~nal spec~ficartons 

Figure 9. Pulse lifetime ratings 

translates to 13 surges of 760 A, 35 surges of 525 A, a

surges of 285 A, still a high number of lightning surg

therefore certainly conservative. Using this conse

estlmate of half of the low-magn~tude surges and all 

I.:"l. ^..--^" LA:-- 8/?(? ps I:-L.^:^- 

~tte~t-~~~a~ut~uub 3~1563 ~61115 II~$IIUIIII~-

surges. the computation of Table IV yields 21 years to 

rated life for the 32 mm varistor. In thls case, whe

rated life is reached earlier, ~t should be pointed out t

results are strongly influenced by the assumption ma

the source impedance. Using the IEEE 587 implied v

Table IV 

LIFE CONSUMPTION - 32 mm, 150 V RMS VARISTOR, 

CATEGORY B, MEDIUM EXPOSURE 

Voltage Number Total Occurrences Clamping Available Surge Rated number 

surge per occurrences due to voltage driving current of pulses for life 

level year per year at lightning of varistor voltage @ 2 0 this surge consumed 

V above level level V V A current 

Cumulative life consumption per year 

Time to reach rated life, years 
2 il ieads to these conservative resuits. For example, the 

FCC test for communication equipment interfacing with 

power lines (17) implies a 2.5 source impedance. Current 

studies for complementary data to the IEC Report 664 make 

the assumption of a surge originating on the primary of a distribution transformer, with a 63 source impedance, yielding currents of less than I kA available at the service 

entrance interface. Thus, there is still room for more precise 

definitions of the source impedance, but we should recognize 

that any attempt to make broad generalizations will always 

encounter the contradiction of some special cases. 

CONCLUSION 

Effective protection of sensitive electronic equipment is 

possible through a systematic approach where the capability 

of the equipment is compared to the characteristics of the 

environment. The combined efforts of severa! orga~izatiom 

have produced a set of data which provide the circuit 

designer with reasonable information, albeit not fine 

specificaiions, on the assumptions to be made in assessing 

the hos!i!ity of the mvirmrr?~~!. With the pubkcatio:: of the 

IEEE Guide, and of application guides in the near future, we 

can expect better knowledge of the power system environment. As more field experience is gained in applying these 

documents to equipment design, the feedback loop can be 

closed to ultimately increase the reliability of new equipment 

at acceptable costs, while present problems may also be 

alleviated based on these new findings in the area of transient overvoltages. 

ACKNOWLEDGMENTS 

The data base for the Guide quoted in the paper as well 

as the writing of that Guide was provided by the members of 

the IEEE Working Group on Surge Characterization in LowVoltage AC Power Circuits. Robert Mierendorf emphasized +ha o;nn;firn..na -f nlanrn..-l. ....--I-- .--. --A D..&-- n:,~ 9- 

ruu a&guuz+nurr ut +lralallro ~palh~.Vcl, allu rcLG1 RlLllllldIl b 

critique of the concepts relating to source impedance proved 

very effective; and, Eric Carroll's cross examination of the 

IEEE Std 587 led to the concept of relating varistor pulse I:''-*.-- .,-A LL- >.-L-'L..& 

IIIGL~IIIG uala io rut: uiw~ou~iun of expected surge currents. 

REFERENCES 

"IEEE Guide for Surge Voltages in Low-Voltage AC 

Power Circuits," IEEE Std 587-1980. 

"Insulation ~- - Coordination Within Low-Voltage -. Systems 

Including Clearances and Creepage Distances for Equipment," International Electrotechnical Commission 

Report 664 (1980). 

J.E. Lenz, "Basic Impulse Insulation Levelg of Mercury 

Lamp Ballast for Outdoor Applications," Illuminating 

Engrg., pp. 133-140 (February 1964). 

F.D. Martzloff and G.J. Hahn, "Surge Voltage in Residential and Industrial Power Circuits," IEEE PAS 89 

(6), pp. 1049-1056 (JulyIAugust 1970). 

R. Hasler and R. iagadec, "Digital Measurement of Fast 

T--..O;~ to -.. D-..7ar C,d..nl.r T :-an ') DWnn ? rl C.,-nno:.,- lallolrnro ",, . un,,, pp,J LL,L,,or , VL. J~U UylllliVI)IIIIII 

and Technical Exhibition on Electromagnetic C~m~uatibility. 

Rotterdam, Holland, pp. 445-448 (May 1979). 

6. F.D. Martzloff "Transient Overvoltages in S

Systems," General Electric Company 

81CRD121, Schenectady, NY (1981). 

7. P. Chowdhuri, "Transient-Voltage Characteristi

coti Power Rectifiers," IEEE IA-9 (5)

(SeptemberIOctober 1973). 

8. "Guide for Surge Withstand Capability," 

ANSIIIEEE C37.90a-1974. 

9. F.A. Fisher and F.D. Martzloff, "Transient Con

els, A Proposal for Insulation Coordination 

Voltage Systems," IEEE PAS-95 (11, pp

(JanuaryIFebruary 1976). 

10. Transient Voltage Suppression Manual, Chapter 2

Electric Company, Auburn, NY, pp. 13-17 (197

11. Transient Voltage Suppression Manual, Chapter 2

Electric Company, Auburn, NY, p. IS (1978). 

12. F.D. Mzrtz!e!?', "Transien: Oveivoltage Proieci

Implications of New Techniques," Pror, 4!!! S

and Technical Exhibition on Electromagnetic Com

Zurich, Switzerland, pp. 505-510 (March 1981). 

13. F.E. MaiizioiT, "Coordination of Surge Prot

Low-Voltage AC Power Circuits," IEEE PAS

pp. 129-133 (JanuaryIFebruary 1980). 

14. "Test Specifications for Varistor Surge-P

Devices," IEEE Sfd C62.33, 1982. 

15. E. Carroll, " Transient Attenuation with Metal Ox

tors for AC Mains Powered Equipments," pres

"Comel," University of Twente, Hollan

vember 1980). 

16. Transient Voltage Suppression Manual, Chapter 4, 

Electric Company, Auburn, NY, pp. 39-41 (1978

17. Longitudinal Voltage Surge Test #3, Code o

Regulation, Section 68.302(e), Title 37, Teleco

tions, Washington, D.C., U.S. Government 

Office. 1977. 

Franpis D. !$ler!z!e!T !M'5

born in Fiance, and rece

undergraduate degree at th

- SpCciaie ve ~Ccani

E'E!ectricit& ia 1951 ; he 

the MSEE degree from 

Tech in 1952 and the MSIA 

from Union College in 197

Since 1956 he has been 

General Electric Company

he - gained exoerience in the Transformer and Sw

Divisions. Upon joining General Electric Corporate 

and Development in 1961, he became involved 

semiconductor circuits and overvoltage protection. 

participated in the introduction and application of me

varistors since 1971. 

In IEEE, Mr. Martzloff is active on the Surge P

Devices Committee. He is chairman of the Workin

on Surge Characterization in Low-Voltage Circuit

also a member of the Ad Hoc Advisory Subcommitt

USA Advisory Committee on IEC SIC 28A and A

Subcommittee on Lw-Vakage S~ige Piotective I?w

has been awarded 10 U.S. patents, primarily in th

varistors and transient protection. 
CASCADING

SURGEPROTECTIVE

DEVICES:

COORDINATION

VERSUS

THE IEC 664

STAIRCASE
Significance 

Part 8 – Coordination of cascaded SPDs 

The early nineties were marked by the emergence of concerns about the coordination of cascaded SPD in the mi

of “common wisdom” that voltage surges impinging upon the service entrance of a building would inherently bec

less severe as they propagate and divide among the branch circuit of the installation. That perception was reinfor

by the publication in 1980 of an IEC Standard on insulation coordination that figured prominently a “staircase” of 

descending surge voltage levels. As a result of that perception, proposals were made to provide a service entran

SPD with a limiting voltage higher than the limiting voltage of the SPDs installed at the point-of-use receptacles. 

Numerical simulations and measurements on actual SPDs demonstrated the pitfalls of that perception. For an 

effective coordination to occur – service entrance SPD diverting the bulk of the surge current and point-of-use SP

mitigation as needed – the service entrance SPD cannot have a substantially higher limiting voltage than the poin

use SPD, lest the latter take on the bulk of the energy. The inductance of the wiring between the service entrance 

can add some voltage drop between the two devices, so that an acceptable degree of coordination can still be 

achieved if the two device have equal limiting voltages. 

The redeeming effect of the wiring inductance is of course dependent upon the waveform of the impinging curren

surge, as well as the length of the branch circuit. The relationships of these parameters are explored in the 

computations and experiments reported in the paper. 

Filename: Coordination 1991 
Cascading Surge

Protective Devices: Coordination versus the IEC 664 Staircase 

Montage en cascade de parafoudres: Coordination ou gradins IEC 664 ? 

Fran~ois D. Martzloff 

National Institute of Standards and Technology 

Gaithersburg, Maryianci 20899 

Jih-Sheng Lai 

Power Electronics Applications Center 

Knoxville, Tennessee 37932 

Abstract - CaCiiuAing ~lt.0 ,~,o;-e s;irge-pi-o;efiiiie 

devices located rpy~cti~~ly rrt the serl@ce e!!~mce c>f CI 

building ar~d near the sensitive equipment is intended to 

ensure that each device shares the surge stress in an 

manner commensurate with its rating, to achieve reliable 

protection of equipment against surges impinging fi-om 

the utility supply as well as internally generated surges. 

However, depending upon the relative clamping voltages 

of the two devices, their separation distance, and the 

waveform of the impinging surge, coordination may or 

may not be effective. Ihe paper reports computations 

confirmed by measurements of the energy deposited in 

the devices for combinations of these three parameters. 

Introduction 

Recent progress in the availability of surge-protective 

devices, combined with increased awareness of tine need 

tc -*nt~,t PPI.'.;~;.,~. rill..;..---* ---:-A ylvrvrr ovuirarnve qulyluurr agaluar SiiigeS, 

prompted the app!ication of 2 m~!ti-step ~SCX!~ 

protection scheme. In this scheme, a high-energy surgeprotective device is installed at the service entrance of a 

building to divert the major part of the surge energy. 

Then, surge-protective devices with lower energyhandling capability and lower clamping voltage than that 

of the service entrance, are installed downstream near.or 

at the equipment and complete the protection. 

To make the distinction between these two devices, we 

will call the service entrance device 'arrester' and the 

downstream device 'suppressor'. Such a scheme is 

described as 'coordinated' if, indeed, the device with 

high energy handling capability receives the largest part 

of the total energy involved in the surge event. 

P a0111111ilii%? - ie nlortiage e11 cnscnde de piu

,~grgJ~~2dzs, rez7ec;.iye::;e;;[ & !'o;.Fiv& sec;eG;- 

voisinage du mnrtriel ri prottger est envisqt dnm 

d'assurer que chnque dispositifprenne une part 

contrainte totale associte au transitoire qui corres

bier1 ci la valeur norninale de chacun. Cette disp

permet d'assurer la3abiliti de la protection con

transitoires d'origine exttrieure aussi bien que 

produits par le mattriel adjacent. Cette commun

donne les r&sultats de calculs, confzrmts pa

mesures, pour un ensemble de niveaux d'&c

relatifs, de distances stparant les dispositifs, et 

forme d'onde postulte pour le transitoire. 

This scenario was initially based on the technol

secondary surge arresters prevailing In the 197

early 1980s, as well as on the consensus concern

waveform and current levels of representative lig

surges impinging on a building service entrance. 

the emergence of new types of arresters for 

entrance duty and the recognition of waveform

greater duration than the classic 8/20 p impulse, 

situation arises that may invalidate the expectati

the cascade coordination scenario. 

Service entrance arresters were generally based 

combination of a gap with a nonlinear varistor el

the classic surge arrester design before the adv

metal-oxide varistors (MOV) that made gapless ar

possible. With a gap plus varistor element, the 

entrance arrester could easily be designed with a 

Maximum Continuous Operating Voltage (MCOV

120-V (rms) system. The downstrean suppresser
selected with a low level, driven by the perception that 

sensitive equipment requires a low protective level 

[I]. The scheme can work if there is a series 

impedance (mostly inductance) between the arrester and 

the suppressor, because the inductive drop in the series 

impedance, added to the clamping voltage of the 

suppressor, becomes high enough to sparkover the 

arrester gap. Thereafter, the lower discharge voltage of 

ihe arrester (made possibie by the gap) ensures that the ,.,. -,A -F rL- IIBaJw. put "k rurj giiige energy is diverted by the 

arrester, relieving the suppressor from the heavy duty 

121. 

This concept was in complete harmony with the 

'Installation Category' concept of IEC Pub 664-1980 

[3] which featured a descending staircase of voltages, 

starting with the 'uncontrolled situation' at the building 

service entrance, with several lower levels within the 

building (Figure 1). The lower levels would be 

achieved, according to IEC 664, by means of the natural 

attenuation caused by the multiple branch circuits, or by 

a deliberate interface - a surge-protective device. 

I I 

Category N 111 II I 

Figure 1 

Installation Categories according to 

!EC Pc;b 664-1 983 [3j 

On the other hand, the ANSIIIEEE C62.41-1980 Guide [4] 

(updated as a Recommended Practice in 199 1) defined a 

set of 'Location Categories' within a building. 

According to that concept, constant voltage levels are 

maintained downstream of the service entrance, but the 

current levels decrease. That concept was based on 

recognition that the wiring inductance would decrease 

the available surge current at locations deeper into the 

building - for the 8/20 ps current waveform then 

universally postulated to be representative. Thus, the 

stage was set for a mind-set of decreasing surge energy 

as the wiring progresses through the building, away 

from the service entrance. 

The new situation 

With the emergence of MOV-based, gapless arres

a new situation has been created. The Maxim

Continuous Operating Voltage of the arrester 

determine its r.!amping !eve!. Snm 3ti!i!ies wis

ensure survival of the arrester under the condition 

lost neutral, that is, twice the normal voltage f

single-phase, three-wire service connection. For th

phase systems in which devices are connected betw

phases and ground (protective earth), the usual prac

is to rate these devices for the line-to-line voltag

order to provide for the case of one comer of the 

being at ground, or the case of undefined vol

between neutral and ground. 

This survival wish is a motivation for selecting 

arrester clamping voltage corresponding to 1.7 

times the single-phase voltage. Meanwhile, if sin

phase equipment, typical of home electronic sys

('domotique' in French) are perceived to be sensi

there will be a tendency to protect them with the lo

possible clamping vn!hge. 

This sikatim sets the stage L- 1~~ 'U:-I T LlIgII-L

combination where the arrester c!amping w!@e 

higher than that of the suppressor [51. During 

ascending portion of a relatively steep surge such a

8/20 ps, the inductive drop may still be sufficien

develop enough voltage across the terminals of 

arrester and force it to absorb much of the impin

energy. However, during the tail of the surge, 

situation is reversed; the inductive drop is now neg

and thus the suppressor with lower voltage, not 

arrester, will divert the current. 

For the new waveforms proposed in C62.41-1991 

this situation occurs for the 10/1000 ps where the 

contains most of the energy, and the relief provide

the arrester might not last past the front part of 

surge. An alternate means has been propose

'hw-HigY where the arresfer c!m~phg w!hge is lo

than that of the suppressor [7],[8!. Thus

disagreement has emerged among the recommendat

for coordinated cascade schemes: the 1970-

perception and Ref [5] suggesting a 'High-Low' and 

new 'Low-High' suggestion of Refs [7] and [8]. 

This paper reports the results of modeling the situ

created by the emergence of gapless arresters and lo

waveforms, with the necessary experimental valida

These results cover a range of parameters to defin

limits of a valid cascade coordination, and will serv

input to the surge protective device application gu

now under development by providing a reconciliatio

the apparent disagreement, which is actually roote

different premises on the coordination parameters. 
MOV Circuit Modeling 

The current-voltage (I-V) characteristic of a MOV has 

long been represented by a power law, i. e., I = k VOL 

191. This equation is only applicable in a certain 

vo!kge (ccrrent) ra~g:: in wkd& the 1-V chl;rac&i;ls:ic 

presents a linear relationship in a Ing-!ng ~!nt. Fnr he 

high-current region of the characteristic, the current 

increment rate starts dropping. This change appears on 

the I-V plot as a voltage upturn in the high-current 

region. A modified I-V characteristic is proposed here 

as expressed in (1). 

~=k~cre-(V-Vo)[X-!:(V-Vo)l (1) 

The coefficients in (1) can be obtained from a curve 

fitting technique by minimum-error-norm [lo] using 

a MOV data book [9] or experimental results. The 

parameter k and exponent a can be obtained from fitting 

the data in the linear log-log region. The exponential 

term is added to cover the voltages higher than a 

threshold voltage Vo where the upturn begins and can be 

obtained frnm fitting the I-V chz~zcteT;Isti~~ i:: !he higher 

current (voltage) region. Using (11, the MOV circuit 

model can then be simply represented by a voltagedependent current source. 

Model parameters in (1) can be obtained from the MOV 

data book and verified by experiments. The exponent ar 

in this model is a function of the MOV voltage rating. 

The threshold voltage Vo and coefficients X and { are 

.functions of the voltage rating and the size. Table 1 lists 

the curve fitting data for the equivalent circuit 

parameters of three MOVs typical of what might be 

considered for a 120-V power system: 130 V for 'low', 

150 V for 'medium', and 250 V for 'high'. For 

European systems with a 220-V single-phase voltage, 

similar ratings would be 250 V for a 'low', 320 V for a 

'medium', and 420 V for a 'high'. Note that the 

numerical values of the parameters are unitdependent, 

and are given in Table 1 for units in volts and amperes. 

Table 1 

Curve fitting results for three 20-mm dia MOVs 

Rating I k a A I < IVOCV) 

130 V )4.0*10-'~ 1 30 10.051 18.10.~ 1 320 11 

In Figure 2, the marked points are the data directly read 

from curves in the MOV data book, while the three linesare a plot of the computed I-V characteristic &cording 

to (I), using the parameters listed in Table 1. Note the 

remarkable fit achieved by this model over the range of 

interest. 

I : : ::::::I : :::::::I . . 111 ..................... lWI '' ! ' " ! ' -' 

o.oi 0.1 t 10 100 1000 

Peak Currenl (A) 

Figure 2 

MOV characteristics obtained from model

results 

There is a tolerance of f 10% on the actual 

within a given varistor rating. Figure 2 show

maximum clamping voltage levels; a device at th

end of the tolerance band would have a charact

20% lower than the data book characteristics. In 

the two closely rated cascaded devices (130 V an

V) could in some extreme cases become inverted 

sequence, 'Low-High' becoming in reality 'High-

as 130 x 1.1 = 143 and 150 x 0.9 = 135. 

Furthermore, results (presented below) show that f

250-150 combination, the difference is so large 

low-end 250 (225 V) combined with a high-end 15

V) would not make an appreciable difference 

energy sharing. Thus, the simulation computation

performed for all three devices at their nominal v

with appropriate modification of the parameters 

model equation. 

Simulation of Cascaded Devices 

in a Low-Voltage System 

Figure 3 shows a typical two-stage cascade 

protection. The arrester and the varistor are sep

by a distance d determined by the specific install

- Location Location 

Categoty B Category A 

Figure 3 

Configuration of a two-stage cascade 
Four different d values, 5 m, 10 m, 20 m, and 40 m 

were used in the simulation, with a #12 AWG (1.83-mrn 

dia.) wire, representative of U.S. practice for 20 A 

branch circuits. At the frequencies involved in the 

surges considered, inductance is the dominant parameter 

and the wire diameter plays only a minor role [Ill; 

so that the resistance of the wire could be neglected. 

However, given the flexibility of the model, it was 

inciuded. 

The complete simulation model, shown in Figure 4, 

consists of a surge source IG, two voltage-dependent 

current sources IA and IS, and a line impedance between 

the two current sources. For three device voltage levels, 

there is a total of nine possible cascade combinations as 

shown in Table 2. 

Table 2 

Nine cascade combinations for three devices 

Arrester 

130 V 

250 V 

150 V 150 V 

i30 v 

Two standard waves from Ref [6] were chosen: the 

1.2150 ps - 8/20 ps Combination Wave, and the 10/1000 

ps Impulse Wave. For four distances, two waveforms, 

and nine cascade combinations, a total of 72 cases are 

reported here. The case of the 100 kHz Ring Wave was 

also simulated and tested [12], but is not reported 

here because the low energy stress involved in that 

waveform will not deposit substantial energy in the 

SrippSSOr or the arrester. 

Simulation and Experimental Results - 8/20 Wav

As one example of the combinations that w

simulated, consider a cascade with 250 V and 13

devices separated by 10 m. The simulation result

the currents flowing in the two devices are show

Figiire 5, where it is the iotai current injected into 

cacade bj !he surge souice of the ~~odei, il is 

arrester currentj and I- is the suppress=: cum

L 

Figure 6 shows the corresponding device clamp

voltages, V1 and V2 across the arrester and suppre

respectively. Figure 7 shows instantaneous powers 

and P2, respectively for the arrester and the suppres

By integrating the instantaneous power, the ene

deposited in the arrester and the suppressor w

calculated as 29.7 J and 8.6 J respectively. 

Figure 5 

Simulated current responses for 250 V - 130 

cascade, 10 m separation, 8/20 ps applied su

Figure 6 

Simulated voltage responses for 250 V - 130 

cascade, 10 m separation, 8/20 ps applied su

Figure 7 

Simulated dissi~ated Dower for 250 V - 130 

cascade, i 0.m sedaration, 8/20 ps surge 
Table 3 lists the computed results for the 8/20 Wave 

simulation, as energy deposition in the arrester (A) and 

suppressor (S) for all the combinations of different High 

(250 V), Medium (150 V), and Low (150 V) devices as 

arrester and suppressor. 

Table 3 

Energy deposition in the cascaded devices 

with a 3-kA 8/20 Wave as the surge source. 

Energy deposited in each device (joules) as a 

Rating of I function of separating distance (meters) 

vice 

I I II A '"I S I AISIAISIAIS 

Figure 8 shows in graphic form the results of Table 3, 

where the lines represent the energy deposited in the 

suppressor as percentage of the total surge energy, as a 

function of relative clamping voltages and separation 

distance. With the scale used in the figure (geometric 

distance), the curves are approximately straight lines 

over the range. For the High-Low condition, the energy 

deposition in the suppressor decreases rapidly when the 

separation distance increases. This result explains how 

the High-Low configuration can achieve a good 

coordination with the 8/20 Wave, provided that there be 

sufficient distance between the two devices, as stated in 

Ref [5]. 

When the distance between two devices Is reduced, the 

energy deposition tends to increase in the suppressor and 

decrease in the arrester. This decrease occurs because 

the line inductance does not provide enough voltage drop 

(L dildr), and the low clamping voltage of the suppressor 

reduces the voltage across the arrester, and thus reduces 

the energy deposition level. The total energy deposition 

in the two devices also varies with the distance for the 

High-Low configuration. In Table 3, the total energy 

deposition for the 250-250 combination is near constant 

at 103 J for different distances. However, for 250-150 

and 250-130 combinations, the total energy deposition 

decreases when the distance is reduced, because the 

suppressor tends to lower the voltage across the arrester. 

This situation can be explained by the fact that the 

impinging surge is defined as a current source, so that 

offering it diversion through a device with higher 

clamping voltage results in higher energy deposition. 

H-M 

H-L \ 

5 10 20 4

DISTANCE BETWEEN ARRESTE

AND SUPPRESSOR (m) 

Relative energy deposited by an 8/20 ps Wa

in the suppressor for arrester-suppressor 

combinations of 250 V (HI, 150 V (MI, or 1

!L! ratings, as a flrncfin ~f separation distm

For Low-High configurations such as 150-250 

130-250 cases, the higher voltage suppressor rec

ahiost zeio energy. Tine use of the suppressor is 

redundant in this case, except for its applicati

mitigate internally generated surges. With closely 

devices (130-150), the 150-V voltage suppressor 

receives much less energy than the 130-V arrester

Now turning to measurements, the same ca

configuration, 250 V - 130 V with 10-m sepa

(Figure 3), was injected with a surge produced 

Combination Wave generator. The surge gen

delivers an approximation of the standard wave

consequently, the waveforms obtained from 

experiment are not exactly the same as the sim

waveforms. However, the power distribution be

the two devices shows good agreement betwee

simulation and the experiment. 

Figure 9 shows the experimental results obtained w

cascade of two devices, 250 V and 130 V, with 10 

separation. Oscillograrns were recorded for the cu

voltage and power in the two devices, wher

subscript 1 corresponds to the arrester and the sub

2 to the suppressor. The goal was to produce a 

impinging surge (I1 + 12), but a slightly higher cu

(3.3 kA instead of 3 kA in the simulation) 

produced, typical of the sensitivity of nonlinear ci

to minute changes in the applied voltage. The e

deposited in each device was computed by integrat

the power (performed by the oscilloscope): 33.8 J 

arrester and 11.1 J in the suppresso~ To com

simulation and measurement, prorating the simu

results (from Figure 7) to 3.3 kA would yield 32.7 

nz~ Y.J J respeciiveiy, a satisfactory agreement. 
1, + 12: 1000 Aldiv 

Il : 1000 A/div 

(a) Arrester 

It + 12: 1000 Aldiv 

12: 1000 Aldiv 

(b) Suppressor 

Figure 9 

Experimental results for the 250 V-130 V, 10-m 

apart cascade condition. 

Compared to the 8/20 Wave, the 1011000 Wave has a 

slower and longer drooping tail that contains most of the 

surge energy. During the long tail period, the inductive 

voltage drop between the arrester and the suppressor is 

low, and the voltage appearing across the arrester is 

reduced by the effect of the suppressor even with long 

distances between the two devices. Thus, the High-Low 

configuration cannot be coordinated as the high-voltage 

arrester will not absorb any impinging energy, but the 

suppressor does. Figures 10, 11 and 12 show the 

computed current, voltage, and power for the arrester 

and for the suppressor under a High-Low (250-130) 

simu!ation f~; a 2%-A p~k mge aneiii. 

The high-voltage arrester clamps the voltage during 

impulse rising period and draws a small amount of 

current pulse, 11, which is almost invisible in 

computer-generated plot of Figure 10. The po

dissipated in the arrester, PI, is also a small pulse 

appears at the rising period as shown in Figure 12. 

low-voltage suppressor absorbs all the impinging ene

in this High-Low configuration, defeating the inten

coordination. 

0 0.2 0.4 0.6 0.8 1 12 1.4 1.0 1.8 

t (m) 

Figure 10 

Sirnuiated current responses for 250 v - 130 

cascade, ? 0 m separation, ?0/? 005 i;s sijig

0 0.2 0.4 0.6 0.8 1 12 1.4 1.8 1.8 

t (m) 

Figure 11 

Simulated voltage responses for 250 V - 130 

cascade, 10 m separation, 1011 000 ps surg

0 0.2 0.4 0.6 0.8 I 12 1.4 1.6 1.8 

t (a) 

Figure 12 

Simulated dissipated power for 250 V - 130 

cascade, ! C! .rl? separatlen, ! 0/! 000 ;.s surg
Table 4 lists the simulated energy deposition in the 

cascaded devices for different High-Low and Low-High 

combinations and for different distances. Figure 13 

presents in graphic form the results of Table 4, with 

lines showing the energy deposited in the suppressor as 

percentage of the total surge energy, as a function of 

relative clamping voltages and separation distance. 

iabie 4 

Energy deposition in the cascaded devices \i*iih 

a 220-A, 1011 000 Wave as the surge source. 

Energy deposited in each device (joules) as a 11 Rating of 1 function of se~aratina distance (meters, 

H-L 

H-M 

40, L-L 

M-H I I I L-H 

DISTANCE BETWEEN ARRESTER 

AND SUPPRESSOR (m) 

Figure 13 

Relative energy deposited by a 1011 000 ps Wave 

in the suppressor for arrester-suppressor 

combinations of 250 V (H), 150 V (MI, or 130 V 

(L) iaiiiigs, as a finction of separation distance 

It can be seen from Table 4 that the lowvoltage d

always absorbs higher energy than the high-vo

device. This situation exists because the voltage a

the high-voltage device is clamped to the same lev

that of the low-voltage device, and thus the ener

diverted to the device having the lower clamping vo

of the pair. 

Unlike the case of the 8/20 Wave, coordination fo

1011000 Wave can only be achieved by Low-H

Medium-High, or Low-Medium. Equally rated de

(250-250, 150-150, and 130-130) result in 50 % o

surge energy being deposited in the suppressor, 

very good coordination. Note that with two devic

equal nominal value, but random tolerance levels

possible that the relative tolerances might in fact pro

a situation which would not achieve good coordina

for instance, an effective 150-130 combination can 

from tolerance shifts in an intended 150-150 or 13

pair. This shift would impose a 70-5 duty to 

suppressor and only 7 J to the arrester, in the ca

5-m separation. 

The exprim%! respcxse te a !O!- WXW, 

Low-Medium configuration is shown in Figure 14 w

I, and I? are the currents flowing in the 130-V ar

aid the-150-V suppressor respectively. This f

shows an example of good coordination 

Low-Medium, where most of the surge energ

absorbed by the low-voltage arrester, and little 

current propagates into the building - one of the go

the two-step coordinated approach. The arrester vo

V1 is almost the same as the suppressor voltage V2 

a slight difference at the beginning of the surge. 

I,: 1000 A IAi,. -,-a. 

I,: 1000 

~/div 

v,: 200 

Vldiv 

v2: 200 

Vldiv 

Figure 14 

Experimental results for a 130 V - 150 V, 1

apart cascaded corrdition with ! C!! 000 Wa
Discussion 

The benefit from a coordinated approach is to allow a 

single device at the service entrance to perform the 

high-energy duty, while several smaller devices within 

the premises can perform local suppression. This 

arrangement avoids !he flow nf !arge surge currmh il 

the branch circuits of the installation, a situation known 

to produce undesirable side effects [13]. 

On the other hand, the situation exists where millions of 

small suppressors have been installed within equipment 

or as plug-in devices, with only sporadic and anecdotal 

reports of problems. Thus, it is evidently possible to 

obtain protection with suppressors alone, while a 

coordinated scheme would provide additional benefits 

and eliminate side-effects. 

Some utilities wish to provide a service-entrance arrester 

capable of withstanding the 240-V overvoltage that can 

occur on the 120-V branches when the neutral is lost. 

This desire will force the coordination scheme into a 

High-Low situation because of the uncontrolled 

installation of low clamping voltage suppressors by the 

ocmpr;?: of the piiiises. The resiiits of the simuiation 

aid experirnenh! measurerr.ents shes... that the ~bjective 

of coordination could still be achieved with a 250-130 

combination, as long as some distance is provided 

between the two devices, and as long as long waves such 

as the 10/1000 pi are not occumng with high peak 

values. This proviso provides an incentive for obtaining 

better statistics on the occurrence of long waves. 

ANSIIIEEE C62.41-199 1 [4] recommends considering 

these long waves as an additional, not a standard 

waveform. Thus, the determination of a successful 

coordination depends for the moment on the perception 

of what the prevailing high-energy waveforms can be for 

specific environments. 

Conclusions 

1. Coordination of cascaded devices can be achieved 

under various combinations of parameters, but some 

combinations will result in having a suppressor with low 

energy-handling capability called upon to divert the 

largest part of the surge energy. This uncoordinated 

situation can create adverse side effects when high 

current surges occur. 

2. Significant parameters in achieving successful 

coordination involve three factors, over which the 

occupant of the premises has no control: the relative 

clamping voltages of the two devices, their separation 

distance, and the prevailing waveforms for impinging 

surges. This uncontrolled situation presents a challenge 

and obligation for standards-writing groups to address 

the problem and develop consensus on a trade-off of 

advantages and disadvantages of High-Low versus 

Low-High. 

3. Coordinated schemes can be proposed by utiliti

their customers, including a service entrance arrester 

one or more plug-in devices to be installed for 

dedicated protection of sensitive appliances. How

even such an engineered, coordinated arrangement c

be defeated by the addition of a suppressor with a 

low clamping voltage, not an insignificant likelihoo

view of the present competition for lower clam

voihges. 

REFERENCES 

Martzloff, F. D. and Leedy, T. F., Sele

Varistor Clamping Voltage: Lower Is Not Be

Proceedings, 1989 Ziirich EMC Symposium. 

Martzloff, F. D., Coordination of Surge Prote

in Low-Voltage AC Power Circuits, I

Transactions PAS-99, JanuaryIFebruary 1980

129-133. 

IEC Publication 664-1980 Insulation coordin

within !ow-vc?!hge systems, ir\.cludir?g c!arm

and creepage distances for equipment. 

lEEE C62.41-1980, IEEE Guide on Swge Vo!t

in Low-Voltage AC Power Circuits. 

Stringfellow, M. F. and Stonely, B. 

Coordination of Surge Suppressors in Low-Vo

AC Power Circuits, Proceedings, Open Forum 

Surge Protection Application, June 199 1. 

IEEE C62.41-1991, IEEE Recommended Pra

on Surge Voltages in Low-Voltage AC P

Circuits (To be published September 1991). 

IEC 64lWG3 138A, Explanation of interface

overvoltage categories - Supplement to Append

of Report 664, November 1990. 

Standler, R. B., Coordination of Surge Arre

and Suppressors for Use on Low-Voltage M

Proceedings, 1991 ZGrirh EMC Syrr?psium. 

Trmsient V=!kge &ppieasioii Eevices, E

1991. 

[lo] Luenberger, D. G., Linear and Nonl

Programming, Addison-Wesley Pub. Co., Rea

Massachusetts, 1984. 

[ll] Martzloff, F.D., On the Propagation of Old 

New Surges. Proceedings, Open Forum on S

Protection Application, 1991, pp 19-28. 

[12] Lai, J.S. and Martzloff, F.D., Coordin

Cascaded Surge-Protective Devices, Proceed

IEEEIIAS Annual Meeting, October 1991. 

[13] Martzloff, F. D., Coupling, Propagation, and 

Effects of Surges in an Industrial Building W

System, IEEE Transactions IA-26, MarchI

19%, pp. 193-203. 
CASCADING

SURGEPROTECTIVE

DEVICES:

OPTIONS FOR

EFFECTIVE

IMPLEMENTATION
Significance 

Part 8 – Coordination of cascaded SPDs 

The early nineties were marked by the emergence of concerns about the coordination of cascaded SPD as the 

concept of “Whole-house protection” was gaining popularity. However, it appeared that the selection of service 

entrance SPDs and point-of-use plug-in SPDs was not an integrated process, hence some possibility that the 

expected coordination might not be achieved. On the other hand, if a well-designed combination could be 

implemented by a single authority responsible for the selection of the two devices, then the competing requiremen

for these to devices might be accommodated. 

The service entrance SPD is generally selected from the point of view of the utility, and therefore tends to be a 

rugged device with relatively high limiting voltage because of the desire to have a conservative maximum continuo

operating voltage (MCOV). On the other hand, the point-of-use SPDs, for those purchased independenly from th

service entrance SPD, are generally designed to offer the lowest possible limiting voltage. This relationship make

coordination difficult. If the two devices are selected with the same limiting voltage (and thus comparable MCOVs

then the inductance separating the two devices can have a chance to decouple the two devices sufficiently to ach

a satisfactory coordination. The inductance of the wiring between the service entrance can add some voltage dro

between the two devices, so that an acceptable degree of coordination can still be achieved if the two device have 

equal limiting voltages. The redeeming effect of the wiring inductance is of course dependent upon the waveform 

the impinging current surge, as well as the length of the branch circuit. 

In this paper, the relationships of these parameters are explored by numerical simulations. Cross-validation of 

simulation and measurements in actual circuits for typical applied surges was demonstrated in earlier papers so it 

was not repeated here. 

Filename: Coordination 1992 
Franpis D. Martzloff 

National Institute 

of Standards and Technology t 

Gaithersburg MD 

Jih-Sheng Lai 

Power Electronics A-pplications Center 

Knoxville TN 

asti& - ba-k- && 'T&+aT par- JOT a 

successfir1 coordination of cascaded surge-protective devices 

include the rehive volrage clamping of the two devices, 

their electrical separation through wiring inductance, and 

the actual wave$onn of the impinging surge. The authors 

euunine in detail the implications of the situation resulting 

from the present uncoordinafed applicorion of devices with 

low clamping voltage a the end of branch circuits and 

de""k"&" .&k +GyLwT ch.@Eg vc&ge &. :he scs"-k-e 

emance. As an alrernatr've, several options are oflered for 

discussion, that might result in gective, reliuble 

implernentution of the cascaded protection concept. 

Ccordinating cascading surge-protective devices is a 

concept whereby two devices are connected at two different 

points of a power system, with some physical, but mostly 

electrical, separation (inductance) between the two points. 

The upstream device is designed to divert the bulk of an 

impinging surge, while the downstream device, close to the 

equipment to be protected, is intended as a final clamping 

stage, including surges generated within the facility. 

Successful coordination is achieved when the heavyduty 

upstream device does indeed divert the bulk of the surge, 

rather than letting the downstream device attempt to divert 

a emsive moiiili of &e -urge cLUreni. TO &-,&j,, 

between the two surge-protective devices (abbreviated as 

'SPD'), the heavy-duty, upstream device will be referred to 

as 'arrester', while the lighter duty, downstream device will 

be referred to as 'suppressor'. The basic and critical parameters for successful coordination of the arrester-suppressor 

cascade include the relative voltage clamping of the two 

devices, their electrical separation through wiring h&ciC~m*, md C&e xtui -w-B'v-e fo- of -he hphging surge* 

The prime objective of a cascade anrangement is to 

maximize the benefit of surge protection with a minimum 

expenditure of hardware. Another benefit of a cascade is 

the diversion of large surge currents at the service entrance, 

so that they do not flow in the building, thereby avoiding 

side effects (Martzloff, 1990). * 

* Citakm.. nreprese.@ed nr (4uthr, Dae) r&er thnn 5~ n~ehered 

it-, and are listed a&habeticaliy in the appended bibliography. 

7he bibliography ah includes ifem not cited in this paper, as on 

indication of the increaring level of inrerest in tfi subject. 

Technology Administration, U.S. Dcpment of Commerce 

2oniriouiions oi iho i&tionai insiiiurc of Standards and iec-moiogy are not subject to U.S. Copyright 

Tine idea of a two-step protection has been exp

many authors over the last two decades, as can be 

the bibliography included in this paper. Startin

different premises, and with changing opportunitie

technology evolved, these authors have reached conc

that are sometimes convergent, and sometimes div

giving the appearance of contradictions. 

In two previous papers (Lai & Martzloff, 

?vrhrr~oE & hi, iWi j, we have examined rhe simp

of a two-wire, single-phase circuit where each of t

SPDs is connected between the high-side of the line 

low-side (neutral or grounding conductor), show

numerical examples the effect of three sig

parameters: relative clamping voltage, separatio

impinging waveform. When these three parameters 

taken into consideration, many of those earlier di

wiic1-~~i~lii~ iivonger appear contraaiicrory. Iiathe

become for each case a limited view of a consistent 

changes over the complete matrix of the possible ran

the three parameters. 

The two-wire circuit is a simplification applicabl

U. S . practice for residential service, which is ge

single-phase, with a mid-point neutral bonded to th

ground at the entrance to the building. In some co

a &ffcTBnw && ifi &,= pr&.e ',f pun&g: 

neutral is grounded at the distribution transformer bu

_mounded at the service enme- as we!. ?&

installation includes a distinct 'protectiveearth' co

that is bonded to the local earth ('ground' in U.S. E

not to the neutral. In contrast, US. practice is to b

local ground, at the service panel, both the neutral 

'equipment grounding conductor' that serves the 

&.-LA- -- cL- 6--&-~---- ---L> ~LV-U~G IUWW 45 ~l~i pu~~kuvt; arm in Eu

practice. 

This difference in the utiity -,u_cdbg p=ti,c

implications on the implementation of a cascade 

European context, where a service entrance arrester 

likely to be connected between the incoming lin

protective earth, while end-ofcircuit suppressors ar

iiiceiy TO be comecteci between he and neutral. 

;iligezissiii 3s more ~mpi~~ than ibe simpie tw

cascade corresponding to the US. practice, and we p

a model that takes into m~idepAn~ txs mrp c

circuit. In the unbonded neutral connection schem

is a greater separation between the two cascaded devi

thereby the likelihood of successful coordination 

expected to increase. 
It is one thing to design an approach based on opthum 

coordination where all the parameters are under the control 

of the designer. Such an opportunity existed in utility 

systems implemented under centralized engineering. It is an 

altogether different challenge to attempt, after the fact, 

coordinating the operation of surgeprotective devices 

connected to the power system by diverse and uncoordinated 

(and uninformed) users. For example, excessively low 

clamping voltages may be a threat to long-tenn reliability of 

varistors (Markloff & Leedy, 1987; Davidson, 1991). 

Our effort in promoting a coordinated approach may 

come too late for the de facto situation of having millions of 

suppressors in service with a relatively low clamping 

voltage. This situation will impose an upper limit to the 

clamping voltage of a candidate retrofitted arrester. 

Therefore, close attention must be paid to the selection of 

the reiative ciamping voitage of the two devices, in view of *L- ---n:A-- -----:-----a- c-- --L LUG wruuc;uug rajuucucuw rur pcrlulluarcu uuucr surgc 

conditions - a successful cascade - and reliable withstand 

for temporary power-frequency ovemoltages. Nevertheless, 

coordination might still be achieved through understanding 

the possible tradeoffs; in the future, users could avoid the 

pitfalls of poor coordination or the disappointment of 

implementing protection schemes that cannot provide the 

hoped-for results. 

Finally, we propose for discussion among utilities and 

manufacturers a diffkent approach to the selection of the 

service entrance arrester: a one-shot expendable device that 

would protect the installation against rare, but catastrophic 

sustained temporary overvoltages at power frequency. 

c: ---- 1 --A - LA- AK--l-ax a T -2 1 Ml\ :IL--&- rrgurca I auu A, uulu (lvmxu~urr OL ~*ll, 177~)~ uiuuac 

the impact of the relative voltages on the energy sharing 

between the two devices. In these two figures, a plot is 

shown of the percentage of the total energy dissipated in the 

suppressor, as a function of the distance separating the two 

devices, for various combinations of clamping voltages, and 

for two postulated waveforms. In the plots, H, M, and L 

correspond respectively to a high, medium, and low voltage 

rating, in the context of a 120-V rms circuit application. 

As long as the only postdated impinging wavefonn 

remained the classical 8120-ps current surge (Figure I), 

good coordination could be expected, even with an arrester 

clamping at a voltage somewhat higher than the clamping 

v&ge of the sqqrmwr- ghg~g~phy wm ~rpi~~ 

in the development of several insulation coordination 

documents of the International Electrotechnical Cornmission (IEC) in the last decade (Crouch & Martzloff, 

1978; Martzloff, 1980; IEC 28AvSA/Las Vegas109, 

1983 and its later modifications). 

5 10 20 40 

DISTANCE BETWEEN ARRE!STER 

AND SUPPRESSOR (m) 

Figure 1 

Relative energy deposited by a 3kA. 8120-p~ wav

in the suppressor for arrester-suppressor combinati

of 250 V (HI, 150 V (MI, or 130 V (L) ratings, 

as a function of separation distance 

However, if, in accordance with new descriptions 

surge environment, we apply a surge with longer wave

such as the 1011000 ps of ANSUIEEE C62.41-1991, 

German 101350 ps (Hasse et al., 1989), then coordi

cannot be obtained if the arrester has a higher cla

voltage than that of the suppressor (Figure 2). 

oc, I I , LH M-H

5 10 20 40 

DISTANCE Bl3WEN ARRESTER run c~ ~asacccna IA N." -r r -" p,, 

Figure 2 

Relative energy deposited by a 220A, 1011 000-ps w

in me suppressor for arrester-suppressor combinati

of 250 V (HI, 150 V (MI. or 130 V (L) ratings, 

as a function of separation distance 
A partial remedy might be expected in a scenario where 

the arrester and the suppressor would be specified with the 

same nominal (rms) voltage. The arrester would have, by 

definition, a larger cross-section than the suppressor, in 

order to fulfill its mission of prime dissipator of energy. 

The larser cross-section remltc in a !nwc c11mnt dsmity, 

lowering the clamping voltage com_~ared with that develo* 

for the same current into the suppressor experiencing a 

higher current density. Thus, we could expect some relief 

of the 50%-50% division of energy shown in Figure 2 for 

two &vices of equal voltage rating. 

To quantify this expectation, we have modeled a 40-mm 

diameter varistor rated 150 V rms, and used the model 

defined in our 1991 paper for a 20-mm diameter vzidsr. 

Figure 3 shows the I-V characteristics for the two devices. 

Starting with the same voltage at 1 mA (equal by definition 

of the nominal voltage), the 40-mm varistor indeed provides 

a siightly lower clamping voltage than the 20-mm varistor, 

for currents above 1 mA. Conversely, for the same voltage 

@aral1el connection), the plots show that in the 200-A range 

(the value selected for the 10/1000-ps wave in the 1991 

tests), there is a UX)/300 ratio in the currents flowing in the 

two devices. In the 3-kA range (the value shown in 

ANSIIIEEE C62.41 for the 8120-ps wave), the 2000/UX)O 

ratio is practically the same. 

QPOl MI Ll 1 10 1m 1om loo00 

Qrrent (4 

Figure 3 

Cuwe-fitting for the nominal I-V characteristics of 

1504 rated varistors. with diameters of 20 and 40 mm 

unequai saaring of the current for two paraiieiconnected devices with vertically offset characteristics is 

~enerallv Gew& m &stale sGsf.&bq cppti~q 0-----J 

when the objective is to increase the energy handling 

capabiity of the two devices connected at the same point. 

In the present case, however, the objective is opposite: a 

very unequal sharing is sought to effect coordination 

-between the two devices. 

Figure 4 shows a cascacie using the 40-mm varistor as 

service entrance arrester and the 20-mm varistor as surge 

su,n3ssnr. Th,e f pre &c mzeps =f !=ati~n 

categories (A and B) defined in ANSIIIEEE C62.41-1991. 

Figure 4 

Configuration of a two-stage cascade, with bath 

connected between line and neutral conducto

The arrester and the varistor are separated by a 

d! justifying the tramitinn frnm Cktpgcq B ?.f ~e 

entrance to Category A at the receptacle. 

In the numerical examples and computer-genera

illustrated below, we selected only one value, 10 m

the distance separating the arrester and the suppre

our referenced 1 99 1 papers, we gave examples of 

ranging from 5 to 40 meters, as well as plo

measurements of the surge currents in an actua

The correspondence kmen the made%g 

experimentk measurements was demonstrated 

papers. Therefore, for the similar combination o

discussed here, we can use the same numerical mo

appropriate modification of the device parameters), 

limit ourselves to modeling - precisely the point o

developed a valid model. 

Figure 5 shows the computed current division 

arrester (I:) and suppressor (Id for a 3-k-A, 8!2Q-

impinging upon a cascade of two varistors, 40 mm 

arrester and 20 mm for the suppressor, each rated 

Figure 6 shows the division for the same cascad

220-A, 10/1000-ps impinging wave. 

Figure 5 

Division of the current between arrester (I,) 

and suppressor iizj for a ? 50-V, 40-mmi20-mm ca

10-m separation, with a 3-kA, 8120ys impinging 
Figure 6 

Division of the current between arrester (Il) and 

EE~~DCEOI !!2! fey e ? 5°K ~dn-mr??!X!-mrr! rezcade, 

10 rn separation, 220-A, 1011 000-ps impinging surge 

Tnqection of these two figures also provides qualitative 

insight on the behavior of the circuit. For the 8120-ps 

wave, the inductance of the 10-m length of wire retards the 

rise of current in the suppressor during the first part of the 

surge, but tends to maintain the current in the suppressor 

even after the arrester current has decayed to zero. For the 

1011000-p wave, the wiring contributes a significant 

difference in the currents only during the rapidly-changing 

period - the front of the wave - with the difference in the 

tail solely attributable to the difference in cross-section 

between the arrester and the suppressor. 

Because of the quasi-constant voltage across the varistor 

&&-kg +&= p&-g= =..r=fi:, the -P, hhsvkr qpq is t&= 

pwer @a& of Fists 7 and 8 which show the power 

dissipated in each device, respectively for the 8120-ps surge 

and the 10/1000-p.s surge. The corresponding energy was 

obtained by integrating the two power curves. The results 

are shown in Table 1, which also includes the results for the 

original 20-mml20-mm cascade. 

Figure 7 

Division of the power between arrester (PI) and 

suppressor (P2) for a 150-V, 40-rnrn120-mrn cascade, 

10 rn separation, 3-kA, 8120-ps impinging surge 

Figure 8 

Division of the power between arrester (PI) and suppr

(P2) fw s ? 50=v, 40=m7:!2O=mm ccsc&e, ? O m sepz

with a 220-A, 1011 000-ps impinging surge 

Table 1 

Distribution of deposited energy in arrester and suppre

20mm120mrn and 40mrn120mrn cascades, 10 m 

separation, 8120-p~ and 1011 000-p~ impinging surg

Waveform Devices Arrester Suppressor Suppress

I I I Youles) I iioules) il% of to

Predictably, the 8120-p waveform produces a 

coordination, for a U)-d20-mm cascade as well as 

40-111111120-mm cascade. In fact, the only diffe

between the two is a fraction of joule, which is not s

in the table where the values have been rounded off. 

When postulating a 1011000-ps waveform, the 4

arrester indeed diverts slightly more current than the 2

suppressor, as shown in Figure 6. However, whe

energy levels are compared (see Table I), the improv

obtained by changing from 20-d20-mm to 40-mmlU

cascades is only a small reduction in percentage of the 

down to 40% from the 48% of the original 20-mm12

cascade. 

The small 8% advantage of the 40-d20-mm ca

is likely to be lost when the statistics of possible toler

for the two devices are considered. Figure 9 show

effects of combing the relative tolerance deviations 

nominal values, the same nominal values that were u

computing the advantage of the #mm/20-mm cascad

the 20-mm/20-mm cascade. 
Arrester 

High 

r 

Suppressor II Decreased I Low 

Arrester 

Suppressor 1) High 1 

Figure 9 

Advantage of 40-mm120mm cascade 

over 20-mm120-mm cascade 

For any cascade where the tolerances move in the same 

direction (50% of the cases), the advantage remains at 8 36. 

For combinations where the tolerances make the arrester 

lower than the suppressor (25 36 of the cases), the advantage 

is improved. For combinations where the arrester is higher 

than the suppressor (25% of the cases), the advantage is 

decreased and may be completely wiped out. Thus, the 

hoped-for improvement fbm the lower current density 

might not be very substantial. 

8% 

In polyphase systems, or even single-phase systems, the 

hndhg h.twe.3 3~~tmJ md P-&I @QQ=~) my & zt SOE~ 

distance from the arrester - at the limit, one might 

consider a system with ungrounded neutral or no neutral. 

In such cases, the arresters are likely to be connected line 

to-ground. Yet, the majority of suppressors are likely to 

be connected lineto neutral - the two conductors feeding 

the power port of the sensitive ioaci in need of surge 

protection. Indeed, some countries or some suppliers object 

tc my =the. rnCde =f m-a&ien fGr ~\~-ge-p4~>+~ bevim 

installed at receptacles or incorporated in connected 

equipment. Thus, the simple case treated in our 1991 

papers, with the two devices (arrester and suppressor) 

diverting the surge to the same neutral conductor, may be 

more complicated - perhaps with the welcome effect of a 

greater separation of the two devices. 

Figure 10, from (Rodet, 1992) shows a typical conn&don & agra f"r sY*m wi& a proktive 

earth distinct from the neutral. This configuration could be 

modeled for the complete circuit; however, as an illustrative 

example and for comparison with the case of Figure 4, we 

have simplified the circuit as shown in Figure 11. The two 

varistors have the same voltage rating (150 V). Of course, 

in a European context of a 230/400-V three-phase system, 

the modeling should be done with varistors of appropriate 

ratings, say, 32V V. The generic conclusions reached for 

the example of the typical single-phase 2401120-V in use in 

the U.S. can be extended to the 2301400-V situation. We 

interpreted the configuration of Figure 10 and postulated for 

Increased 

the coupling of the impinging surge as a com

scenario, that is, a surge coupled by earth cur

inductive coupling into the loop formed b

conductors and earth. I 1 2 

6 

P-__--__ #n-..~-~ -nn-s auu~ tie; \nuulaL, I YYL] 

LEGEND 

RB: Earth ground at the distribution transform

1 : Service entrance panel 

2: Sub-panel with feeders for branch circui

3: Local earth electrode (PE) 

4: Arresters connected to local earth (PE) 

5: Connection of arresters to PE 

6: Single-phase equipment that may contain 

Figure 10 

Typical threephase !nsts!!atIm w;th prcmF+;v

separate from the system neutral 

Figure 11 

siiipiifi& m&iici &,.ivd frm 

the three-phase system of Figure 10 

Inspection of this circuit model reveals that 

between the two devices of the original cas

longer the simple length of two-conductor wire

pinging surge, postulated to be common mod

revisited for such a power system configurati

two induced surge currents were exactly equa

common mode) and the two arresters were ide

voitages produced at points L and N by the su

flowing in each of the arresters would be equ

there would be no stress imposed upon the 

connected line-to-neutral at the end of the bran
For a voitage m appear between L and N, we must 

postulate unbalanced currents in the conductors L and N 

and a tolerance combination difference between the two 

arresters. Using this simplified model, we then computed 

the current., powers, and energy depositions in a cascade 

consisting of two #mm varistors for the arresters, and 

a 20-mm varistor for the suppressor, both rated 150 V. 

We postulated a tolerance of + 10% for the line arrester 

and a tolerance of -10% for the neutral arrester. For the 

current imbalance, we postulated respectively 3 kA and 

1 kA for the case of an 8120-ps impinging surge, and 

respectively 200 A and 100 A for a 10/1000-ps surge. 

Figure 12 and Figure 13 show respectively the current 

distributions among the three devices for these two 

impinging surge waveforms. Even with the wide range 

of postulated differences between the arresters, the 

current in the suppressor is negligible. 

Figure 12 

Division of the current among attesters (neutral, I,), 

!!&, i2! em& =g=prese fe 6 1e;O-V r-~dg, 

1 O-m separation, 1 -kA13-kA, 8120-m surge. 

and tolerances of + 10% and -10% on the anesters 

EL....-- ? r aywr nu 

Division of the current among arresters (neutral, I,). 

(line, 12) and suppressor (I3) for a 150-V cascade. 

10-m separation, 1 00-AR00-A, 1 011 000-ps surge. 

and tolerances of + 10% and -1 0% on the arresters 

intuitive anaiysis of highiy noniinear varistor circu

lead to severe errors. However, in this case, the re

the accurate numerical computations can be readily 

stood by recognizing that the difference in voltages at 

N and L is only 20% of the arrester clamping voltag

little to cause a significant current in the suppressor

Thus, a marked difference in the cascade be

occurs, depending upon the neutral earthing pradice 

-. ...lf&. --A at- 11-: ---.I-*-> -__-_-_ uuucy am ruc; w~~npulluwg pusruzueu sr;c:na

coupling the impinging surge. It is important to no

we have presented only two possible configurations 

the many that may be encountered for different cou

Therefore, correct application of surge-protective d

will be achieved only through a good understanding 

context - the grounding practices - of a particular 

cation. Such an understanding will require coordina

the qpEca+;o~ infn_rm_.t;~n &ha A~velnnd --. ;n

-a-r- ... 

Technical Committees or SubcomIlljttees of the Intern

Electrotechnical Commission (IEC), specifically 

(Tnsulation Coordination), SC37A (Low-Voltage 

Protective Devices), 64 @stallation Wiring), SC77B 

Frequency Disturbances), and 8 1 (Lightning Protect

SERVICE ENTRANCE OPTION

Among electric utilities, different philosophi

different standards are encountered on what is dee

be an acceptable temporary overvoltage level. 

instance, in the U.S., ANSI Std C84.1-1989 only 

moderate allowance for temporary overvoltages 

for 'Range B') but acknowledges the possibil

urpater nvewnltaaw QC~, wh& PA^ "

=--I-- ------- v-- 

corrective action shall be taken." The French u

considers that temporary (over 5 seconds) overvolt

1.5 times the nominal system voltage must be acce

a realistic, unavoidable level in their distribution sy

Some utilities may even wish to have a service en

arrester survive the condition of a loose neutral c

tion in a three-wire, neutral bonded to center-tap s

VXAPI~ CIII-.CII+~~- nn An l;nhdrr_lnndarl &An m- 

WLlULU VVGLVUALUgW VLl LUG LlgUUJ-AU4uGU SAUG baLL 

values up to almost twice the nominal system volt

Tbe occurrence of a temporary (seconds) overv

of 1.5 per-unit, or more, is likely to cause massive 

of consumer-type equipment in a residence, raisi

issue of liability of the utility for this failure, in v

the European trends in legislating that 'electricit

product' and that suppliers thereof are liable in th

of a defective product. 

* Communication by J.P. Mcycr at UTE Worksrhop on Surge A

Paris, March 20, 19Y2. 
An effective solution to this problem might be to 

design the service entrance arrester in such a manner that 

its relatively low maximum continuous operating voltage 

(made necessary by the millions of low-rated suppressors) 

wiii cause it to faii - in an acceptahie siton-circuu mode ..A *l.m...-.a.-. -..-&,..A 

-U UGLGU~ ~NLGLL. the qiiipiiieii -iiilt&k the midence. Service would be interrupted and a replacement 

of the ~gmh~t, expedae ave-ger w~idd he rqu~&, 

but the consequential liability of massive appliance 

failures would be avoided. This option seems to merit 

careful examination by the electric utilities, the arrester 

manufacturers, and the standards- or code-writing bodies. 

THE DILEMMA OF SPD VOLTAGE RATINGS 

- 

me foregoing resuits, acided to those presented in the 

many papers cited in the bibliography, forebode quite a 

challenging task of coordinating a cascade downstream of 

the service entrance. This challenge is made even more 

difficult by including the concerns about the 'Low-Side 

Surges' that have led to the recommendation of serviceentrance arresters with ac rms ratings higher than the 

classic 175 V (Dugan & Smith, 1986; Dugan, Kershaw 

& Smith, 1989; Marz & Mendis, 1992). 

Caught between the inescapable, too-late-to-bechanged situation of the 130-V varistors embedded in 

appliances and the recommendation of 175 V or more for 

arresters at the service entrance, the coordination schemes 

proposed by different authors appear elusive: equal 

voltages (Huse, MartzlofQ, lower voltage for the entrance 

(Hasse et al., Standler, Hostfet et al.), or slightly higher 

arrester voltage (Stringfellow). Perhaps, the 1970svintage protection schemes, with a gap-type arrester 

(Martzloff, 1980), rekindled as a result of the new 

coordination issues (Hasse et al., 1989), might be another 

solution. From the diverse interests and expertise of the 

five IEC committees mentioned above, a solution might 

emerge, although it is not obvious at this time. 

CONCLUSIONS 

1. The reality of having many millions of 130-V rated 

varistors installed on 120-V systems, and 250-V 

rated varistors installed on 230-V systems makes the 

ideal scenario of a well-coordinated cascade difficult 

or perhaps unattainable in the near future. 

2. As a compromise, a cascade with equal voltage 

rating for the arreger qygasnr can offer 

successful coordination, if the impinging surges are 

presumed to be relatively short. 

3. The coordination of a simple cascade of an 

and a suppressor of equal voltage ratin

connected line-to-neutral, is slightly improve

larger cross-section of the arrester. Howe

unfavorabie combination of tolerances for 

devices mi wipe out the improvement. 

4. The neutral grounding practice of the utilit

profound effect on the cascade behavior, an

be thoroughly understood for successful app

of cascaded surge protection. Clearly, ad

studies are required in this area. 

5. The waveform of the impinging surge has 

large effect on the outcome. If more da

available on the frequency of occurrence o

surges', some of the uncertainty surround

success of a cascade would be lifted. 

6. The idea of an expendable, one-shot arreste

service entrance could offer a solution out 

dilemma and should be further investigated. 

Jih-Sheng (Jason) La; is a native of Taiwan. He rece

MS. and Ph.D. in electrical engineering from the Univ

Tennessee, Knoxville, in 1985 and 1989, respectivel

1980 to 1983, he was the Electrical Engineering Dep

Chairman of Ming-Chi Institute of Technology, Taipei, 

where he initiated a power electronic program and re

grant from the school and the National Science Co

study abroad. 

In 1989, he joined the EPRI Power Uectronics App

Center, where he is currently the Power Electronics M

His main research interests are power electronics m

andsimulation, circuit design, andmicrocomputer appl

Dr. Lai has 2 patents in high frequency power convers

adjustable speed drives and more than 25 articles pub

the fields of control systems, power systems, and 

electronics. In the surge protection area, he de

varistor models and simulated cascaded surge pr

circuits to understand more about fundamental conc

Franqois 0. MartJoff is a native of France. After 

graduate studies there, he obtained an M3, E.E. at 

- Iech in 1952 and, twenty years later. an M.S., I.A. 

College. After 32 years in the private sector (Souther

Eguipment, 1953- 7956, and GE, 1956- 1985), he joi

National Bureau of Standards, now National lnst

Standards and Technology. His early professional ex

included the design of high-voltage fuses and high

bushings. He changed to semiconductor technology

high-vo/tage experience led him to the study of tra

which he has steadily pursued for the last 30 years. 

As an IEEE Fellow, he has contributed a number o

anti ieu the development of several standards o

characterization and surge testing. He has been gra

patents, mostly on surge protection. In the IEC, he is 

as Convenor of two working groups and chairs Subco

77B (High-frequency Disturbances) of TC77 on 

magnetic Compatibility (EMC). 
APPENDIX - BIBLIOGRAPHY * 

ANSIAEEE 052.41-1991 - Recorrrmended Practice on Surge 

Voltages in Low-Voltage AC Power Circuits. 

ANSI C84.1-1989 - Amen'can National Stcurdard for electnic 

Power Systems and Equipment - Voltage Ratings (60 Hertz). 

Cmur.h, R,F. and Mart710ffi FD. - Lightning P-mtection of 

Residential AC Wiring. Declassified Memo Report MOR-78- 

095, GE Company, 1978. (Available from FD Martzloff) 

Davidson, R. - Suppression Voltage ratings on UL Listed 

Transient Voltage Suppressors. Proceedings, Forum on Surge 

Protedion Application, NISIZR-4657, August 1991, pp 89-92. 

Dugan, R.C. and Smith, S.D. - Low-Voltageside -tSurge Phenomena in Single-Phase Distribution Transformer 

Systems. Prepnepnnt T&D 553-2, IEEE TdiD Confmence, 1986. 

Dugan, R.C., Kershaw, S.S., and Smith, S.D. - Protecting 

Distribution Transformers from Low-Side Current Surges. 

Preprint ID 401-1 PWW, LEEE T&D Conference, 1989. 

Dugan, R. C. - Conduction of Lightning Stroke Currents From 

the Utility System to Load Devices. Conference Proceedings, 

Power Quality '89, Intertech Communications Pub., Ventura 

CA. 

Dugan, R.C., Goedde, G., and Henry, C. - Conduction of 

Lightning Stroke Currents From the Utility System to Load 

Devices. Conference Proadings, Power Quality For End-Use 

Applications, Electric Power Research Institute, Paio Alto, 

March 1990. 

Dugan, KC. - Low-Side Surges: Answers to Common 

Questions. Cooper Power System BuUetin SE9001, April 

1992. 

Hasse, P., Wiesiger, J., and Zischank, W. - Isolationskoordination in Niederspannungsanlagen auch bei 

Blitzehchlagen. Elemotecia. Zeitschn'ft, Jan 1989, pp 64-66. cia -, Engiish iransiation avaiiabie fiom FE Xdv@ 

Hostfet, O.T. et al. - Coordiion of surge protective devices 

in power supply systems: Needs for secondary protection. 

Proceedings, International Conference on Lightning Protedion, 

Berlin, September 1992. 

Huse, 3.P. - Contributions to the revision of Doc 28A(Sec)47, 

Internal document, IEC/SC28A WGO1, 1988. 

IEC 28A(USAfLas Vegas)09 - (Draft) Explcuration for overvoltage categories. December 1984, Amended August 1987. 

IEC 37A/WG3(Convenor/Roma)l - Draft Application Guide, 

January 1992. 

IEC 64/WG3 138A - Explanation of interfaces for overvoltage 

categories. Supplement to Appendix B of Report 664,1990. 

IEC 77(CO) 1 18 Chsi@ation ofElemornugnetic Environments 

Lai, J.S. and Martzloff, F.D. - Coordinating Cascaded Surge 

Protective Devices. Proceedings, IEEE/L4S Annud Meeting, 

October 1991. 

Lai, J.S. - Performance Criteria for Cascading Surge-Pr

Devices. Proceedings, Open Fonun on Surge Pr

Application, MSTIR-4654, August 1991, pp 147-160. 

Lat, M.V. - Determining Temporary Overvoltage Le

Application of Metal-Oxide Surge Arresters on Multig

-.2.. . . - .. m-mY.r uismouuon aysrems. LCCC r ransaaionr r WAU-J, 

1990, pp 936946. 

ar--c-i,cT r n ,,a P -,.- I. v E n-..-a:--~..- 

AV'LQILYV117 I..-. 41lU L1VUbU7 n.E. - -1WVII 

protection contre les Surtensiom dans les r&eaux basse 

dsidentiels. Proceedings, 1978ZEEE Ganadian Confer

Communications and Power, pp 451454. (In French; 

translation available from FD Martzloff) 

Maxtzloff, F.D. - Coordination of Surge Protec

Low-Voltage AC Power Circuits. IEEE Transactions P

Jan"ry/February 1980, pp 129-133. 

Mzdt off, F.D. =& My, T.F. - .Cpl&&g V=;_w C

Voltage: Lower is not Better! Proceedings, 1989 EMC 

Symposium, pp 137-142. 

Martzloff, F.D. - Coupling, Propagation, and Side Ef

Surges in an Industrial Building Wiring System. 

Transactions L4-26, March/April 1990, pp. 193-203. 

Martzloff, F.D. and Lai, J.S. - Cascading Surge-Pr

Devices: Coordination versus the IEC 664 St

Proceedings, PQA 91 Con_ference, pp 191-198. 

Martzloff, F.D. - On the Propagation of Old and New 

Proceedings, @en Forum on Surge Protection App

NISllR-4654, August 1991, pp 19-28. 

Man, M.B. and Mendis, S.R. - Protecting Load Devic

the Effects of Low-Side Surges. Proceedings, IEE

Conference, May 1992. 

Roulet, J.P. - La coordination de I'isolement et le mc

'categorie de surteasion' en base tension. Prodng

Workshop on Surge Arresters, Paris, March 20, 1

French). 

Scuka, V. - Application of modern surge suppressors 

voltage power installation nehoorkr. Institute for High 

a_-&, LTpPdp LT~ym@, ~~~~:19g6. 

Skuka, V. - EM1 Control in Low-Voltage Power Insta

PrnruuAinoc .---R-".-e.., ---. TOR7 FMC -.--- 71irirh ~,~riirm, pp 639-

Standler, R.B. - Coordination of Surge Arreste

Suppressors for Use on Low-Voltage Mains. Proce

199l Ziiricfi EMC Symposium, pp 5 17-524. 

Stringfellow, M.F. and Stonely, B.T. - Coordination o

Suppressors in Low-Voltage AC Power Circuits. Proce

Fonun on Surge Protection Application, MS12R-4657

1991, pp 133-138. 

* Zhe authors and the concerned IEC Working Groups wouki welcome contribruions of additions to this bibliography. 

-8- 
COORDINATING

CASCADED

SURGEPROTECTION

DEVICES:

HIGH-LOW

VERSUS

LOW-HIGH
Reprinted, with permission, from IEEE Transactions on Industry Applications IA-29, July/August 1993 

First presented as ICPSD 91-28 at the IEEE-IAS Annual Meeting, Dearborn, 1991

Significance: 

Part 8 – Coordination of cascaded SPDs 

For a “cascade” of two MOV-based SPDs, the combined numerical modeling and the laboratory 

measurements cross-validate to provide information on the relationship of impinging waveform and 

amplitude, distance between the two SPDs, and relative values of the SPD limiting voltage. 

Results show that separate selection of the service entrance SPD and point-of-use SPD can produce an 

ineffective coordination, with the point-of-use SPD “protecting” the service entrance SPD and in so doing

take on the dissipation of a disproportionate part of the impinging surge energy. 

This situation make the case for giving careful attention to the selection of device parameters, such as 

providing the two devices from an authoritative source from which a well-engineered approach should be 

expected. 

Filename: Coordination 1993 
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 29, NO. 4, JULYIAUGUST 1993 

Coordinating Cascaded Surge Protection 

u 

Jih-Sheng Lai and Fran~ois 

Devices: Hinh-Low versus Low-High 

D. Martzloff, Fellow, IEEE 

Abstract- Cascading surge protection devices located at the 

service entrance of a building and near the sensitive equipment 

is intended to ensure that each device shares the surge stress in 

an optimum manner to achieve reliable protection of equipment 

against surges impinging from the utility supply. However, depending on the relative clamping voltages of the two devices, their 

separation distance, and the waveform of the impinging surges, 

the coordination may or may not be effective. The paper provides computations with experimental verification of the energy 

deposited in the devices for a matrix of combinations of these 

three parameters. Results show coordination to be effective for 

some combinations and ineffective for some others, which is a 

finding that should reconcile contradictory conclusions reported 

by different authors making different assumptions. From these 

results, improved coordination can be developed by application 

standards writers and system designers. 

R ECENT PROGRESS in the availability of surgeprotective devices, combined with increased awareness 

of the need to protect sensitive equipment against surge 

voltages, has prompted the application of a multistep cascade 

protection scheme. In the multistep cascade scheme, a highenergy surge protective device would be installed at the 

service entrance of a building for the purpose of diverting the 

major part of the surge energy. Then, surge-protective devices 

with lower energy-handling capability and lower clamping 

voltage than that of the service entrance would be installed 

downstream and complete the job of protecting sensitive 

equipment at the point of entry of the line cord. To make the 

distinction between these two devices, we will call the service 

entrance "arrester" and the downstream device "suppressor," 

somewhat in keeping with U.S. usage of the transient voltage 

surge suppressor (TVSS) for devices used on the load side 

of the mains disconnect. Such a scheme is described as 

"coordinated" if, indeed, the device with high-energy handling 

capability receives the largest part of the total energy involved 

in the surge event. 

Paper ICPSD 91 -28, approved by the Power Systems Protection Committee 

of the IEEE Industry Applications Society for presentation at the 1991 Industry 

Applications Society Annual Meeting, Dearborn, MI, September 28-October 

4. This work was supported by the Electric Power Research Institute, Power 

Electronics and Control Program, Customer Systems Division. Contributions 

from U.S. Government personnel are not protected by U. S. Copyright. 

Manuscript released for publication September 11, 1992. 

J. S. Lai was with the Power Electronics Applications Center, Knoxville, 

TN 37932. He is now with the Engineering Technology Division, Oak Ridge 

National Laboratory, Oak Ridge, TN 37831-7280. 

F. D. Martzloff is with the National Institute of Standards and Technology, 

Gaithersburg, MD 20899. 

IEEE Log Number 9210072. 

This scenario was based on the technology of secondary 

surge arresters prevailing in the 1970's and early 1980's 

as well as on the consensus concerning the waveform and 

current levels of representative lightning surges impinging 

on a building service entrance. This consensus has gradually evolved toward recognition that the surge environment 

may include waveforms of longer duration than the classical 

8/20 ps current surge. ANSVIEEE C62.41-1991 [I] provides 

a description of the surge environment. With the emergence 

of new types of arresters for service entrance duty and the 

recognition of waveforms with greater duration than the classic 

8/20 ps impulse, a new situation arises that may invalidate the 

expectations of the cascade coordination scenario. 

Service entrance arresters were generally based on the 

combination of a gap with a nonlinear varistor element, which 

was the classic surge arrester design before the advent of 

metal-oxide varistors that made gapless arresters possible. 

With a gap-plus-varistor element, the service entrance arrester 

could easily be designed for a 175-V maximum continuous 

operating voltage (MCOV) in a 120-V (rms) system. The 

downstream suppressors were selected with a low level, driven 

by the perception that sensitive equipment requires a low 

protective level [2]. The scheme can work if there is a series 

impedance (mostly inductance) between the arrester and the 

suppressor because the inductive drop in the series impedance, 

added to the clamping voltage of the suppressor, becomes high 

enough to spark over the arrester gap. Thereafter, the lower 

discharge voltage of the arrester (made possible by the gap) 

ensures that the major part of the surge energy is diverted by 

the arrester, relieving the suppressor from heavy duty [3]. 

Now, if the arrester is of gapless type, its MCOV will 

determine its clamping level. Some utilities wish to ensure 

survival of the arrester under the condition of a lost neutral, 

that is, twice the normal voltage for a single-phase, threewire service connection. The "high-low" combination has been 

proposed, where the arrester clamping voltage is higher than 

that of the suppressor [4]. During the ascending portion of 

a relatively steep surge such as the 8120 ps, the inductive 

drop may still be sufficient to develop enough voltage across 

the terminals of the arrester and force it to absorb much 

of the impinging energy. However, during the tail of the 

surge, the situation is reversed; the inductive drop is now 

negative, and thus, the suppressor with lower voltage (not 

the arrester) will divert the current. For the new waveforms 

proposed in C62.41-1991 [I], this situation occurs for the 

1011000 ps where the tail contains most of the energy, 

and the relief provided by the arrester may not last past 

0093-9994/93$03.00 0 1993 IEEE 
LA1 AND MARTZLOFF: COORDINATING CASCADED SURGE PROTECTION DEVICES 68 1 

TABLE I 

CURVE FITTING RESULTS FOR CIRCUIT MODELING OF THREE MOV'S 

MOV number I, tr X C Ib(v) 

V130LA20A 40x10-'' 30 0051 8x10-" 320 

V150LA20A 3 9 x 10-XY 35 0.053 4 x 370 

V250LA40A 5 7 x 10-1'" 40 004 4 x lop6 570 

the front part of the surge. For the low-frequency (5 kHz 

or less) capacitor-switching ring waves, the inductive drop 

will be much smaller than that occurring with the 8-,us 

rise time so that the additional voltage may be negligible, 

leaving the suppressor in charge from the beginning of the 

event. An alternate means has been proposed (Low-High) 

where the arrester clamping voltage is lower than that of the 

suppressor [5], [6]. Thus, a disagreement has emerged among 

the recommendations for coordinated cascade schemes: the 

1970-1980 perception and [4], suggesting a "High-Low" and 

the new "Low-High" suggestion of [5] and [6]. 

This paper reports the results of modeling the situation 

created by the emergence of gapless arresters and longer 

waveforms with the necessary experimental validation. These 

results cover a range of parameters to define the limits of a 

valid cascade coordination and serve as input to the surge protective device application guides now under development by 

providing a reconciliation of the apparent disagreement, which 

is actually rooted in different premises on the coordination 

parameters. 

The current-voltage (I-V) characteristic of a metal oxide 

varistor (MOV) has long been represented by an exponential 

equation, i.e., I = kV" [7]. This equation is only applicable in 

a certain voltage (current) range in which the I-V characteristic 

presents a linear relationship in a log-log plot. When the 

voltage exceeds this "linear region," the current increment rate 

starts dropping. A modified I-V characteristic is proposed here 

as expressed in (1). 

The parameters in (1) can be obtained from a minimum-errornorm curve fitting technique [8] using a manufacturer's data 

book [7] or experimental results. The parameters k and a can 

be obtained from fitting the data in the linear log-log region. 

The exponential term is added to cover the voltages that are 

higher than a threshold voltage V, and can be obtained from 

fitting the I-V characteristics in the higher current (voltage) 

region. Using (I), the MOV circuit model can be simply 

represented by a voltage-dependent current source. 

Model parameters in (1) can be obtained from the manufacturer's data book and verified by experiments. The parameter is 

typically a function of the MOV voltage rating. The threshold 

voltage VO and coefficients X and C are functions of the voltage 

rating and the size. Table I lists curve fitting results for the 

Peak Current (A) 

Fig. 1. MOV characteristics obtained from modeling results 

TABLE I1 

PARAMETERS FORNOMINAL I-V CHARACTERISTICS OF THREE MOV'S 

MOV number I; a X c r ;(v) 

V130LA20A 9.4 x I()-" 27 0.046 0.8 x lop6 285 

V150LA20A 4.8 x lopT9 31.5 0.053 1.6 x 340 

V250LA40A 1.7 x lopg7 36 0.044 1.6 x lop" 520 

equivalent circuit parameters of three MOV's for units of 

voltage and current in volts and amperes. 

The MOV number1 actually reflects the device voltage 

rating and the size. For V130LA20A, the continuous operating 

voltage rating is 130 V(rms). The other two devices are 150 

and 250 V(rms), respectively. All three devices have a 20-mm 

diameter. Fig. 1 shows fitted curves for the three devices. 

In Fig. 1, the marked dots were the data directly obtained 

from the manufacturer's data book, whereas the three solid 

lines were calculated from (1) using the parameters listed in 

Table I. 

It should be noted that each individual MOV may have 

slightly different I-V characteristics even with the same model 

number. In Fig. 1, the data show the maximum clamping 

voltage levels, which are 10% higher than the nominal voltage 

level. A typical off-the-shelf device has a tolerance within 

&lo% of the nominal voltage level, which means a lowestlevel device could have an I-V characteristic that is 20% lower 

than the data book characteristics. In fact, the two closely 

rated cascading devices (130 and 150 V) could, in some 

extreme cases, become inverted in the sequence ("Low-High" 

becoming in reality "High-Low") as 130 x 1.1 = 143 and 

150 x 0.9 = 135. Furthermore, the results show that for the 

250-150 combination, the difference is so large that a low 

250 (225 V) combined with a high 150 (165 V) would not 

make an appreciable difference in energy sharing. Thus, the 

simulation computations were performed for all three devices 

at their nominal values. From the maximum voltage tolerance 

parameters listed in Table I, the parameters for the nominal 

(zero tolerance) I-V characteristics were derived, as listed in 

Table 11. 

'Certain commercial products are identified in this paper in order to 

adequately specify the experimental procedure. Such identification does not 

imply recommendation or endorsement by the Power Electronics Applications 

Center or the National Institute of Standards and Technology, nor does it imply 

that the products are necessarily the best for the purpose. 
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 29. NO. 4. JULYIAUCUST 1993 

#I2 wire 

Arrester 

Surge 

Generator 

Fig. 2. Two-stage cascade surge protection system. 

TABLE I11 

NINE POSSIBLE CASCADE COMBINATIONS FOR THREL DEVICES 

Arrester Suppressor 

250 V 

250 V 150 V 

111. SIMULATION OF CASCADED SURGE PROTECTION 

DEVICES IN A LOW-VOLTAGE SYSTEM 

In a two-stage cascade surge protection system, the arrester 

is placed near the surge source (the service entrance for 

premises wiring), and the suppressor is placed near the load. 

Fig. 2 shows a typical two-stage cascade surge protection 

system. The arrester and the varistor are separated by a 

distance d, which depends on the specific installation. In 

the following simulation study, four different d values are 

considered. They are 5, 10, 20. and 40 m. The #12 wire 

is a typical size for the premises wiring and is used for 

the following simulation and experiment study. Based on an 

impedance-meter measurement, the resistance of #12 wire 

is 0.00104 R/m, and the inductance is 1 pH/m (per two 

parallel wires). For high-frequency waves (the 1.2150 - 8120~s 

Combination Wave and the 0.51~~ - 100 kHz Ring Wave), 

the inductive drop is the more dominant [9]. The complete 

simulation consists of a surge source, two voltage-dependent 

current sources, and a line impedance between the two current 

sources [ 101. 

For the three selected device voltage levels, there is a total 

of nine possible cascade combinations as shown in Table 

111. Three standard waves from [l] were chosen to cover 

different frequency responses. These are 1.2150 - 8120~s 

Combination Wave, 0.5 - 100 kHz Ring Wave, and 1011000ps 

impulse wave. For the sake of brevity, these three waveforms 

will be called "Combo Wave," "Ring Wave," and "Long 

Wave." For four distances, three voltage waves, and nine 

cascade combinations, a total of 108 cases were studied in the 

simulation: about 200 hours of machine time on a 25-MHz 

personal computer. 

A. Simulation Results with the Combination Wave 

Because of the back filter effect, a waveform generator 

might not couple a true standard wave to the test circuit. Fig. 

Fig. 3. Standard 8/20 ps short-circuit wave and a possible negative swing 

caused by the filtering circuit. 

Fig. 4. Simulated Combo Wave current responses for the 250-130V cascaded devices that are 10-m apart. 

3 shows an oscillation of the standard 8120~s current wave. 

Curve A is the standard 8120ps current, and curve B is the 

actual coupled wave with a small negative swing. For the 

standard 8/20ps wave, the current is always positive, and the 

clamping voltage is always positive. When applying curve B 

as the surge source, the negative current portion will cause 

a negative clamping voltage. This has been observed in the 

experiments. In order to reflect the experimental results, the 

following simulation will use curve B as the combo wave 

source. 

Consider a 250-130 V cascade of two devices that are 10 

m apart. The simulation results of the currents flowing in 

the two devices are shown in Fig. 4, where It is the total 

current injected into the cascade by the surge source of the 

model, II is the arrester current, and I2 is the suppressor 

current. Fig. 5 shows device clamping voltages with Vl and V2 

representing arrester and suppressor voltage, respectively. Fig. 

6 shows instantaneous powers with PI and fi representing 

arrester and suppressor power, respectively. By integrating 

the instantaneous power, the energy deposition values in the 

arrester and the suppressor were calculated as 29.7 and 8.6 J, 

respectively. 

Before proceeding with further simulations, the simulation 

results were verified by an experiment. With the experimental 

setup of Fig. 2 and 250 and 130 V rated devices in cascade, the 

experimental results for the arrester and suppressor are shown 

in Fig. 7. Because the surge generator generates nonstandard 

waveforms, the waveforms obtained from the experiment are 

not exactly the same as the simulated waveforms. However, 

the power distribution between the two devices shows good 

agreement between simulation and experiment. For the same 
LA1 AND MARTZLOFF: COORDINATING CASCADED SURGE PROTECTION DEVICES 

Fig. 5. Simulated Combo Wave voltage responses for the 250-130 V cascaded devices that are 10-m apart. 

Fig. 6. Simulated Combo Wave power responses for the 250-130V cascaded 

devices that are 10-m apart. 

250-130, 10-m cascaded case but slightly higher peak surge 

current (3.3 kA instead of 3 kA in simulation), the experimental result shows 33.8 and 11.1 J energy depositions in 

the arrester and the suppressor, respectively. Prorating the 

simulation results from Fig. 6 to 3.3 kA would yield 32.7 

and 9.5 J, respectively, which is a reasonable agreement. 

Table IV lists Combo Wave simulation results of the energy 

deposition in the arrester (A) and suppressor (S) for all the 

combinations of different High-Low and Low-High cascade 

conditions. For the High-Low condition, the energy deposition 

in the suppressor increases when the distance decreases. This 

result explains how the High-Low configuration can achieve a 

good coordination under the Combo Wave, provided that there 

is sufficient distance between the two devices, as stated in [3]. 

Consider the High-Low configuration with a 250-V device 

as the arrester. When the distance between two devices is reduced, the energy deposition tends to increase in the suppressor 

and decrease in the arrester. This decrease occurs because 

the line inductance does not provide enough voltage drop 

(L dildt), and the low clamping voltage of the suppressor 

reduces the voltage across the arrester and thus reduces the 

energy deposition level. The total energy deposition in the 

two devices also varies with the distance for the HighLow configuration. In Table IV, the total energy deposition 

for the 250-250 combination is near constant at 103 J for 

different distances. However, for the 250-150 and 250-130 

combinations, the total energy deposition decreases when the 

distance is reduced because the suppressor tends to lower the 

voltage across the arrester. 

For Low-High configurations such as the 150-250 and 

130-250 cases, the high-voltage suppressor receives almost 

zero energy. The use of the suppressor is near redundant 

TABLE IV 

ENERGY DEPOSITION IN THE CASCADED DEVICES 

WITH A 3-kA COMBO WAVE AS THE SURGE SOURCE 

Clamping Distance separating devices and energy deposited in each 

voltage of device (J) 

device (V) 5 m 10 m 20 m 40 m 

ASASASASAS 

250 75.9 27.3 83.5 19.9 89.5 14.4 91.7 9.69 

in this case, except for its application to mitigate internally 

generated surges. With closely rated devices (130-150), the 

150-V voltage suppressor also receives much less energy than 

the 130-V arrester. 

B. Simulation Results with the 0.5 ,us-100 kHz Ring Wave 

The energy deposition in the surge protection devices under 

the Ring Wave surge is considerably less than that of the 

Combo Wave because of lower current. However, the highfrequency Ring Wave shows similar characteristics to the 

Combo Wave under the High-Low cascade condition; a voltage 

drop between the two devices can be established by the line 

inductance, provided that there is sufficient distance between 

the two devices. Figs. 8 and 9 show simulation results of 

current and voltage for the cascaded arrester and suppressor 

under the High-Low condition. Il and Vl represent the 250- 

V arrester current and voltage, whereas 12 and V2 represent 

the 130-V suppressor current and voltage, respectively, for a 

400-A peak surge current. 

Fig. 10 shows the instantaneous power dissipated in the 

two cascaded devices. PI and P2 represent the 250-V arrester 

power and 130-V suppressor power, respectively. 

Table V lists the simulated energy deposition in the cascaded 

devices for different High-Low and Low-High combinations. 

The energy is the integration of the instantaneous power over 

the total 20-ps simulation period. Unlike the Combo Wave, 

the Ring Wave tail still contains a small amount of power, 

and the total amount of the energy deposition is affected by the 

integration interval. From Fig. 10, it is apparent that the power 

contribution to the total (past 20 ps) is becoming negligible. 

Similar to the Combo Wave, the High-Low configuration 

shows good coordination as the high-voltage arrester absorbs 

higher energy under the high-frequency Ring Wave surge, 

and the Low-High configuration shows almost zero energy 

deposition in the high-voltage suppressors. 

C. Simulation Results with the 10/1000 ,us Long Wave 

Compared with the Combo Wave, the Long Wave has a 

slower and longer drooping tail that contains most of the surge 

energy. During the long tail period, the inductive voltage drop 

between the arrester and the suppressor is low due to low 

Ldildt, and the voltage across the arrester is reduced by the 
683 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 29, NO. 4, JULYIAUGUST 1993 

I,+[,. 1000 Nd~v 

I,: 1000 Nd~v 

Fig. 7. Experimental results for the 250-130 V cascade with devices that are 10-m apart, with the Combination Wave: (a) Arrester; (b) suppresor. 

TABLE V 

ENERGY DEPOSITIOK IN THE CASCADED DLVICES WITH 

A $00-A PEAK RING WAVE AS THE SURGE SOURCE 

Clamping Distance separating devices and energy deposited in each 

voltage of device (J) 

device (V) 5 m 10 m 20 m 40 m 

ASASASASAS 

250 1.287 0.398 1.405 0.291 1.512 0.158 1.593 0.114 

250 150 0.996 0.625 1.301 0.317 1.536 0.127 1.613 0.094 

130 0.938 0.501 1.213 0.312 1.425 0.183 1.624 0.083 

250 1.21 0.002 1.21 0.003 1.21 0.003 1.21 0.004 

150 150 1.05 0.15 1.11 0.097 1.15 0.059 1.17 0.035 

suppressor even with long distance between the two devices. 

This makes the High-Low configuration not coordinated as the 

high-voltage arrester will not absorb any impinging energy, but 

the suppressor does. Figs. 11, 12, and 13 show the simulated 

Long Wave current, voltage, and power, respectively, for 

the arrester and the suppressor under a High-Low (250-130) 

configuration for a 200-A peak surge current. 

The high-voltage arrester clamps the voltage during the 

impulse rising period and draws a small amount of the current 

pulse 11, which is almost invisible in the computer-generated 

plot of Fig. 11. The power absorbed by the arrester PI is also 

a small pulse that appears at the rising period as shown in 

Fig. 13. The low-voltage suppressor absorbs all the impinging 

energy in this High-Low configuration, defeating the intended 

coordination. 

Table VI lists the simulated energy deposition in the cascaded devices for different High-Low and Low-High combinations as well as for different distances. 

It can be seen from Table VI that the low-voltage device 

always absorbs higher energy than the high-voltage device 

because the voltage across the high-voltage device is clamped 

to the same level as that of the low-voltage device, and the 

energy is diverted to the low-energy device. Unlike the Combo 

Wave and the high-frequency Ring Wave, the coordination for 

Fig. 8. Simulated Ring Wave current responses for the 250-130 V cascaded 

devices that are 10-m apart. 

Fig. 9. Simulated Ring Wave voltage responses for the 250-130 V cascaded 

devices that are 10-m apart. 

the slow Long Wave can only be achieved by Low-High or 

equally rated devices (250-250, 150- 150, and 130- 130). Note 

that with two devices of equal nominal value, it is possible 

that the relative tolerance might, in fact, produce a HighLow situation, which would not achieve good coordination; 

for instance, a 150- 130 combination resulting from tolerance 

shifts imposes a 70-J duty to the suppressor in the case of 

5-m separation. 

IV. EXPERIMENTAL RESULTS 

In order to verify the validity of the simulation, a series 

of experiments has been conducted using the three waves for 

different High-Low and Low-High combinations, especially 
LA1 AND MARTZLOFF. COORDINATING CASCADED SURGE PROTECTION DEVICES 685 

Fig. 10. Simulated Ring Wave instantaneous power for the 250-130 V 

cascaded devices 10-m that are apart. 

Fig. 11. Simulated Long Wave current responses for the 250-130 V cascaded 

devices that are 10-m apart. 

Fig. 12. Simulated Long Wave voltage responses for the 256130 V cascaded devices that are 10-m apart. 

for the Long Wave, which has not been used for cascaded 

coordination studies in the literature. Table VII lists experimental results (from Figs. 7, 14, and 15) using the three 

waveforms for 250-130 V cascaded devices that are 10-m 

apart. Note that peak currents do not occur simultaneously. 

A * sign shows that the low-voltage suppressor absorbs 

almost all the energy under the 10/1000 ps Long Wave. The 

experimental results, in general, agree with the simulation 

results, especially for the Combo Wave, which has well 

matched surge sources and a limited surge period (the tail does 

not extend over the integration period). For the Ring Wave 

and the long wave, the total integration period and the surge 

source are not matched between simulation and experiment, 

and thus, the numbers in Table VII have higher deviation 

from the simulation results. However, the proportion between 

the arrester and the suppressor energies agrees well between 

simulation and experiment, which explains that the simulation 

can be effectively used for the coordination analysis. 

Fig. 13. Simulated Long Wave power responses for the 250-130 V cascaded 

devices that are 10-m apart. 

TABLE VI 

ENERGY DEPOSITION I THE CASCADED DEVICES 

wrr~ A 220-A PEAK LONG WAVE SURGE SOURCE 

Clamping Distance separating devices and energy deposited in each 

voltage of device (J) 

device (V) 5 m 10 m 20 m 40 m 

ASASASASAS 

250 73.63 72.76 74.10 72.31 75.06 71.38 76.28 70.13 

250 150 0.031 92.15 0.028 92.03 0.69 91.70 1.77 91.00 

TABLE VII 

EXPERIMENTAL RESULTS USING DIFFERENT WAVEFORMS FOR 

250-130 V CASCADEDEVICES THAT ARE 10-M APART 

Applied Arrester Suppressor 

Wave Vpk (V) Ipk (A) W (J) Vpk (V) I,n (A) fi'(J) 

pzFk 790 2600 33.8 400 1000 11.1 

43plgpk 720 340 0.6 350 100 0.2 

450 6 0.05 320 220 64.4* 

The experimental verification of the Combo Wave for the 

simulation can be seen from Fig. 7. For the Ring Wave and the 

Long Wave, experimental current, voltage, and power waves 

are shown in Figs. 14, 15, and 16, respectively. The Ring Wave 

coupled from the surge generator is distorted and is attenuated 

much faster than the standard Ring Wave. The measurement 

of the coupled Long Wave shows a saturation on the small 

CT (5000 A peak and 65 A rms rated). However, the current 

flowing through the surge protection devices were measured 

by a large CT (20 000 A peak and 325 A rated) and were 

not saturated. 

The experimental Long Wave response for a Low-High 

configuration is shown in Fig. 16, where Il and I2 are 

the currents flowing in the 130-V arrester and the 150-V 

suppressor, respectively. This figure shows an example of good 

coordination by Low-High, where most of the surge energy is 

absorbed by the low-voltage arrester. The arrester voltage Vl 

is almost the same as the suppressor voltage V2 with a slight 

difference at the beginning of the surge. 
lEEE TRANSACTIONS ON INDUSTRY APPLICATIONS. VOL. 29. NO. 1. JULYIAUGUST 1993 

1,+1,: 100 Ndiv 

1,: 100 Ald~v 

I,+/?: 100 Ndiv 

I,: 100 Ndiv 

V,: 400 Vldiv 

P,: 40 kW/div 

Fig. 14. Experimental results for the 250-130 V cascade, with devices that are 10-m apart, with the Ring Wave: (a) Arrester; (b) suppresor. 

(a) (b) 

Fig. 15. Experimental results for the 2.50-130 V cascade, with devices that arc 10-rn apart, with the Long Wave: (a) Arrester; (b) auppresor. 

V. DISCUSSION 

The concept of coordination of surge-protective devices is 

based on the selection of a first device with high energyhandling capability that is to be located at the service entrance 

and is expected to divert most of the surge current at that point. 

The second device, which is installed within the premises, can 

then have a lower energy-handling capability. 

The benefit from this coordinated approach is to allow a 

single device at the service entrance to perform the high-energy 

duty, whereas several smaller devices within the premises 

can perform local suppression. This arrangement avoids the 

flow of large surge currents in the branch circuits of the 

installation, which is a situation known to produce undesirable 

side effects [l 11. 

On the other hand, the situation where millions of small 

suppressors have been installed within equipment, or as plugin devices, exists with only sporadic and anecdotal reports of 

problems. Thus, it is evidently possible to obtain protection 

with suppressors alone, whereas a coordinated scheme would 

provide additional bcnefits and eliminate side effects. 

Some utilities wish to provide a service-entrance arrester 

thta is capable of withstanding the 240-V overvoltage that 

can occur on the 120-V branches when the neutral is lost. 

Fig. 16. Expcrirnental resulrs for the 130-150 V cascade, with devices that 

are 10-m apart, with thc Long Wave. 

This desire will force the coordination scheme into a HighLow situation because of the uncontrolled installation of low 

clamping voltage suppressors by the occupant of the premises. 

The results of the simulation and experimental measurements 
LA1 AND MARTZLOFF: COORDINATING CASCADED SURGE PROTECTION DEVICES 

show that the objective of coordination could still be achieved REFERENCES 

with a 250-130 combination, as long as some distance is 

[I] ANSI/IEEE C62.4 1 - 199 1, IEEE Recommended Practice on Surge Volt- provided between the two devices and as long as Long Waves ages in Low-Voltage ac Power Circuits. 

are not occurring with high peak values. This proviso provides [2] F. D. Martzloff and T. F. Leedy, "Selecting varistor clamping voltage: 

an incentive for obtaining better statistics on the occurrence Lower is not better!" in Proc. 1989 EMC Symp. (Ziirich). ., of L~~~ waves. ANS~/IEEE (-62.41-1991 ~41 [3] F. D. Martzloff, "Coordination of surge protectors in low-voltage ac 

power circuits," IEEE Trans. Power App. Syst., vol. 99, pp. 129-133, considering these Long Waves as an additional and not a Jan./Feb. 1980. 

standard waveform. Thus, the determination of a successful 141 

. . M. F. Stringfellow and B. T. Stonely, "Coordination of surge - suppressors .- 

coordination depends, for the moment, on the perception of in low-voltage ac power circuits," in Proc. Open Forum Surge Protection 

Application, NISTIR 4657, June 1991. what the high-energy waveforms can be for specific [5] R. B. Standler, "Coordination of surge arresters and suppressors for use environments. on low-voltage mains." in Proc. 1991 EMC Svmo. (Ziirich). 

VI. CONCLUSIONS 

Coordination of cascaded devices can be achieved under 

various combinations of parameters, but some combinations will result in having a suppressor with low 

energy-handling capability called on to divert the largest 

part of the surge energy. This uncoordinated situation 

can create adverse side effects when high current surges 

occur. 

Significant parameters in achieving successful coordination involve three factors over which the occupant 

of the premises has no control: the relative clamping 

voltages of the two devices, their separation distance, 

and the prevailing waveforms for impinging surges. This 

uncontrolled situation presents a challenge and obligation for standards-writing groups to address the problem 

and develop consensus on a tradeoff of advantages and 

disadvantages of High-Low versus Low-High. 

Coordinated schemes can be proposed by utilities to 

their customers, including a service entrance arrester 

and one or more plug-in devices to be installed for the 

dedicated protection of sensitive appliances. However, 

even such an engineered, coordinated arrangement could 

be defeated by the addition of a suppressor with a 

very low clamping voltage, which is not an insignificant 

likelihood in view of the present competition for lower 

clamping voltages. 

VII. UPDATE ON COORDINATION EFFORTS 

Since the presentation of the paper in the Fall of 1991, considerable discussion of the coordination issue has taken place 

at the international level involving five technical committees 

of the IEC. As of late 1992, an effort is underway within 

the IEC to develop an application document that will address 

the issues discussed in this paper and present recommendations tailored to the specific neutral-grounding practice of 

the various member countries. Contact the authors for further 

updates on progress concerning the technical aspects of device 

coordination issues as well as updates on the intercommittee 

coordination and liaison. 

ACKNOWLEDGMENT 

The authors wish to thank W. P. Malcolm of EPRI for 

his continued support. Thanks are also due to A. M. Maher 

and R. A. Veira of PEPCO and T. S. Key of PEAC for their 

encouragement in this project. 

... ~ 

[6] IEC 641~~: 138A, ''~x~lanation of interfaces for overvoltage categories," Supplement to Appendix B of Rep. 664, Nov. 1990. 

[7] Transient Voltage Suppression Devices, Harris Corp., 199 1. 

[8] D. G. Luenberger, Linear and Nonlinear Programming. Reading, MA: 

Addison- Wesley, 1984. 

[9] F. D. Martzloff, "On the propagation of old and new surges," in Proc. 

Open Forum Surge Protection Application, NISTIR 4657, June 1991. 

[lo] J. S. Lai, "Performance criteria for cascading surge-protective devices," 

in Proc. Open Forum Surge Protection Application, NISTIR 4657, June 

1991. 

[I 11 F. D. Martzloff, "Coupling, propagation, and side effects of surges in an 

industrial building wiring system," IEEE Trans. Industry Applications, 

vol. 26, no. 2, pp. 193-203, Mar./Apr. 1990. 

Jih-Sheng (Jason) Lai is a native of Taiwan. He 

received the M.S. and Ph.D. degrees in electrical engineering from the University of Tennessee, 

Knoxville, in 1985 and 1989, respectively. 

From 1980 to 1983, he was the Electrical Engineering Department Chairman of Ming-Chi Institute 

of Technology, Taipei, Taiwan, where he initiated 

a power electronic program and received a grant 

from the school and the National Science Council 

to study abroad. In 1989, he joined the EPRI Power 

Electronics Applications Center. He is currently the 

Power Electronics Lead Scientist at thk Engineering Technology Division 

of the Oak Ridge National Laboratory. His main research interests are 

power electronics modeling and simulation, circuit design, and microcomputer 

applications. In the surge protection area, he developed varistor models 

and simulated cascaded surge protection circuits to understand more about 

fundamental concepts. 

Dr. Lai has two patents in high-frequency power conversions for adjustablespeed drives and more than 25 articles published in the fields of control 

systems, power systems, and power electronics. 

Franqois D. Martzloff (F'83) is a native of France. 

After undergraduate studies there, he received the 

M.S.E.E. degree from Georgia Institute of Technology, Atlanta, in 1952 and the M.S.I.A. degree from 

Union College, Schenectady, NY, in 1972. 

After 32 years in the private sector (Southern 

States Equipment from 1953-1956 and General 

Electric form 1956-1985). he joined the National 

Bureau of Standards, which is now the National Institute of Standards and Technology, Gaithersburg, 

MD. His early professional experience included the 

design of high-voltage fuses and bushings. He changed to semiconductor 

technology, but his high-voltage experience led him to the study of transients, 

which he has steadily pursued for the last 30 years. He has contributed a 

number of papers and led the development of several standards on surge 

characterization and surge testing. 

Mr. Martzloff has been granted 13 patents, mostly on surge protection. In 

the IEEE, he serves as Chair of the Working Group on Surge Characterization. 

In the IEC, he is serving as Convenor of two working groups and chairs Subcommittee 77B (High-Frequency Phenomena) of TC77 on Electromagnetic 

Compatibility. 
GAPPED

ARRESTERS

REVISITED:

A SOLUTION

TO

CASCADE

COORDINATION
Reprinted, with permission, from IEEE Transactions PWRD13 No.4, December 1998 

(First presented as PE-114-PWRD-0-12-1997) 

Significance 

Part 8 – Coordination of cascaded SPDs 

The goal of implementing a well-coordinated cascade of SPDs with simple MOVs at both the service entrance o

building and point-of-use (the latter typically by an add-on plug-in SPDs typical of what consumers purchase from 

electronic stores – the so-called “TVSS”) presents a dilemma because the service entrance arresters tend to be 

designed with conservative MCOV ratings (hence relatively high limiting voltages) while the TVSSs tend to be 

designed with the lowest possible limiting voltage. Such relationship in the limiting voltages is the contrary of wh

is necessary to achieve coordination between the rugged service entrance arrester and the limited energy-hand

capability of the TVSS. 

The situation has been created by the decision, early in the introduction of TVSSs and possibly motivated by the 

requirement to show the limiting voltage (with a misguided notion that a lower limiting voltage ensures better 

protection). By now, this de facto presence of millions of low limiting voltage for the TVSS makes it practically 

impossible to achieve coordination if the twp SPDs consist of simple MOVs. 

Ironically, upon introduction of MOVs in the mid-seventies, residential-type service entrance arresters that consi

of a series combination of a gap and a silicon carbide varistor were replaced by simple MOV discs, viewed at th

time as a significant improvement of the protective level provided by a service entrance arrester – hence the 

“revisited” aspect of this paper. 

A solution to this dilemma might be to design the service entrance as a gapped arrester that can relieve the TVS

from the major part of the energy-dissipation stress, while the de facto TVSS can still provide point-of-use surge 

protection for the connected loads. 

This paper was designated “High Interest Paper” by the Power Engineering Society 

Filename: Gapped arresters
1174 IEEE Transactions on Power Delivery, Vol. 13, No. 4, October 1998 

Gapped Arresters Revisited : A Solution to Cascade Coordination 

Arshad Mansoor, Member, IEEE Fran~ois D. Martzloff, Fellow, IEEE Kermit 0. Phipps Member, IEEE 

Power Electronics National Institute of Power Electronics 

Applications Center Standards and Technology * Applications Center 

Knoxville TN Gaithersburg MD Knoxville TN 

Abstract - This> paper provides a brief perspective on how the 

coordination of cascaded surge-protective devices (SPDs) has become an issue. We propose an approach where the 'ancient' technology of 

gapped arresters may well be the answer to the dilemma of the 

incompatibility of a service-entrance SPD having relatively high 

limiting voltage with the proliferation of built-in or plug-in SPDs 

having relatively low limiting voltage inside the buildings. The 

solution involves providing a gapped arrester at the service entrance 

and gapless SPDs inside the building. An example is given of such a 

combination, with experimental verification of the proposed solution 

and computer modeling that allows a parametric evaluation of the 

significant factors in any candidate combination of SPDs. 

I. INTRODUCTION 

A quarter of a century ago, metal-oxide varistors 

("MOVs"), initially developed as electronic components [I], 

121, were introduced to power-system applications and were 

promptly hailed as the revolutionary technology that would 

make possible the elimination of gaps in surge arresters and 

surge-protective devices (SPDs) in general [3]. The conventional arresters at that time combined a gap with a silicon 

carbide (Sic) varistor disc because the I-V characteristic of 

silicon carbide, for the desired protection level under surge 

conditions, resulted in excessive standby current under the 

normal power system conditions. 

For the high-voltage surge arresters, this Sic varistor-gap 

combination had reached great sophistication in the development of gap structures and construction with modular elements. 

For low-voltage applications, one Sic varistor disc and one gap 

were sufficient for the arrester function, but only a few of that 

type were used in residential applications. The gap sparkover 

characteristics made the device adequate enough for insulation 

protection but not effective for the protection of the emerging 

solid-state appliances [4]. Thus, a market was opened for allMOV arresters to replace Sic-based gapped arresters and, as 

the cliche goes, the rest is history. 

" Electricity Division, Electronics and Electrical Engineering Laboratory, 

Technology Administrution, U.S. Department of Commerce. 

Contributions,from the National Institute and Technology are not subject 

to U.S. Copyright. 

PE-114-PWRD-0-12-1997 A paper recommended and approved by the 

IEEE Surge Protective Devices Committee of the IEEE Power 

Engineering Society for publication in the IEEE Transactions on Power 

Delivery. Manuscript submitted June 9, 1997; made available for 

printing December 12, 1997. 

However, this apparently happy state of affairs with the 

new, improved, MOV-based gapless SPDs is not the end of the 

story. Arresters developed with electric utility applications in 

mind were designed by specialists with strong motivation to 

ensure a reliable, long-life and ultimately cost-effective 

application of their products. This philosophy included due 

consideration of the maximum continuous operating voltage 

(MCOV), where the drive for low protection levels was 

tempered by the need to survivc the variations and extremes of 

the power system environment. This criterion was well 

understood by utilities and manufacturers. 

In this paper, we propose to show the opportunity to 

revive - revisit - the approach of a gapped arrester that was 

all but abandoned, as a possible solution to the dilemma of 

coordination between an arrester designed with a prudent and 

conservative MCOV at the service entrance, and the many 

SPDs proliferating inside the building and having a de facto 

low limiting voltage. This paper is not a product announcement 

but is an invitation to both manufacturers and users to recognize 

the opportunity and develop a viable product based on this 

revisited approach. We only suggest that an appropriate 

coordination is possible between an arrester capable of 

withstanding high temporary overvoltages, according to utility 

practice, and the small, de facto SPDs inside the building. We 

leave the actual product design to the ingenuity and skill of SPD 

manufacturers responding to the need of the utilities. 

11. THE RACE FOR LOWEST PROTECTION LEVEL 

Those designs are now found throughout utility systems, 

down to the service entrance of the end-user customers. 

Meanwhile, the designers of appliances, driven by the economic 

pressures of mass production, had selected solid-state components with relatively low surge immunity. This fateful design 

and marketing decision led to the need for adding surgeprotective devices at the equipment level (incorporated at the 

power port of the appliance), or as an interface plug-in device 

separately purchased and installed by the end-user. There, the 

motivation became one of offering the lowest conceivable 

protection level, for instance 330 V for 120-V applications [5]. 

However, some of the implications of this race for the lowest 

protection level were not fully recognized [6]. 

Now, an additional concern is emerging as the idea of the 

so-called "wholehouse surge protection" is gaining popularity. 

In that scheme, a relatively large SPD is installed at the service 

entrance and additional, smaller SPDs are installed inside the 

building to complement the first line of protection provided at 

the service entrance. The service-entrance arrester would be a 

simple (gapless) varistor SPD, based on the conservative 

0885-8977/98/$10.00 O 1997 IEEE 
approach of the utilities (sufficient MCOV, hence medium level 

limiting voltage for the SPD). However the de facto situation 

inside the building is the uncontrolled proliferation of small 

SPDs with low limiting voltage. Note that given the uncoordinated status of cascaded SPDs, it would be pointless to try and 

pin down precisely the qualifiers of 'high', 'medium' and 'low' 

limiting voltage. The point is only to indicate a relative level. 

This situation is uncontrolled because the design and 

surge immunity of appliances has not benefitted from generic 

standards on surge immunity. The result is that the small SPDs 

can in fact 'protect' the service entrance arrester and invite the 

largest part of an impinging surge to pass by the entrance 

arrester - intended to divert the large surges but by-passed - to be dissipated into the small devices - that might not be 

suitable for the large surge. 

At this point of our discussion, we deliberately use the 

vague qualifier "large" to refer to the size and energy-handling 

capability of an SPD and to the stress threat of the impinging 

surge [7]. An additional concern is that inviting the flow of 

large surge currents inside the building has adverse side effects 

from the electromagnetic compatibility (EMC) point of view by 

shifting the potential of signal reference points associated with 

the equipment grounding conductors [8]. 

111. EMERGENCE OF COORDINATION ISSUES 

These emerging issues led to the recognition of "Cascade 

Coordination" as an important objective for the application of 

SPDs. A coordinated cascade is the parallel connection of two 

or more SPDs across the line, one upstream and one or more 

downstream, each with voltage limiting characteristics that 

ensure sharing of the surge energy in a ratio commensurate with 

the energy-handling capability of each SPD. 

The stage was set nearly two decades ago, with the 

publication of IEC Report 664 on insulation coordination [9] 

proposing "Installation Categories" with a descending staircase 

of voltages from the service entrance to the end of the branch 

circuits in a building. That concept was valid at the time, based 

on the availability of conventional arresters using a siliconcarbide varistor in series with a gap. Consequently, equipment 

manufacturers, including manufacturers of SPDs, became 

biased toward a philosophy that advocated higher limiting 

voltage at the service entrance and progressively lower limiting 

voltages inside the building. 

It took some time and several contributions from 

independent researchers to recognize that this downward 

staircase cannot be implemented by a cascade of parallelconnected, varistor-type SPDs, even if separated by some 

distance along the wiring from the service entrance to the end 

of the branch circuits. This reality was first discussed in several 

unpublished committee working papers before a rush of 

published papers brought the realization into the open [lo], 

[ll], [12], [13], [14]. It turns out that SPDs included in 

equipment or added by users have lower lirmting voltages than 

all-varistor SPDs installed at the service entrance and thus 

unintentionally "protect" the service entrance SPD by attracting 

the surge current to the device with the lowest limiting voltage. 

IV. A POSSIBLE SOLUTION: RETURN 

TO A GAPPED ARRESTER 

This gapped arrester will use a varistor with a limiting 

voltage lower than that of the downstream SPDs (in all the 

following text, "varistor" is to be understood as short-hand for 

metal-oxide varistor). The gap in series prevents steady-state 

application of the line voltage which the varistor cannot sustain 

for more than one half-cycle. An impinging surge will cause 

the gap to spark over, inserting the low-limiting varistor ahead 

of the downstream varistors. We have postulated that by 

appropriate selection and design of the gap, the powerfrequency current which will flow in the varistor after the surge 

will be cleared by the gap at the first natural current zero. 

4.1 Criteria for coordination 

The basic principle of coordination for a cascade is that 

the two SPDs - for instance one upstream at the service 

entrance, and one downstream at the end of a branch circuit or 

incorporated in the connected equipment - are decoupled from 

each other by some impedance. With a gapped arrester at the 

service entrance with a varistor with limiting voltage lower than 

that of the downstream SPlDs can serve as the most attractive 

SPDs in the cascade and thus divert the surge current away 

from internal branch circuits after the gap has sparked over. 

The gap can also serve to provide a higher MCOV and allow 

the arrester to survive the loss of neutral in a 1201240-V system. 

4.2 Experimental verification 

To demonstrate that it. is possible to obtain a satisfactory 

coordination, we used our replica of a residential wiring system 

[8], connecting two of its branch circuits, one 4.5 m long, the 

other 36 m long (Figure 1). We then installed a gap-varistor 

combination at the service entrance of the replica and a 

downstream varistor either at the end of the 4.5-m branch circuit 

or at the end of the 36-m branch circuit. Figure 1 shows the 

configuration of the circuit and defines the various current and 

voltages that will be cited in reporting the results. 

Position 

Position 

0 

I panel 

I, : Current delivered by the generator V, : Voltage at arrester 

I, : Current flowing in gapped arrester V, :Voltage of SPD when at O 

I, : Current flowing in SPD when at O V, :Voltage of SPD when at O 

I, . Gurrent flowlng in 5PD when at W YGi ~wltage acirom gap 

Figure 1 - Test circuit for experimental verification of coordination 

between a gapped arrester installed at the service entrance (Position@) 

and an SPD installed at the end of branch circuits (Positions @ or @) 
In our replica, the power wiring uses the conventional 

non-metallic jacket, 2-conductor plus equipment grounding 

conductor (2 mm dia., AWG #12). The gapped arrester, suitable 

for a 1201240-V system voltage, consisted of a varistor in series 

with a gas tube. The downstream SPD was a typical varistor 

used in plug-in SPDs, rated 130 V rms [15], [16]. 

The surge, applied at the service entrance of the replica, 

was produced by a generator capable of delivering a 6 kV, 

1.2150 ps open-circuit voltage or a 5 kA, 8/20 ys short-circuit 

current, as described in IEEE C62.41-1991 [17]. Suitable t 

differential voltage probes and current-viewing transformers 

were used to monitor voltages and currents during a surge 

event. Tests were conducted in accordance with procedures 

described in IEEE C62.45-1987 [18]. Instruments used for 

measurements are listed in the appendix, which also includes, 

as a contribution toward the updating of C62.45, examples of 

pitfalls in interpretation of digital oscilloscope recordings. 

Aware of the fact that the critical point for coordination is 

not the maximum surge current that may be encountered in the 

application, but some intermediate current for which the 

transition occurs as the gap first sparks over, we sought that 

transition point for each of the line lengths considered in the 

experiment. We would expect that in the case of the short 

decoupling line, it would be more difficult to produce coordination for a given combination of downstream limiting voltage 

and gap sparkover, as the inductive drop would be smaller than 

in the case of the longer line. Nevertheless, we made both 

experiments because the long line, for which coordination is 

easier, creates other problems, as we will see later. 

Figures 2,3, and 4 show respectively, for the case of the 

long branch circuit, the transition from no gap sparkover to gap 

sparkover, occurring first on the tail of the wave, then on the 

front of the wave as the impinging surge current is raised. 

In Figure 2, the 700-V voltage developed across the 

arrester is insufficient to sparkover the gap, and all the applied 

current (140 A peak) goes to the downstream varistor. In the 

experiment where the current I, reflects the interaction of the 

circuit with the generator, the current is reduced by the 

impedance of the long branch circuit; compared with the larger 

1, (440 A) of Figure 3 after gap sparkover. In the real world 

where the impinging surge is a current source, there would not 

be that reduction of the surge current and all of the impinging 

current, unimpeded, would be forced into the downstream 

varistor and flow in the branch circuit, an EMC problem [8]. 

t The measurements reported in this paper have been made with 

&~r,-,t,r;~, f wJ&-1% Ae --b;,,,d -,,ta;mty should mot ,eed 

k5% to 6%. Given the process of applying the measurement results 

to the response of surge-protective devices exposed to environments 

with characteristics that are at best known within an order of 

magnitude, this level of uncertainty does not affect the practical 

conclusions. 

Certain commercial instruments are identified in the appendix list of 

instrumentation in order to adequately describe the test procedure. 

Such ident$cation does not imply recommendation or endorsement by 

the National Institute of Standards and Technology, nor does it imply 

that these instruments are necessarily the best for the purpose. 

From top to bottom traces (5 psldiv sweep): 

V, - 200 Vidiv: 700 V peak 

I, - 100 Ndiv: 140 A peak 

I, - 100 Ndiv: No current in arrester 

l3 - 100 Ndiv: 140 A peak (= lo) 

Figure 2 - Voltage and currents for a surge producing 

a voltage lower than gap sparkover (long branch circuit) 

In Figure 3, the 750-V level developed across the arrester 

is sufficient to cause sparkover of the gap, but still in the tail of 

the wave, 4 ps into the surge. This sparkover transfers the 

impinging current to the upstream arrester, limiting the rise of 

current into the downstream varistor at 65 A instead of 140 A. 

The only stress left on the downstream varistor is to 

slowly discharge the energy stored in the 36-m branch circuit by 

the initial rise of current. Note the sudden increase in I, at 4 ys 

as the load impedance presented to the generator changes from 

36 m of cable to the short path between generator and upstream 

arrester. 

From top to bottom traces (5 psldiv sweep): 

V, - 200 Vldiv: 750 V peak 

I, - 200 Ndiv: 440 A peak 

I, - 200 Ndiv: 380 A peak 

I, - I00 Ndiv: 65 A peak 

Figure 3 - Voltage and currents for a surge producing a 

voltage causing gap sparkover on the tail (long branch circuit) 
With the current rise shut off in the downstream varistor 

as the upstream arrester starts conducting, the current in the 

downstream varistor is then limited to 65 A: a greater surge 

current results in less current in the downstream varistor after 

the transition of current levels from no gap sparkover to gap 

sparkover: "more begets less! " [19]. 

In Figure 4, the larger applied surge (1450 A) results in 

the gap sparking over on the front of the wave, with very little 

delay to allow only the beginning of current build-up in the 

downstream varistor. However, the higher voltage after sparkover (400 V, compared to 350 V in Figure 3) produces further 

increase in the current I, an increase that does not stop until the 

voltage V, falls below 350 V, 15 ps into the surge. This figure 

was recorded to show the complete event, including the end of 

the current pulse, and provide a comparison with Figure 2 and 

Figure 3 at the same sweep rate. As discussed in the Appendix, 

the sharp spike at the front of the voltage trace must arouse 

suspicions that the digital oscilloscope might have missed the 

peak because the need of displaying a 50 ps window means that 

the resulting sampling rate, reflecting the memory size, is not 

sufficient to resolve the peak. The value of this figure is then 

limited to indicating current values and the timing of events, but 

not the peak of the voltage spike. 

.. i 

From top to bottom traces (5 psldiv sweep): 

V1 - 200 Vldiv: Not resolved - See Appendix 

I, - 500 Ndiv: 1450 A peak 

I, - 500 Ndiv: 1400 A peak 

I, - 100 Ndiv: 50 A peak 

Figure 4 - Timing of sparkover and currents for a surge producing 

sparkover of the gap on the front of the wave (long branch circuit) 

Turning now to the case of the SPD connected at the end 

of the short (4.5 m) branch circuit, Figure 5 shows the transition 

from no sparkover to sparkover. In this example, the sparkover 

occurs early in the tail of the wave. Instead of the spike shown 

in Figure 4, the occurrence of the sparkover in the tail provides 

swffi~ient data pints to obtain a valid display of the voltage. 

In this more difficult coordination scenario (smaller 

decoupling impedance afforded by the short branch circuit), the 

build-up of the current I, in the downstream varistor is greater 

than for the case of the Iong branch circuit. 

From top to bottom traces (5 psldiv sweep): 

V, - 200 Vldiv: 840 V peak 

I, - 500 Ndiv: 1010 A peak 

I, - 500 Aldiv: 780 A peak 

I, - I00 Ndiv: 230 A peak 

Figure 5 - Voltage and currents for a surge causing 

gap sparkover into the tail (short branch circuit) 

In Figure 5, the current I, reaches 200 A before the 

arrester shuts off the fast increase, about 2 ps into the event, 

leaving the current with only a modest increase to 230 A before 

it slowly decreases, half-way into the surge event. Thus, the 

stress caused by the energy deposition into the downstream 

varistor is greater than for the case of the long branch circuit. 

Even so, it is still acceptablle for the 20-mrn diameter varistor 

typically used for plug-in SPDs [Ill. Note also the ringing 

visible as the voltage V, reaches its maximum (840 V), resulting 

from the oscillation of the open-ended 36-m branch circuit. 

The appearance of ringing noted in Figure 5 serves as a 

warning that the propagation of surges is not a simple matter 

1201. To give an example of such complexity, and to give an 

answer to the frequently asked question "do we need an SPD on 

each branch circuit, or is one sufficient ?" Figure 6 shows the 

voltage V, at the end of the 36-m branch circuit (Position O, 

Figure 1) during a surge scenario similar to that shown in 

Figure 5 (one only downstream SPD located at Position O, 

none in Position @). 

In the scenario of Figure 6, the long branch circuit was 

left open at Position @, producing a ringing caused by 

reflections and undamped oscillations at that end. In this test, 

the driving voltage V, developed at the upstream gapped arrester 

(Position a) is only 730 V, but the voltage at the end of the 

long branch circuit (Position O) exceeds 1100 V during the 

ringing. Note that for an actual installation, a load connected at 

Position O, where an SPD would be present in this scenario, 

would not be subjected to this relatively high voltage ringing. 

At Position @, a load that would be connected at the end of the 

long branch circuit assumed to be without SPD, where the 

ringing occurs, is likely to damp out the ringing. 

To validate Ihis expectation, we connected CI rcsistivc. load 

at the end of the 36-m branch circuit (Position@), showing that 

the ringing can be considerably reduced, if not completely 

eliminated. An unloaded branch circuit, by its very definition, 

raises no concern for equipment since none is present. 
A light load, such as a solid-state control circuit during the 

off-state of the controlled load, would be the worst case by 

being at the same time a light load and potentially the most 

vulnerable type of load. 

This situation provides an incentive for the so-called 

"whole-house protection" where, as mentioned in Section 11, a 

service-entrance arrester as well as plug-in SPDs are provided 

as a complete package. It is this package approach that will 

make possible the specification, and actual implementation, of 

a coordinated gapped arrester and simple varistor plug-in SPDs. 

Table 1 shows, for a range of load resistances, how the 

oscillations (recorded during our tests with a narrow window as 

discussed in the appendix but not shown here, to limit the 

length of the paper) are reduced as the load resistance is 

decreased. The large decrease from 500 Q to 100 Q occurs 

because above 125 8, the characteristic impedance of the line 

[21], a voltage enhancement occurs while below, a voltage 

reduction occurs. 

From top to bottom traces: 

V, - 200 Vldiv: 730 V peak 

V, - 200 Vldiv: Peaks not resolved - See Table 1 

I, - 500 Aldiv: 750 A peak 

(5 psldiv sweep) 

Figure 6 - Voltages at the service entrance and at the end of a long 

open-ended branch circuit for a sparkover occurring in the service . 

entrance arrester 

TABLE 1 

PEAK OF THE RINGING VOLTAGE AT THE END OF THE 36-m 

BRANCH CIRCUIT AS A EONCTION OF THE CONNECTED LOAD. 

Load, i2 open 10 k 5 k I k 500 100 50 

Peak, V 1170 1170 1150 1020 920 680 650 

4.3 Modeling the experiment 

A numerical model of the wiring was developed with the 

EMTP code [22] for the equivalent parameters of the circuit, as 

measured in our replica of residential wiring [8]. The "Line 

Constants" subroutine of EMTP was used to generate various 

models which were subsequently used in the main data file to 

compute the response of the circuit to various surge waveforms. 

A time step of 0.01 ps was used for the EMTP simulation [23]. 

Experimentally recorded waveforms of surge current were 

digitized. Using the least-squares fitting technique, parameters 

for the current source were determined. Using the "Freeform 

FORTRAN" expression capability of the EMTP code, any 

surge current waveform that can be expressed as a closed form 

equation can be modeled. 

This capability provides a powerful tool for analyzing 

circuit response to various other surge waveforms now under 

consideration by standards-writing organizations. 

The characteristics of the varistors are represented by a set 

of I-V points derived from published characteristics [15] and 

verified by measurements at several current values. In our first 

approximation, the gap is represented by a switch that closes 

when the voltage across it reaches 1100 V. In the future, we 

plan to increase the sophistication of the model by adding an arc 

voltage to the gap characteristic and the presence of fuses to be 

provided as the disconnector device required by the SPD 

standards now being developed. 

The equation used for the impinging current is a damped 

sine wave that allows a close approximation of the current 

delivered by typical Combination Wave generators into 

inductive loads [13]. It is known that actual generators tend to 

produce an "undershoot" when connected to an inductive load, 

and this case was no exception. However, computational 

artifacts occur when using a simple damped sine wave because 

its di/dt derivative (a cosine) is not zero at time zero. Furthermore, we know that nature does not allow an instantaneous 

jump of current from zero to a steep rise. By adding a 

multiplier term [1 - e (-t)], these artifacts are eliminated and the 

waveform has a "gentle toe" [19] which is a better model of 

reality. This improved equation is then: 

I = 2121 * sin(0.126t) * e(t'26.1) * [I- e(-t)] (1) 

with I in amperes and t in microseconds. 

Figures 7 and 8 show plots obtained from modeling the 

same case as that of Figure 4, that is, the application of a surge 

current such that sparkover of the gap will occur on the front of 

the wave. Figure 7 shows the voltage V,, similar to the timestretched trace of Figure A.2 in the Appendix. 

Figure 7 - Model plot of the voltage across arrester, for conditions 

similar to those of Figure 4. (See also Figure A.2 in the Appendix) 
I, - 500 Ndiv; - 1400 A 

I, - 500 Ndiv : 1350 A 

I, - 100 Ndiv : 50 A (Change of scale by plotting software) 

Figure 8 - Model plot of currents, for conditions similar to Figure 4 

Figure 8 shows the three current traces, similar to the 

current traces of Figure 4. The top trace is the applied surge, 

1400 A, postulated according to Eq. (1) to match the current 

involved in the measurement of Figure 4. Practically the same 

peak values are obtained for the resulting currents, respectively 

1300 A for the current in the arrester, I,, and 50 A for the 

current in the downstream SPD, 13. (Note that to present the 

three traces on the same software-driven plot, the l3 trace is 

scaled by a factor of five, to fit the 500 Aldiv versus 100 Ndiv 

of the respective scales of Figure 4). 

4.4 Other important factors 

The objective of this paper, as stated in the introduction, is 

only to show how the dilemma of cascade coordination might be 

resolved by recourse to a gapped arrester at the service entrance. 

We have shown that effective coordination becomes possible by 

appropriate selection of the limiting voltages of the varistors and 

of the gap sparkover characteristics. However, there are other 

factors that will need to be addressed by designers before this 

approach can be transitioned to viable hardware. We have not 

attempted at this stage to study in detail all of these factors, but 

suggest the following list of topics for consideration. 

These are familiar to arrester manufacturers and this list is 

not intended to tutor them, but simply to place the idea in 

perspective so that no false expectations are raised that an 

immediate and easy solution is already at hand. We will have 

accomplished our purpose if the old idea is just given new 

consideration. Among the topics to be studied, the following are 

most important: 

- Ability of the varistor to reduce the follow current to a level 

that will allow the gap to clear at the first current zero - as 

postulated. 

- Ability of the varistor to conduct the follow current that the 

power system can deliver at the point of installation. 

- Ability of the gap to withstand the unavoidable powerfrequency overvoltages of the power system without going 

into conduction and yet to have an acceptable sparkover 

voltage. 

V. THE NEW OPPORTUNITY 

The results of our experimental measurements, which can 

be expanded by parametric modeling, show how a happy state 

of affairs - an effective coordination of cascaded SPDs - 

could be obtained by gapped arresters at the service entrance. 

These arresters would combine the best of the two technologies, 

gas tubes and metal-oxide varistors. This will not happen, 

however, if the decision is not made to apply such a gapped 

arrester. That decision must be made by utilities and installers. 

In contrast, the de facto situation inside the building, imposed 

by millions of installed appliances, is now hopelessly 

immovable. Typically, when these appliances include a built-in 

SPD or, when the end-user purchases and installs an add-on, 

plug-in SPD, these SPDs are of the type with low limiting 

voltage [5], resulting in difficult if not impossible coordination. 

This very difficult coordination, however, should not be 

construed as a recipe for disaster. The reality of the present 

situation is that these low limiting voltage SPDs manage in 

general to survive even in the absence of a service entrance 

arrester. As discussed earlier, this is not a desirable situation, 

hence the proposals for whole-house surge protection. But if 

the proposed service entrance arrester were designed to use a 

simple varistor with ratings commensurate with utility practices, 

it is most likely that the internal SPDs will "protect" the service 

entrance arrester, which then serves no useful purpose and is a 

waste of resources. Furthermore, as more electronics and 

equipment with low logic voltages are installed, the existing 

practices may lose effectiveness. 

Standards or regulations cannot prescribe the particular type 

of service entrance arresler (furthermore, the provision of a 

service entrance arrester is required in only a few countries), so 

the decision is left to the community of utilities, SPD 

manufacturers and end-users. The manufacturers would 

probably respond to the need for gapped arresters if informed 

system designers were to call back from retirement the 'ancient' 

gapped device and, with appropriate technology update, give the 

old idea a new lease on life. 

VI. CONCLUSIONS 

1. The dilemma of coordjnating a cascade of surge-protective 

devices can be solved by providing a gapped arrester at the 

service entrance, that will coordinate with the de facto 

situation inside the building. 

2. The need for a service-entrance arrester to withstand the 

scenario of lost neutral can be satisfied by a gapped arrester 

having sufficient maximum continuous operating voltage 

capability. 

3. Experimental verification of this coordination has been 

demonstrated for typical branch circuit lengths and limiting 

voltages applicable to the 1201240-V systems used in residential applications in North America. The same principles 

can be applied to other power systems with appropriate 

adaptation of voltage ratings and careful consideration of the 

local grounding practices. 
4. The behavior of a complex system such as the interactions 

between circuit impedances and the nonlinear characteristics 

of surge-protective devices can be successfully modeled to 

allow parametric studies. 

5. Other factors need attention, for which good engineering 

practice applied by surge-protective device manufacturers can 

provide adequate design. 

6. While the idea appears sound, it cannot be implemented by 

individual end-users. It will take an initiative by a centralized 

organization, such as the utility serving the district, to 

persuade manufacturers that a market opportunity exists to 

which they can contribute. 

VII. ACKNOWLEDGMENTS 

Support for the development of this revisited approach was 

provided by the Power Quality Research groups of Delmarva 

Power & Light and of Pacific Gas & Electric. Support for the 

testing and modeling was provided by the Electric Power 

Research Institute. 

VIII. REFERENCES 

1. Matsuoka, Masyama & Ida, Supplementary Journal of Japanese Society 

ofApplied Physics, Vol 39, pp 94-101, 1970 

2. Harnden, Martzloff, Morris, and Golden, "Metal-oxide Varistor: a New 

Way to Suppress Transients," Electronics, October 1972. 

3 Sakshaug, Kresge, and Mlske, "A New Concept in Station Arrester 

Design," IEEE Transactions-PES-96, MarchlApril 1977. 

4. Martzloff, "Transient Overvoltage Protection: The Implications of New 

Techniques," Proceedings, EMC Zurich 1981. 

5. UL Standard 1449, Transient Voltage Surge Suppressors (1980). 

6. Martzloff and Leedy, "Selecting Varistor Clamping Voltage: Lower Is 

Not Better!" Proceedings, EMC Zurich 1989. 

7 Key, Mansoor, and Martzloff "No Joules for Surges: Relevant and 

Reahtic Assessment of Surge Stress Threats," Proceedings, 7th 

International Conference on Harmonics and Quality of Power, Las 

Vegas, September 1996. 

8. Key and Martzloff, "Surging the Upside-Down House: Looking into 

Upsetting Reference Voltages," Proceedings, PQ.4'94, Amsterdam, 

October 1994. 

9. IEC Publication 664, Insulation coordination within low-voltage 

systems, including clearances and creepage distances for equipment, 

1980. 

10. Standler, "Coordination of Surge Arresters For Use on Low-voltage 

Mains," Proceedings, EMC Zurich 1991. 

11. Lai and Martzloff, "Coordinating Cascaded Surge-protective Devices: 

High-Low vs. Low-High," Conference Record. IEEE-IAS Meeting, 

October 1991. Also in IEEE Transactions, IAS 29-4 1993. 

12. Hostfet and Huse, "Coordination of Surge Protective Devices in Power 

Supply Systems: Needs for Protection," Proceedings, ICLP 1992. 

13. Hasse, Wiesinger, Zahlmann and Zischank, "Principle for an Advanced 

Coordination of Surge Protective Devices in Low Voltage Systems," 

Proceedings, ICLP 1994. 

14. Rousseau and Perche, "Coordination of Surge Arresters in the LowVoltage Field," Proceedings, 17th International Telecommunications 

Conference (INTELEC 93, 1995. 

15. Transient Voltage Suppression Devices, Harris Corp., 1990. 

16. IEEE C62.33-1982 (Reaffirmed 1989). IEEE Standard Test Specifications,for Varistor Surge-Protective Devices. 

17. IEEE C62.41-1991, IEEE Recommended Practice on Surge Voltages 

in Low-Voltage AC Power Circuits. 

18. IEEE C62.45-1992, IEEE Guide on Surge Testing for Equipment 

Connected to Low-Voltage AC Power Circuits. 

19. Mansoor and Martzloff, "Driving High Surge Currents into Long 

Cables: More Begets Less," IEEE Transactions PWRD 12, No.3, July 

1997. 

20. Goedde, Dugan and Rowe, "Full Scale Lightning Surge Tests of 

Distribution Transformers and Secondary Systems," IEEE - PES 

Transmission and Distribution Conference Record, Dallas TX, 

September 1991. 

21. Martzloff and Gauper, "Surge and High-Frequency Propagation in 

Industrial Power Lines," IEEE Transactions IA-22, July 1986. 

22. EPRI, "Electromagnetic Transients Program (EMTP), Version 2.0; 

Volume 1; Main Program; Volume 2: Auxiliary Routines" EPRI 

Report EL-6421-L, July 1989. 

23. Martzloff, Mansoor, Phipps and Grady, "Surging the Upside-Down 

House: Measurements and Modeling Results," Proceedings, PQA'95 

Conference, EPRI, 1995. 

Arshad Mansoor (M' 1995) is an 

Electrical Systems Engineer at the EPRI 

Power Electronics Applications Center 

(PEAC). He received his MS and Ph.D. in 

electrical engineering from the University of 

Texas, Austin in 1992 and 1994 

respectively. His areas of interest include 

Power Quality, power systems transients 

analysis, harmonics, surge propagation and 

protection, and EMTP model development. 

Franqois Martzloff (M'1956, F' 1983) 

Born and educated in France, with 

additional MS degrees from Georgia Tech 

and Union College, worked at General 

Electric for 29 years and now 12 years at 

the National Institute of Standards and 

Technology. He is contributing to several 

committees for the development of 

standards on EMC, surge protection and 

Power Quality in the IEEE and the IEC. 

Kermit Phipps is in charge of testing and 

evaluating equipment performance in 

accordance with standards of ANSI, IEEE, 

IEC, Military, UL, and the EPRI System 

Compatibility Test Protocols. At PEAC, he 

has conducted laboratory investigations of 

lamp ballasts, surge-protective devices, 

unintermptible power supplies, and personal 

computers. He is the author of test protocols 

and research papers on surge propagation 

and power quality. 

THE ROLE

AND STRESS

OF SURGEPROTECTIVE

DEVICES

IN

SHARING

LIGHTNING

CURRENT
Most simulations performed to investigate the sharing (dispersion) of lightning current for the case of a direct flash 

a building have focused on the role and stress of surge-protective devices (SPDs) installed at the service entrance 

a building and their involvement in that part of the lightning current that exits the building via the power supply 

connection to the energy supply. 

The numerical simulations performed for this paper, based on a postulated waveform and amplitude suggested by 

current standards, include downstream SPDs, either incorporated in equipment or provided by the building occupa

The results show that a significant part of the exiting lightning current can involve those downstream SPDs with so

likelihood that their surge withstand capability might be exceeded. Such a possibility then raises questions on the 

validity of the postulated amplitude in the face of the relatively rare occurrence of reported failures. 

Filename: Role of SPDs
THE ROLE AND STRESS OF SURGE-PROTECTIVE DEVICES 

IN SHARING LIGHTNING CURRENT

François D. Martzloff 

National Institute of Standards and Technology 1

Gaithersburg MD 20877 USA 

f.martzloff@ieee.org

Arshad Mansoor 

EPRI PEAC Corp. 

942 Corridor Park Blvd 

Knoxville TN 37932 USA 

 

1 Contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.

Abstract – This paper examines the sharing of lightning current associated with a direct flash to a 

building. This sharing involves not just those surgeprotective devices (SPDs) that might be installed at the 

service entrance, but also all SPDs involved in the exit 

path of the lightning current. Such sharing might 

involve built-in SPDs of some equipment located close to the service entrance, but heretofore not included in 

numerical simulations performed by many researchers. From the numerical simulations reported in this paper, 

conclusions are offered that may influence the design 

and EMC testing of equipment, as well as the risk 

analysis associated with lightning protection. 

I. BACKGROUND AND RATIONALE 

This paper offers additional information to the body of 

knowledge accumulated on how the lightning current of a direct flash, injected into the earthing system of a building, is shared among the many available paths 

towards intended or opportunistic earthing electrodes. 

Recent developments in the International Electrotechnical Commission (IEC) and the Surge-Protective 

Devices (SPD) Committee of the Institute of Electronics 

and Electrical Engineers (IEEE) have focused on the role of SPDs connected at the service entrance of a 

building in the case of a direct lightning flash to the 

building. This scenario is described in IEC 61312-3 

(2000) [9], IEEE PC62.41.1 [12] and PC62.41.2 [13]. 

Prior to this new focus, most of the considerations on 

SPD applications were based on the scenario of surges 

impinging upon the service entrance of a building as 

they come from sources external to the building. The new (additional) focus addresses the scenario of the 

earth-seeking lightning current as it is shared among the 

many possible paths to earth, including the deliberate 

and opportunistic exit paths of the building earthing 

system, services other than the power system 

connection and, mostly, the power supply connection. 

Quite independently from these lightning protection 

considerations, the IEC Subcommittee SC77B had 

developed a series of documents on the electromagnetic 

compatibility of equipment, IEC 61000-4-5, Surge 

withstand capability [8] in particular. These documents 

were primarily concerned with immunity against typical 

disturbances, the rare case of a direct lightning flash to a 

building containing electronic equipment not included. 

Increasing recognition of the need to include the 

scenario of a direct flash to a building – rare as it might 

be – has motivated the formation of an IEC Joint Task 

Force TC81/SC77B for the purpose of conside

surge stresses on equipment higher than those curre

described in the IEC document 61000-4-5 on immu

testing [8]. 

The purpose of the paper is to examine in detail 

sharing of lightning current, not just by the SPDs at 

service entrance, but also by all SPDs that might 

involved in the exit path of the lightning current. S

sharing might well involve SPDs incorporated in 

equipment located close to the service entrance, but 

always included in the numerical simulations that h

been performed by many researchers (Altmaier et 

1992) [1]; (Standler, 1992) [23]; (Rakotomalala, 19

[20]; (Birkl et al., 1996) [3]; (Mansoor and Martzl

1998) [15]; (Mata et al., 2002) [19]. In its re

development of a Guide and a Recommended Prac

on surges in low-voltage ac power circuits [13] 

IEEE has refrained from identifying SPDs as be

those that may be connected at the service entra

Instead, it refers to "SPDs involved in the exit p

without reference to their point of installation. 

Given the tendency of equipment manufacturers 

include an SPD at the equipment power input port, 

issue of "cascade coordination" arises. Several prev

papers (Martzloff, 1980) [17]; (Goedde et al., 19

[5]; (Lai and Martzloff, 1991) [14]; (Standler, 19

[22]; (Hostfet et al., 1992) [7]; (Hasse et al., 1994) 

have explored the concept of cascade coordina

involving two or more SPDs connected on the s

power supply but at some distance from each other. 

The legitimate wish of the energy service provider

specify robust SPDs at the service entrance result

SPDs having a relatively high Maximum Continu

Operating Voltage (MCOV). On the other hand, so

equipment manufacturers tend to select SPDs wit

low MCOV under the misconception that lower is be

(Martzloff and Leedy, 1989) [18]. This dichotomy 

result in a situation where the low-MCOV S

included in equipment might well become involve

the "exit path" and thus become overstressed in the c

of a direct flash to the building. This situation is m

more complicated by the fact that commercial S

packages are assembled from typical distribut

supplies that can have an allowable tolerance band 

±10% on the voltage-limiting rating. 

To explore the possibility and implications o

questionable coordination, numerical simulations w

performed on a simplified model of a building featu

SPDs installed at the service entrance and SPDs 

may be incorporated in equipment connected inside 

building near the service entrance. 
II. NUMERICAL SIMULATIONS 

II.1 Basic circuit 

Figure 1 shows a simplified building power system that 

includes the key elements of this scenario: the building 

earthing system and all earthing electrodes, with the 

corresponding exit paths via the service-entrance SPDs 

and a built-in SPD provided at the power port of a 

typical item of electronic equipment. In this example, 

these SPDs are metal-oxide varistors (MOVs) with 

typical voltage ratings (150 V at the service entrance 

and 130 V in the equipment) selected for a 120/240 V 

residential power system. (The conclusions obtained 

for this type of power system will also be applicable to 

240/400 V systems.) 

Numerical analysis of the circuit behavior by EMTP [4] 

allows inclusion of the SPD characteristics as well as 

the significant R and L elements of the wiring, with 

injection of a stroke current of 100 kA 10/350 μs at any 

selected point – the earthing system in this case. The 

selection of a 100 kA peak is consistent with the 

postulate made in many published simulations, but 

might be questioned on the basis of field experience and 

lightning detection statistics, as will be discussed later 

in this paper. 

In Figure 1, the neutral is defined as part of a "multiplegrounded neutral" system (TN-C-S), with distributed R 

and L elements between its earthing electrode 

connections. The R and L values for the cables used in 

the numerical simulation, but not shown in the figure to 

avoid clutter, were selected to emulate the typical wire 

diameters used in low-voltage power distribution 

systems and building installations. 

Previous studies (Birkl et al., 1996) [3]; (Mansoor 

Martzloff, 1998) [15] have validated the intui

expectation that the tail of the 10/350 μs wavef

often postulated for simulations will be shared am

the available paths simply according to the rela

values of resistance in the paths leading to the earth

electrodes. This fact is apparent in the results of Fig

2, for example at the 350 μs time: when induc

effects have dwindled, the current IH in the 1

earthing resistance of the building is ten times sma

than the total current exiting the building [IN+IL1+

toward the power distribution system in which mult

earthing electrodes offer an effective earthing resista

of only 1 Ω. It is also worthy to note that this sharin

controlled by the relative values of the resistances

that any earth conductivity differences associated w

local conditions will wash out. 

The combination of the service-entrance 150-V M

on Line 2 and the 130-V MOV incorporated at 

power port of the equipment constitutes a so-ca

"cascade". When two such cascaded SPDs are to 

coordinated, a decoupling impedance must be provi

between the two SPDs so that the voltage drop cau

by the current flowing in the decoupling impedance 

this example the impedance of the 2,5 mm2

 diam

wires – and added to the limiting voltage of the 13

MOV, will cause enough of the current to flow thro

the 150-V MOV to reduce stress on the 130-V MOV

The simulation was performed for three values of 

impedance (length) of the connection, i.e., 0,1 m, 1 

and 10 m to assess the effect of this impedance 

practical situations. Figure 3 shows the results 

these three cases and Table 1 shows the resulting ene

deposition in the respective MOVs.

Figure 1 Simplified building schematic with service-entrance SPDs, one built-in equipment SPD, and 

multiple-grounded power distribution system in case of a direct lightning flash to the earthing system
0

20

40

60

80

100

120

0 100 200 300 400 500

IN

IH IL1 & IL2

Io (100 kA 10/350)

Legend 

IO: 100 kA, 10/350 μs stroke to the building earthing system 

IN: current exiting via the neutral of the power supply 

IL1, IL2: current exiting via the two lines of the power supply 

IH: current into the building earthing electrode(s) 

Vertical scale: current in kA – Horizontal scale: time in μs

Figure 2 – Sharing of the lightning current among 

available paths to earth electrodes 

In the traces of Figure 3, the total current in Line 2 (sum 

of the two currents in the two MOVs) remains 

essentially unchanged for the three combinations, but 

the sharing of the current between the two MOVs is 

significantly affected. 

Figure 3a, with only 0,1 m of separation, is not a 

practical example of connection of equipment that close 

to the service entrance – except perhaps an electronic 

residual current device incorporated in the service 

panel. The two other figures, 3b and 3c, show how the 

130-V MOV that took the largest part of the current in 

the case of Figure 3a, now takes on less as separation 

length increases. An interesting situation develops as 

the current flowing in the 10-m line to the 130-V MOV 

stores energy that will cause a stretching of the current 

in the 130-V MOV long after the 150-V MOV current 

has decayed. This is significant because the total 

energy deposited in the MOVs is the criterion used for 

coordination, even though the current in the 130-V 

MOV could be lower than the current in the 150-V 

MOV. Table 1 shows how this energy sharing changes 

with the length of the decoupling connection, according 

to the integration of the varistor currents and voltages 

obtained from EMTP. 

Table 1 – Sharing energy between MOVs 

for three different connection lengths 

Energy deposition (joules) SPD 0,1 m 1 m 10 m 

150-V MOV 620 1090 2470 

130-V MOV 2560 2030 890 

These energy levels might be acceptable for a 150-V 

MOV sized for service entrance duty, but the 890-joule 

deposition into the 130-V MOV incorporated in the 

equipment exceeds common-wisdom ratings for such 

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000

IL2

Ie

IS2

a) 0,1 m connection 

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000

IL2

IS2

Ie

b) 1 m connection 

0

2

4

6

8

10

12

14

16

18

0 500 1000 1500 2000

IL2

IS2

Ie

c) 10 m connection

Legend 

IL2: current exiting via the power supply phase conductor 

IS2: current into the service entrance SPD 

Ie: current into the equipment SPD 

All vertical scales: current in kA 

All horizontal scales: time in μs

Figure 3 – Sharing of lightning stroke current 

devices. This finding then raises a question on 

effectiveness of a cascade for the case of direct flas

the building. In an actual installation, there would 

more than one piece of equipment, presumably e

with a 130-V built-in MOV at the power port. 

might expect that some sharing among these mult

SPDs would reduce the energy stress imposed on th

devices. 
To explore this situation, an additional simulation was 

performed for three branch circuits, respectively 10 m, 

20 m, and 30 m, each of them supplying equipment 

incorporating a built-in 130-V MOV. Figure 4 shows 

the sharing of current among these three MOVs and the 

150-V service entrance MOV, and Table 2 shows the 

energy deposition. 

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000

IS2

Ie(10m) Ie(20m Ie(30m)

Legend 

IS2: current into the service entrance SPD 

Ie: currents in the three SPDs at end of 10, 20, and 30 m lines 

Vertical scale: current in kA – Horizontal scale: time in μs

Figure 4 – Sharing of current among MOVs 

Table 2 – Energy sharing among MOVs 

Branch circuit length and energy 

deposition into three 130-V MOVs 

10 m 20 m 30 m 

Service entrance 

150-V MOV 

620 J 370 J 280 J 1930 J 

 

II.2 Effect of manufacturing tolerances on 

commercial-grade metal-oxide varistors 

The simulations discussed so far were performed by 

postulating that both the 150-V MOV and the 130-V 

MOV had their measured voltage limiting at the 

nominal value as specified by typical manufacturer 

specifications. Such a postulate is of course difficult to 

ensure in the reality of commercial-grade devices. For 

instance, the nominal voltage-limiting value of MOVs 

rated 130 V rms is 200 V, with lower limit of 184 V and 

upper limit of 220 V. To check that aspect of the 

problem, an arbitrary lot of 300 devices rated 130 V rms 

was purchased from a distributor and the actual 

measured voltage-limiting value at 1 mA dc was determined in accordance with IEEE Std 62.33-1994 [11]. 

For this lot, the standard deviation (sigma) was found to 

be 8 V. 

 

On the basis on these measurements and to give an 

indication of the significance of tolerance effects, the 

computations reported for Figure 3c (10 m separation) 

were repeated, still with a 150 V MOV at the service 

entrance, but with varistors at ±1 sigma of the 130 V 

rms rating, that is, 122 V and 138 V rms. The results 

are shown in Table 3. 

Table 3 Energy sharing for three values of th

equipment built-in MOV (10 m separation) 

 Equipment Energy deposited (J) 

MOV rating 

(V rms) 

Equipment 

MOV 

150-V service 

entrance MOV 

122 915 2320 

130 890 2890 

138 750 2650 

These results illustrate the significance of tolerance

a situation where the difference between the two S

of the cascade is not large, because of the de f

situation of low values of MCOV that the industry 

unfortunately adopted. Of course, if tolerances w

also taken into consideration for the service entra

MOV, the extremes of distributions for both M

would make an effective coordination betwee

nominal 150-V MOV and a nominal 130-V MOV e

more problematic. 

 

II. 3 Nonlinearity of circuit elements 

 

Most of the reported simulations, as cited above, h

been performed with a conservative postulate of a 

kA 10/350 lightning discharge. The median of 

current peaks compiled in the seminal Berger et 

paper [2] is only 20 kA. Occasional reservations h

been voiced on the validity of these data collected w

technology dating back to the 1970’s. A recent (

2000) actual case history was communicated to 

authors by a colleague for two major lightning sto

recorded in the area of Tampa in Florida by mean

the Lightning Detection System [24], during which o

30 000 flashes were detected in a period of less than 

hours, with only one at the 150 kA level, and a me

of 20 kA, confirming the Berger at al. data. 

One could expect that the dispersion of the lightn

current that results from the combined action of li

elements (resistance and inductance) with nonli

components (MOVs) might produce a different sha

of the current as the decoupling element is linear but 

SPDs are nonlinear. To explore this hypothesis, 

computations for the case of Figure 4 and Table 2 w

repeated, for peak currents of 100 kA (the original v

of the computation), 50 kA, and 25 kA (about 

median of the statistics). Table 4 shows the result

these computations. It is interesting to note that as 

applied stroke is decreased 4 to 1 (from 100 to 25), 

total energy deposited in the varistors is decreased b

factor of 3200/610 = 5.2. This relative greater decr

is caused by the larger portion of the current exiting 

the linear-path neutral, further relief for all the S

involved in the exit path. 

 Table 4 Nonlinear effects on current sharing 

Branch circuit length and 

energy deposited into 

three 130-V MOVs 

10/350

stroke 

(kA) 10 m 20 m 30 m 

Energy 

into 

service 

entrance 

150-MOV 

Tot

ene

in t

MO

100 620 J 370 J 280 J 1930 J 320

50 329 J 215 J 179 J 700 J 142

25 170 J 120 J 90 J 230 J 610 
III. DISCUSSION 

 

We have made all these computations based on 

postulating that the insulation levels are sufficient to 

prevent a flashover that would drastically affect the 

continuing energy deposition in the downstream SPDs. 

We have not included the limits of energy handling of 

the devices, which of course should be compared with 

computed deposited energy levels in a practical case. 

Another set of readings from the EMTP computations 

confirmed that the presence of SPDs at the critical 

points prevents such overvoltages from occurring (as 

long as the SPDs can carry the resulting currents) 

 

Not surprisingly, the results of the simulation confirm 

that the sharing of the lightning current occurs in 

inverse ratio of the resistances leading to the earthing 

electrodes after the initial phase of the 10/350 μs stroke. 

Likewise, one can expect that inductances will limit the 

current flow so that low-inductive paths, such as 

intended and opportunistic earth electrodes of the 

building itself, compared to the longer lines of the 

power supply, will carry a larger share of the total 

current during the initial phase of the current. This 

effect is clearly visible on the IH of Figure 2, for the 

relatively slow rise time of 10 μs of a first stroke. One 

may expect that for the subsequent strokes, or the 

flashes associated with triggered lightning experiments 

that have shorter rise times (Rakov et al., 2001) [21], 

this effect will be even more apparent. 

 

An important finding – predictable on a qualitative basis 

but heretofore not quantified for the case of a direct 

lightning flash to buildings containing electronic 

equipment – concerns the cascade coordination of builtin SPDs in the equipment. From the simple examples 

presented, it appears that a cascade of a robust serviceentrance SPD and a built-in SPD sized for limited 

energy-handling capability, according to the commonwisdom practice, might well be a delusion. 

A solution to the difficult coordination could be to 

replace the all-MOV SPD at the service entrance with a 

combined series gap-varistor device (Mansoor et al., 

1998) [16]. Such a device would also alleviate the 

concerns about the temporary overvoltage problems 

associated with MOV-only SPDs. Sparkover of the gap 

during the initial rise of the lightning current (when the 

coordination by means of the decoupling inductance 

occurs) will invite the remainder (continuing rise and 

tail) of the surge current exiting via SPDs to use the 

service entrance SPD rather than the simple and less 

robust built-in MOVs downstream. 

Last but not least, the practical question remains open 

on the need to provide surge protection against worst 

cases – the combined worst case of a direct flash to the 

building and the high-level 100 kA stroke, which is 

only at the 4% probability, according to the Berger et al. 

data [2] and even lower in the yet-anecdotal case of the 

Tampa Bay lightning storm [24]. The nonlinearity effect 

presented in II.3 adds further credibility to the overall 

need to make reasonable risk assessments of costeffectiveness before specifying high surge level 

requirements, both for the service entrance SPDs and 

for built-in SPDs in connected equipment. 

IV. CONCLUSIONS 

1. When accepting the postulate that the refere

parameter of a direct lightning flash to a building sho

be a 10/350 μs current with a peak of 100 kA, 

numerical simulations performed for a simpli

system with one surge- protective device installed at 

service entrance, and one or more built-in SPD 

downstream equipment indicate that the downstr

SPD is very likely to be overstressed and fail, m

likely catastrophically. 

2. There are several possible explanations for 

apparent contradiction between a prediction of do

stream equipment failures based on this postul

lightning parameters, and equipment field experie

that does not report such frequent failures, although 

course anecdotes abound. 

• The occurrence of a direct flash to a building 

cause such extensive damage that a post-mortem 

investigating the specifics of a prevailing ineffec

coordination is not performed at that time and 

issue is ignored. 

• Enough uncontrolled clearance flashovers occu

the installation to provide significant relief for any 

risk SPDs incorporated in downstream equipment

• In an installation where many built-in or plu

SPDs are present, the sharing illustrated by Figur

combined with a low probability of a 100 kA stro

might reduce the stress on downstream devices 

value within their capability. In particular, m

commercial plug-in SPDs advertise capabilities 

hundreds of joules, unlike the 20 joules of a sin

MOV, which might be provided at the input por

electronic equipment. 

• Insufficient field failure data have been obtain

compiled, shared, and published to enable real

assessment of frequency and severity of occurren

involving an unsuccessful cascade coordination. 

 

3. It is impractical at this point to mandate high ene

handling capability for built-in SPDs. Such a m

might meet with strong objections from manufactu

whose products have satisfactory field experience, an

risk analysis might show it to be not cost-effective. 

4. Economic and political realities related to the t

and mission of the installations to be protected sho

be kept in mind. Clearly, mass-market applicat

such as cost-conscious consumers, in a framework 

regulated or unregulated installations, are different f

bottom-line-conscious industrial applications, and e

more so in the case of national assets – be they cult

or military. 

5. Another approach for manufacturers might be 

avoid placing low MCOV varistors at the input por

their equipment. Rather, they should select an S

with an MCOV and resulting surge-protective leve

high as their equipment can inherently stand. This 

“selfish” approach which is mentioned here h

seriously, half-facetiously: there are enough low MC

SPDs installed by users or included in other equipm

in a typical system that those unfortunate low-MC

devices will take up the stress, leaving unscathed 

equipment wisely provided with high MCOV SPDs! 
V. REFERENCES 

Note: The citations that appear in the text are listed here 

by alphabetical order of the lead author, not by 

chronological order of appearance in the text. 

[1] Altmaier, H., Pelz, D. and Schebe, K., “Computer 

Simulation of Surge Voltage Protection in LowVoltage Systems,” Proceedings, 21st International 

Conference on Lightning Protection, Berlin 1992. 

[2] Berger, K., Anderson, R.B. and Kröniger, H., 

“Parameters of Lightning Flashes,” ELECTRA

No.41, 1975. 

[3] Birkl, J., Hasse, P., and Zahlmann, P., “Investigation 

of the Interaction of Lightning Currents with LowVoltage Installations and Their Related Threat 

Parameters,” Proceedings, 23rd International 

Conference on Lightning Protection, Firenze, 1996. 

[4] EPRI, “Electromagnetic Transients Program,” 

(EMTP), Version 2.0, Vol. 1: Main Program; Vol.2: 

Auxiliary Routines, EPRI Report EL-6421-L, 1989. 

[5] Goedde, G.L., Marz, M.B. and Henry, D.C., 

“Coordinating Lightning Stroke Protection From the 

Utility System to Load devices,” Proceedings, 

Second International Power Quality /ESD 

Conference, October 1990. 

[6] Hasse, P., Zahlmann, P., Wiesinger, J., and 

Zischank, W., “Principle for an Advanced 

Coordination of Surge-Protective Devices in LowVoltage Systems,” Proceedings, 22nd International 

Conference on Lightning Protection, Budapest, 

1994. 

[7] Hostfet, O.T., Hervland, T., Nansen, B., and Huse, 

J., “Coordination of Surge Protective Devices in 

Power Supply Systems: Needs for Secondary 

Protection,” Proceedings, 21th International 

Conference on Lightning Protection, Berlin, 

September 1992. 

[8] IEC 61000-4-5 (2001) Electromagnetic 

Compatibility - Part 4: Testing and measurement 

techniques - Section 5: Surge immunity test.

[9] IEC/TS 61312-3 (2000) Protection against LEMP - 

Part 3: Requirements of Surge Protective Devices.

[10] IEC 61643-1 (2002) Surge protective devices 

connected to low-voltage power distribution systems 

- Part 1: Performance requirements and testing 

methods

[11] IEEE Std 62.33-1994 IEEE Standard Test 

Specifications for Varistor Surge-Protective 

Devices. 

[12] IEEE C62.41.1-2002 Guide On The Surge 

Environment In Low-Voltage AC Power Circuits

[13] IEEE C62.41.2-2002 Recommended Practice o

Characterization of Surges in Low-Voltage AC 

Power Circuits 

[14] Lai, J.S. and Martzloff, F.D., “Coordinating 

Cascaded Surge-Protection Devices: High-Low 

versus Low- High,” IEEE Transactions IA-24, 

No.4, 1993. 

[15] Mansoor, A. and Martzloff, F.D., “The Effect o

Neutral Earthing Practices on Lightning Current 

Dispersion in a Low-Voltage Installation,” IEEE 

Transactions PWRD-13, 1998. 

[16] Mansoor, A., Martzloff, F.D., and Phipps, K., 

“Gapped Arresters Revisited: A solution to 

Cascade Coordination,” IEEE Transactions PWR

13, 1998. 

[17] Martzloff, F.D., “Coordination of Surge Protecto

in Low-Voltage AC Power Circuits,” IEEE 

Transactions, PAS-99, 1980. 

[18] Martzloff, F.D. and Leedy, T.F., “Selecting 

Varistor Clamping Voltage: Lower is not Better 

Proceedings, 8th International Zurich Symposium 

on EMC, 1989. 

[19] Mata, C.T., Fernandez, M.T., Rakov, V.A. and 

Uman, M.A., “EMTP Modeling of a Triggered 

Lightning Strike to the Phase Conductors of an 

Overhead Distribution Line,” IEEE Transaction

PWRD, 2002.

[20] Rakotomalala, A., Rousseau, A., and Auriol, P., 

“Lightning Distribution Through Earthing 

Systems,” Proceedings, IEEE International 

Symposium on EMC, 1994. 

[21] Rakov, V.A., Uman, M.A., Fernandez, M.I., Ma

C.T., Rambo, K.J., Stapleton, M.V. and Sutil, R

“Direct Lightning Strikes to the Lightning 

Protection System of a Residential Building,” IE

Transactions PE-032PRD, 2001. 

[22] Standler, R.B., “Coordination of Surge Arrester

and Suppressors for Use on Low-Voltage Mains

Proceedings, 9th International Zürich Symposium 

on Electromagnetic Compatibility, 1991 

[23] Standler, R.B., “Calculations of Lightning Surg

Currents Inside Buildings,” Proceedings, IEEE 

EMC Symposium, August 1992. 

[24] Waterer, S.F., Personal communication on the 

Lightning Storm in Tampa Bay Area, July 15, 

2000. 
CASCADE

COORDINATION
APPLICATION OF SURGE-PROTECTIVE DEVICES 

AND 

COORDINATION OF CASCADES 

Compiled by Fran~ois D. Martzloff 

September 1992 
2002 REMARKS 

As stated in the Foreword (on following Page 3), this Annotated Bibliography was compiled i

1992 in support of a Working Group of the IEEE Surge-Protective Devices Committee engage

in the development of an Application Guide on Low-Voltage Surge-Protective Devices, and a

IEC project about to be launched, involving five Technical Committees or Subcommittees of t

IEC for developing a “pilot” Technical Report or Standard on the application of low-voltage 

surge protective devices (SPDs), intended in particular to focus on the coordination of cascade

SPDs, an issue that was emerging at the time. To the author’s knowledge, only few additional 

papers were published on the subject after 1992, see the file “Citations Part 8” that is included 

Annex A of this Part 8. 

Both documents IEC and IEEE eventually reached maturity and, ten years later, the IEC has 

published its document, and the IEEE has conducted a ballot on its document. They can be 

obtained from their respective sponsoring organizations: 

IEEE PC62.72-2002 – Guide for the application of surge protective devices for low-voltage 

AC power circuits 

Ballot in progress (December 2002, publication expected mid-2003) 

Abstract: Information is provided to specifiers and users of surge protective devices (SPDs) 

about the application considerations of SPDs associated with power distribution systems 

within North America. This guide applies to SPDs to be connected to the load side of the 

service entrance main over current device of 50 or 60 Hz ac power circuits rated at 100-

1000V rms. The effects and side effects on the presence and operation of SPDs in lowvoltage power distribution systems are described. The coordination of multiple SPDs on the 

same circuit is described.

IEC/TR 62066 (2002-06) – Surge overvoltages and surge protection in low-voltage a.c. 

power systems - General basic information 

Abstract: Presents a general overview on the different kinds of surge overvoltages that can 

occur on low-voltage installations. Typical surge magnitude and duration as well as frequency 

of occurrence are described. Information on overvoltages resulting from interactions between 

power system and communications system is also provided. Additionally, general guidelines 

are given concerning surge protection means and systems on the basis of availability and risk 

considerations, including interactions and the need for coordination and consideration of 

temporary overvoltages in the selection of surge-protective devices. 

1992 ACKNOWLEDGMENT

Only the cooperation of many authors who made available hard copies of their papers, or of th

colleagues’ papers, made this compilation possible. Their help in this venture has been essent

My hope is that in providing this review, I have not misrepresented their ideas. If I did, I take 

full responsibility for an unintentional error and offer my apologies. 
FOREWORD 

In view of the emerging concerns on the likelihood of achieving a successful coordination of cas

surge-protective devices, this bibliography has been compiled to provide as complete informati

possible to the joint efforts underway within the US National Committee for the IEC, as well as w

the transnational community, at the level of the Working Groups of cognizant Technical Committ

This document is organized in two parts: 

1. List of identified documents with retrieval information. Depending on the outcome of req

made to the various pubiishers, hii copies of the documents might be made available to me

of interested Working Groups. 

2. For each document, a single-page digest showing the author's abstract, the author's conclu

a?;! brief ixiiii~t~ti~i-i.~ hiii the ie~i~sei concerning the iinpilc~ib~ilrppii~dtiom of the docu

te the Sidbjed of cacde c~oidiiiZti~ii. 

The 'Reviewer's Annotations' have been added to focus on the issue of cascade coordination

represent the reviewer's Nartzloff) ~oint of view. As such; they are subject to discussion or 

refutation; they were formulated with the objective of stimulating open discussion, not adver

controversy. 

Comments on this bibliography will be welcome, perhaps leading to periodic updates as necessary

possibility might be that annotations contributed by other experts could be included in later issues o

bibliography, leading to a shared document of the Joint Working Group. Suggestions for l

additional documents are invited. 

NOTE: This September 1992 issue has been prepared for the September, 1992 meeting of IEEE SPD WG 3.4.6 and the O

1992 Joint Working Group of IEC SC28A. SC37A, TC64, SC77B and TC81. The deadline for printing and distribution 

impossible to complete all the annotations; the selection of those citations that are annotated does not reflect a systematic in

of ranking papers by order of signif~cance. 

Cascade Bibliography - September 1992 
ALPHABETICAL - CHRONOLOGICAL LISTING OF DOCUMENTS 

ANSIIIEEE C62.41-1991 - Recommended Practice on Surge Voltages in Low-Voltage AC Power Circuits. 

ANSI C84.1-1989 - American National Standard for electric Power Systems and Equipment - Voltage Ratings 

Ua.4.. I XACI b4J. 

Anderson, L.M. and Bowes, K.B. - The Effects of Power-Line Disturbances on Consumer Electronic Equipm

ZEEE Transactions PWRD-5, No.2, April 1990, pp 1062-1065. 

Benda, S . - Znteflerence-free Electronics - Design and Applications. Chartwell-Bratt Ltd., Bromley , U.K., 19

Bird, A.O. - The Effects of Installation Practices on the Performance of Transient Voltage Surge Suppress

Proceedings, Forum on Surge Protection Application, NZSiTR-4657, August 1991, pp 105-116. 

Corbett, M.P. and Wolff, B.I. - Performance of MOV Suppressors in Low-Voltage AC Circuits. Proceedin

Forum on Surge Protection Application, NZSTlR-4657, August 1991, pp 43-50. 

Crouch, K.E and Martzloff, F.D. - Lightning Protection of Residential AC Wiring. Declassified Memo Rep

MOR-78-095, GE Company, 1978. (Available from FD Martzloff) 

Davidson, R. - Suppression Voltage ratings on UL Listed Transient Voltage Suppressors. Proceedings. Forum 

Surge Protection Application, NZSiTR-4657, August 1991, pp 89-92. 

Diigaii, R.C. aid Sriii't, S.D. - Low-VoitageSide Current-Surge Phenomena in Singie-Phase Distribu

T~asfn-mer System. _?reprint TLn 553-2, 1EEE T&n Co::fc"rc"~m, 1986. 

Dugan, R.C., Kershaw, S.S., and Smith, S.D. - Protecting Distribution Transformers from Low-Side Cur

Surges. Preprint 7D 401-1 PWW, ZEEE T&D Conference, 1989. 

Dugan, R.C. - Conduction of Lightning Stroke Currents From the Utility System to Load Devices. Confere

Proceedings, Power Quality, October 1989. 

Dugan, R.C., Goedde, G., and Henry, C. - Conduction of Lightning Stroke Currents From the Utility System 

Load Devices. Conference Proceedings, Power Quality For End-Use Applications, March 1990. 

Dugan, R.C. - Low-Side Surges: Answers to Common Questions. Cooper Power Systems Bulletin SE9001, A

1992. 

Goedde, G.L., Dugan, R.C., and Rowe, L.D. - Full Scale Lightning Surge Tests of Distribution Transformers 

Secondary Systems. (Place of publication unknown) 

Goedde, G.L., Marz, M.B., and Henry, D.C. - Coordinating Lightning Stroke Protection From the Utility Sys

to 'mad Devices. Proceedings, Second internationai Power QuaiityiASD Conference, October 1990, Philadelp

Hairabedian, B. - A survey of Power Line Disturbances at Typical IBM Computer Installations in the U.S. for 

Period 1988-1992. Document Number TR 21.1507, International Business Machines Corporation, Kingston N

June 1992. 

Hasse, P., Wiesiger, I., and Zischank, W. - Isolations-koordination in Niederspannungsanlagen auch 

Blitzeinschlagen. Electrotech. Zeitschr~jl, Jan 1989, pp 64-66. (In German; English translation available from 

Martzloff) 

Hasse, P. - Overvoltage Protection of low-Voltage Systems. IEE Power Series, Peter Peregrinus Ltd. Lond

1992. (Original German edition in 1987) Available in the U.S. from IEEE. 

Hostfet, O.T. et al. - Coordination of surge protective devices in power supply systems: Needs for second

protection. Proceedings, International Conference on Lightning Protection, Berlin, September 1992. 
HUS~, I.P. - Contributions to the revision of Doc 28A(Sec)47, Internal document, ZEC/SC28A WWI

IEC 28A(USAILas Vegas)09 - (Draft) Explanation for over-voltage categories. December 1984, Amen

1987. 

IEC 28A(Norway) - Comments of the Norwegian National Committee on Document 28A(Secretariat)4

IEC 37A/WG3(Convenor)l - DraJi Application Guide, 1992. 

IEC 64lWG3 138A - Explanation of interfaces for overvoltage categories. Supplement to Appendix B of 

November 1990. 

IEC 77(C0) 1 18 Classification of Electromagnetic Environments 

Lagergren, E.S., Martzloff, F.D., Parker, M.E., and Schiller, S.B. - The effect of repetitive swells on 

varistors. Proceedings, PQA 92 Conference, September 1992, pp xx-xx. 

Lai, J.S. - Performance Criteria for Cascading Surge-Protective Devices. Proceedings, Open Foru

Protection Application, NZSllR-4654, August 1991, pp 147-160. 

Lat, M.V. - Determining Temporary Overvoltage Levels for Application of Metal-Oxide Surge A

Multigrounded Distribution Systems. ZEEE Transactions PWRD-5, April 1990, pp 936-946. 

Martzloff, F.D. and Crouch, K.E. - Coordination de la protection contre les surtensions dam les ds

tension rkidentiels. Proceedings, 1978 IEEE Canadian Conference on Communications and Power, 

(In French; English translation available from FD Martzloff) 

Martzloff, F.D. - Coordination of Surge Protectors in Low-Voltage AC Power Circuits. IEEE T

PAS-99, January/February 1980, pp 129-133. 

Martzloff, F.D. - Coupling, Propagation, and Side Effects of Surges in an Industrial Building Wiring Sy

Transactions L4-26, MarchlApril 1990, pp. 193-203. 

Martzloff, F.D. and Lai, J.S. - Cascading Surge-Protective Device.: Coordination versus the IEC 66

Proceedings, PQA 91 Conference, pp 191-198. 

Martzloff, F.D. - On the Propagation of Old and New Surges. Proceedings, Open Forum on Surg

Application, NZSTIR-4654, August 199 1, pp 19-28. 

Martzloff, F.D. and Lai, J.S. - Cascading surge-protective devices: Options for effective imple

Proceedings, PQA 92 Conference, September 1992, pp xx-xx. 

Man, M.B. and Mendis, S.R. - Protecting Load Devices from the Effects of Low-Side Surges. P

ZEEE/ZCPS Conference, May 1992 

b eyer, J.P. - Parafoudres en Cascade. Proceedings, UTE Workshop on Surge Arresters, Paris, Mar

ji French). 

Rousseau, A., Lafon, G., and Malpike, F. - Les parafoudres face aux norrnes. Proceedings, C

International Workshop on EMC, Lyon-Ecully, France, June 1992. (In French) 

Scuka, V. - Application of modern surge suppressors in low-voltage power installation networks. Insti

Voltage Research, Uppsala University, UURIE:250-86, 1986. 

Cascade Bibliography - September 1992 


surge crest voltage at unprotected locations. On an unprotected circuit, the surge voltage is limited by the sparko

of clearances, which for 1201240 volt systems is given as 6 kV or less. This level is considered as a cutoff le

for transients on indoor power systems. The two recommended "standard waveforms" are the 100 WIz Ring wa

and the 1-2/50 - 8/20 Combination Wave. The three suggested "additional waveforms" are the 5/50 ns EFT bur

the 1011OOO voltagelcurrent wave, and the 5 kHz Ring Wave. 

While providing a description of the surge environment that can be expected, the docume

emphasizes that it should not be construed as a surge-withstand requirement standard. 
1.2 Purpose 

The purposes of this standard are: 

(1) To promote a better understanding of the 

voltages that are associated with power 

systems and utilization equipment in order to 

achieve overall practical and economical 

design and operation 

ratings and tolerances 

(6) To provide a guide for future d

and design of equipment in orde

the best possible conformance wit

of the users 

(7) To provide a guide, with respec

of voltages, for new pow

undertakings and for changes in 

The group that developed this standard is currently considering developing a document that would addre

of tempprary overvoltages. 
Chapter headings: 

Introduction 

Interference sources, coupl.ing factors 

Grounding, earthing and screening 

Standards for interference immunity tests 

Supply system 

Protecting components against transients and surges 

Signal transmission . . . Field installation guidelines 

Apparatus design 

The design of interference-proof circuit boards . . . Communications 

Fvfi@:icn ... f'& 

ktIStigaGcE &S9Lrbmces . . . Tr3&!&=t;&g 

&n&sion 

Reviewer's annotations 

The emphasis of the book is on equipment design rather than power systems and installation practices. 

A limited scanning of the book and its index does not reveal the issue of cascade coordination as a topic. 
solution is proposed. 

REVIEWER'S ANNOTATIONS 

Test results show that an effective and safe 

combination of devices can be specified for full 

protection of the loads in the house. 

Thus, a coordinated protection scheme is 

feasible. The cost should be acceptab

yourself homeowners, although it m

deterrent to those owners who have to 

electrician to install a protector at the l

Based on increasing awareness in the te

regulatory agencies community of 

protection, the incorporation of protect

centers offers the best approach to new i

REVIEWER'S ANNOTATIONS 

The paper shows the effect of larze currents flowing in the neutrailgrounding cn~dllrtcx of the servi

building, and explores options for placing an arrester at the service entrance or at the end of branch 

both. 

The many oscillograms reproduced in the paper also show how a unidirectional stimulation (8120 ps cur

only in the grounding conductors) result in oscillatory transients in the differential mode. 

amount of current varies significantly for different 

sizes and ciesigns of transformers, ioads, and 

maE&ry. ='jIa. It is a:m hat he entire 

mcz&q c.acb.t & tiatd --.a&-- Jy JKUL 

M=cu_res &!m to protect &s t~rfamx genezi!!y 

increase the surge voltage stress on the load 

equipment. The source of the problem is the voltage 

drop along the secondary cable. Minimizing that 

voltage can effectively alleviate the problem at both 

the transformer and the load. These facts must be 

taken into consideration before developing 

transformer test standards to address the low-voltageside current surge problem. 

AUTHORS' CONCLUSIONS 

(Excerpts) 

Concerning proposed test levels for low-voltage 

current surges in distribution transformers, it wouid 

appr to be inappropriate to btpcify a single current 

=1?.&de far a!! tmsf~.me;s. TL,e aiiieit of siirge 

currpt_ && pzses !hrepd~ e- tpgsf~mer V%+* 

significantly with the design and k VA rating of the 

transformer. The current that flows is not a constant, 

but is determined, primarily, by the net differential 

mode voltage drop across the secondary cable and, 

also, by the impedances of the transformer, cable, 

load, and ground. 

Smaller-sized transformers with interlaced 

secondaries of low-voltage arresters will typically 

pass twice as much surge current as conventional, 

non-interlaced designs of the same rating. 

cable and between pole and house ground

25-Yv'A and 50-kVA non-interiaced transfo

dlow more current to fiow ihan the iO

kt&:!& tFafGmei L-~ of 

impedances. In fact, the impedance of 

transformer is relatively insignificant when 

to the cable impedance and the surge cur

transformer approaches the theoretical li

fact, in combination with different distribu

turns in larger kVA transformers may ex

researchers have reported that transforme

50-kVA or larger, are essentially immun

from low-voltage-side current surge p

Another factor might be that these transf

generally connected to more than one secon

which our studies indicate would de

voltages induced within the transformers. 

The system consisting of the distribution t

and ioad has a complex response to lightn

and very sensitive to changes in the charac

.L - I- -- --Iur: wmpunenrs of the system. Chan

*-"& -a- ..-A* L- *---- U-LOLUGI mu, - wA&id ~

considering the effects of the changes on 

the system. For example, protecting the t

insulation by interlacing the transformer s

or by applying low-voltage arres

approximately double the voltage stress o

for the smaller transformer sizes. The on

found that minimizes the problem in all a

system is to use shielded secondary cab

adequate mutual coupling between the n

phase conductors. This minigtizes the sur

by reducing the net differential voltage ind

lightning surge currents flowing in the cab
in controlling this stress. Interlacing the secondary 

windings will reduce the primary winding stress when 

the surge current is nearly balanced in the two 

secondary winding halves, but is ineffective when the 

surge current is not balanced. Either MOV or 

gapped arresters across the secondary terminals 

provide more complete protection for the 

transformer. Transformers with interlaced secondaries 

and those with low-voltage arresters can place greater 

stress on the load insulation. Arresters applied at the 

service entrance do not protect all insulation 

throughout the structure, but do not appear to worsen 

any insulation stress. Arresters applied at the 

transformer or at the service entrance should have 

about one-haif of the current surge capacity of >:-._ll...:-- -I--- A -L---l> L ---- - UI~L~~PUUUU GI= arrwren. -t:sren snuu~u nave a 

prGtm~v7e !eve! =f 2 k V far +Ae xF;& earace 

while A4 t V gpp~ &q~ute fcr t& tpaf~rm~r. 

would appear from the literature that MOV arreste

would be required for protecting loads. 

Arresters applied in the pole environment should ha

a current discharge capability of at least half of th

for a standard distribution class arrester. Arreste

applied at the service entrance should have the sam

capability because they see the same currents. T

minimum conduction level should be high enough 

coordinate with the primary arrester. 

Because the surge originates from a surge volta

drop in the service drop cable, clamping or limiti

the voltage at one end increases the voltage at t

other end. iiis impiies that the service entran

o-ug bt t" L& pr"Lp&&- t" cmrd&ate -w& 

t-"cFn-~- ..-t-+;n.. n;r nrrartar rhA..lA 

.'QYIIw.LY-. p"CL.CIIwY. *-a Q11-1-I aYwU'u 

cimilar in mtina tn the tmncfnrmer srr~cter and ha

--"Y.-. ... ----e .- -- *..-*--. -..---. -- ..

a discharge voltage of less than 2 k V to coordin

with load insulation. This arrester seems to be on

partly effective in protecting the house load if the

are other ground paths. However, the addition o

service entrance arrester is not likely to worsen sur

problems within the house such as might occur if t

transformer is protected without protecting any p

of the load circuit. 
circuits more frequently than believed. T

to be little that can be practically done to 

frequency of these surges. In fact, effort

to protect their own equipment may i

magnitude of the surges entering 

Therefore, load device protection that 

coordinated with other elements of the sy

prudent. 
surges can enter load circuits through utility system 

neutral paths. 

Surges may come from overhead and underground 

(UD) systems alike. The surges follow ground paths 

into the load, inducing high differential voltages as 

they pass through unshielded cables. Generally, both 

ends of the cables must be protected. Secondary 

arresters in the service drop environment may see as 

much as 113 to 112 of the utility's primary arrester 

discharge current. Arresters in the service entrance 

should have similar current discharge ratings as a 

secondary arrester on a distribution transformer. 

Service entrance arresters offer protection to load 

circuits that do not have other ground paths. 

Sensitive appliances and appiiances connected ro 

ciicci.s . . -*p& r,31~ple gruG pa& sbo-uid 5 av-e 

special protection. Arrester voltage discharge levels 

and current discharge capacities should be 

coordinated from the utility system all the way to 

load point. 

connection to the power supply. 

Surges can enter the load structure quite easily on 

system neutral conductors. Surge current 

conducted to the neutral nearly every time a util

primary distribution line is struck by lightnin

Because these lines are struck many times 

lightning-prone areas, surges may be entering lo

circuits more frequently than believed. There see

to be little that can be practically done to reduce 

frequency of these surges. In fact, efforts by utilit

to protect their own equipment may increase 

magnitude of the surges entering the lo

Therefore, load device protection that is carefu

coordinated with other elements of the system see

prudent. 
REVIEWER'S ANNOTATIONS 

Answers are provided to the following questions: 

What is the origin of the surges ? 

Are interlaced transformers immune to low-side surges ? 

Why protect both sides ? 

.-.. what do iow-side surge voitages iook iike ? 

Can a SN~ entrance arrester protect the entire house ? 
the system to the stroke current. The latter 

component is responsible for transformer failures 

while the former may be responsible for discharge 

spots often found around secondary bushings. 

Arresters at the service entrance are effective in 

diverting most of the energy from a lightning strike, 

but may not protect sensitive loads. Additional local 

protection is also needed. The tests affirmed 

previous simulations and uncovered additional 

phenomena as well. 

AUTHORS' CONCLUSIONS 

Low-side surges typically consist of two major 

components: a component ranging in frequency from 

0.8 to 3 MEz and a siowerchanging component that 

iepiaeE's :he h&ficiivespns of &e sjisiem b he 

rate of change of the lightning stroke current in the 

triplex cable. The tests confirmed earlier analyses of 

low-side surge phenomena in transformers and 

verified that the phenomena affecting the transformer 

can be analyzed by simply considering the 

inductances in the secondary system, neglecting the 

cable capacitances. 

low-side surge failure should be protected w

arresters in accordance with previous analyses. 

The service entrance arrester in all ratings studi

(175V to 650V) appears to be quite effective 

protecting conventional insulation against the low

frequency component of low-side surges. Howev

it should not be relied upon to protect the entire lo

circuit, especially sensitive loads, against the high

frequency component of the surges. The appropri

local protection of devices sensitive to that type 

surge is still required even if there is an arrester 

the service entrance. It would appear that m

practical lengths of secondary circuit feeder cab

would be sufficient to force most of the energy fro

a low-side surge through the service entrance arres

and, thus, heip prevent ihe faiiure of the io

protective device. Che area &at remains open 

investigation is the effect of the turnoff transient 

MOV-type arresters in load circuits on t

transformer. Another is the switching surge a

power frequency coordination of arresters in 

secondary circuit. 
protection coordination to both utilities and end users. 

An effective MOV protection coordination scheme is 

also described and recommended. 

close to the load or equipment as po

arrester can guarantee the protection o

device. 

In most distribution systems, transforme

circuit protection is rarely used and whe

often miscoordinated. Many 175 an

arresters do not have the current carryin

to survive the 34 kA surges that can be 

transformer secondaries and service entr

volt arresters can also miscoordinate with 

primary arrester SSPLs. 650 volt ar

coordinate, but may provide inadequ

protection. Both current and voltage coor

be improved by a 480 volt arrester wi

rating. Properiy coordinated protection u

.-.A 1 

VVIL nigh current arrester shouid becom

,,,*:,, 6, -.....-. L-6%- p,,,,,, , PI"-L vuu ihe iiiitliQ'~ 

tr2&p-es md eEd ~r's la&,.

REVIEWER'S ANNOTATIONS 

Same conclusions as Man & Mendis, 1992 
g p

of various load systems. 

REVIEWER'S ANNOTATIONS 

A comprehensive report on the recording of disturbances at various computer sites. 

THe detailed tables include statistics on several categories of disturbances. Most significant to the present con

are the temporary overvoitages, with a classification bin of overvoitages above 35 9% of the nominai rms iine voita

A few occurrences of these are reported in some iocations. 
that travel backwards into the mains from 

struck by lightning. 

REVIEWER'S ANNOTATIONS 

Cites 10l350 ps as a waveform to consider for simulation of near-by and direct stroke, in addition to t

waveform, which is considered appropriate for distant strokes. 

Proposes to provide at the service entrance a two-stage surge arrester consisting of a gap on the utility 

varistor on the load side, separated by a coordinating inductance. Clearing of power-follow in the 

discussed. 
approach to coordination. 

Examples are given, with schematics and device photographs, of the application of arresters in low-voltage TN a

TT networks. 
Furthermore, it is found that in an insta

two or more surge protective devices, 

energy stresses will generally occur on 

with the lowest clamping voltage. The

protection level for the secondary protec

be selected somewhat higher than for t

protection independent of the location. 

the current flowing in the secondary dev

lower than in the primary ones, and 

protection is obtained for sensitive 

aithough the nominai ciamping voitage i

L: -L up. 
This contribution has appeared in several IEC documents, SC28A, TC64, and now SC37A. 



(

diodes). When a system includes both types of surge 

suppressors, it is necessary to take into consideration 

the impinging surge voltage as well as the 

corresponding available surge current. 

REVIEWER'S ANNOTATIONS 

ppg 

the impulse withstand voltage of 

equipment. 

It is possible within a system to cascade a number 

interface surge suppressors to achieve the vario

overvoltage categories. The number of overvolta

categories will be determined by the number 

different surge suppressor residual voltages specifi

However, it is also possible to achieve the low

overvoltage category by the use of a suitably selec

qp iesmi zt 'he 6r;gh of the -~s*a:;ation* 

Note the continuation of the expectation that a cascade is possible, but the emergence of the idea that the low

clamping voltage might be obtained by a service entrance arrester. 

pp

contributing to shared information on the subject. 

REVIEWER'S ANNOTATIONS 

This paper is only a status report on an ongoing project aimed at characterizing the aging, if any, of generic MO

under the effect of repeated swell over the service life of a varistor. 

Two mechanisms have been encountered in the test series: a relatively small (less than 3 5%) change in varis

nominal voltage for limited cumulative stresses, and a failure by overheating when exposed to stresses of excessiv

longduration (seconds) temporary overvoltages. 

A more comprehensive paper should be presented at a future meeting. 
iai, J. S . and Martzloff, F.D. - Coordinating Cascaded Surge-Protective Devices. Pro

IEEE/US Annual Meeting, October 199 1. 

AUTHORS' ABSTRACT 

Cascading surge protection devices located at the 

service entrance of a building and near the sensitive 

equipment is intended to ensure that each device 

shares the surge stress in a optimum manner to 

achieve reliable protection of equipment against 

surges impinging from the utility supply. However, 

depending upon the relative clamping voltages of the 

two device& their separation distance, and the 

waveform of the impinging surges, the coordination 

may or may not be effective. The paper provides 

computations with experimental verification of the 

energy deposited in the devices for a matrix of 

combinations of these three parameters. Results 

show coordination to be effective for some 

combinations, and ineffective for some others, a 

finding that should reconcile contradictory 

conclusions reported by different authors making 

different assumptions. From these results, improved 

coordination can be developed by application 

standards writers and system designers. 

AUTHORS' CONCLUSIONS 

1. Coordination of cascaded devi

achieved under various comb

parameters, but some combin

result in having a suppressor 

energy-handling capability call

divert the largest part of the su

This uncoordinated situation 

adverse side effects when hi

surges occur. 

Significant parameters in 

successful coordination involve th

over which the occupant of the p

no control: the relative clamping 

the two devices, their separatio

and the prevailing waveforms fo

surges. This uncontrolled situat

a challenge and obligation for 

writing groups to address the p

develop consensus on a tr

advantages and disadvantages o

versus Low-High. 

3. Coordinated schemes can be p

utilities to their customers, i

service entrance arrester and o

plug-in devices to be install

dedicated protection of sensitive 

However, even such an 

coordinated arrangement could 

by the addition of a suppressor 

low clamping voltage, not an i

likelihood in view of the present 

for lower clamping voltages. 

REVIEWER'S ANNOTATIONS 

The paper describes 72 combinations of 130 V, 150 V, and 250 V devices arranged in cascades, wit

distances ranging from 5 to 40 meters, and with 8120 ps and 1011000 ps impinging waveforms. 

While the 8/20 ps waveform can still result in a contribution from both devices to sharing the surge 

1011000 ps waveform does not produce any inductive separation of the devices past the rise time, so 

is equally shared between devices of equal rating, and for two different devices, the lowest rated take 9

of the total energy. 

Cascade Bibliography - September 1992 
and distance between the devices but not effective for 

other cases. To develop the performance criteria for 

cascaded devices, all possible environments need to 

be taken into account. This paper uses the voltage 

clamping level of cascaded devices, their separation 

distance, and the surge waveform as parameters to 

study the energy deposited in the devices. All 

assumed cases were studied using computer 

simulation with necessary experimental verification. 

Results show reasonable agreement between 

simulation and experiment. A total of 72 case study 

results provide standards writers and application 

engineers with quantification information for the 

development of improved cascade coordination. 

REVIEWER'S ANNOTATIONS 

probability and severity of losing neutral, su

energy from switch-mode power convers

equipment; size of conductors, and the dista

between the surze-protection devices. 

Although the MOV model described in this pa

successfully predicts the I-V characteristics and su

responses, especially the energy sharing of cascad

devices, more analytical studies are needed to redu

the deviation between simulation and experime

These include: 

MOV stray inductance and capacitance 

more accurate waveshape matching 

necessary. 

Consensus of MOV characteristics for 

same voltage level and size of the device 

different manufacturers 

Modeling of a gap-type surge protect

devices which would cause different su

responses when used as the arrester 

replace MOVs. 

Well-defined impinging surge sour

including voltage and current waveforms a

the coupled source impedance network. 

This paper contains a detailed report on the measurements and computations that were the basis for the two pap

[Lai & Martzloff, 19911 and [Martzloff & Lai, 19911. 
ggg 

frequency, and also in terms of the overall impact of 

such changes on the calculated overvoltage level. 

Recommendations are provided for the use of these 

methods under different sets of system conditions. 

p

conservative only for well grounde

Overvoltages on systems where the 

parameters depart significantly from t

values should be calculated using th

recommended in this paper. In many ca

of ratings to be used on such system

required. 

Based on a comprehensive evaluation 

methods for calculation of overv

multigrounded distribution systems, i

concluded that the commonly used meth

symmetrical components is inadequate f

but the simplest calculation for a system 

ideal grounding parameters. 

For systems where poor grounding co

known to prevail, the best method of a

neglect the ground effects altogether. 

The best overall results are provi

sophisticated, matrix algebra bases me

analyzes the ladder network cell

multigrounded distribution neutral indivi
Communications and Power, pp 451

454. (In French; English translation available from FD Martzlo

Coordination of overvoltage protection in low-voltage residential systems) 

AUTHORS' ABSTRACT 

The development of metal-oxide varistors has made 

possible a substantial improvement in the mitigation 

of overvoltages in residential, commercial or light 

industrial power systems. For instance, transient 

suppressors are now available that can be plugged 

ink a wd! fnaptx!=, t&1~ -6" pssib!e the 

pmtpft;~n ~f zp.~?p!ia~s ac =!=&&c &J~W that . . mioht & &mgpj by ~v=mdtag=s mcurzg m -a" 

nnwer cvct~mc y- -- -- -J "--. 

However, due to economic considerations, these 

suppressors have only a limited capability for 

absorbing high current surges that may be associated 

with lightning strikes occurring nearby. Thus, one 

may ask whether the installation of a suppressor with 

limited capability might not pose a risk of failure or 

create a false sense of security. 

It is then worthwhile to examine what occurs in a 

building provided with suppressors having different 

capability, located at different points of the building. 

as a function of the surge current intensity imposed 

by the lightning strike. Furthermore, the combination 

of several suppressors may allow a coordinated 

p+&=.ti~= fer r&&!f: QF~&=, WE& it wcu!d 

worthwhile to demonstrate; 

AUTHORS' CONCLUSIONS 

1. It is sufficient to inject, in the ground conductor 

of the service drop, a surge current corresponding to 

a moderate lightning stroke to reach hazardous 

voltages between the phase and neutral conductors 

within the building. 

2. Commercially available protective devices a

capable of limiting overvoltages to acceptable limi

even in the case of an injection corresponding 

extreme values, several arrangements may 

considered: 

b) A metal-oxide varistor, presen

available only as an industrial component packag

correctly installed in the service panel (sh

connections) would be sufficient to limit overvoltag

for all the building, even for high amplitude lightni

strokes. 

c) A varistor with limited capability, t

VSP-1, installed at a particular receptacle, will lim

overvoltages at that point to values that are acceptab

for electronic devices, without being itself exposed 

hazardous stress, if its distance from a panel - n

equipped with protection - is greater than about 

meters. For shorter distances, the stress applied 

the VSP-1 might exceed the expected reliability, w

failure of the varistor. This failure would s

provide protection during the surge, but lead to a tr

of the panel breaker. Of course, if a protecti

according to (b) were provided, it would not 

necessary to install a VSP-1. If the protecti

provided at the service panel is less than ideal (HLP

the addition of a VSP-1 at the receptacles that supp

sensitive devices would provide protection for the

devices, while the HLP would provide diversion 

high currents. 

REVIEWER'S ANNOTATIONS 

The conclusion presented in this paper, that coordination can be achieved, is based upon two premises: 

1. The impinging surge (into the ground systemi mt in phxw c~dmt~n) is ca@d bt_n & &&

conductors of the service drop and appears as a L-N mode at the service entrance, hat still with a sh

rise time. 

2. The service entrance is a gap-varistor combination, so that as soon as the gap has sparked-over (during t

ascending front of the wave), all current ks transferred to the arrester, away from the suppressor at the e

of the branch circuit. 
AUTHORS ABSTRACT 

Surge protectors can be installed in low-voltage ac 

power systems to limit overvoltages imposed on 

sensitive loads. Available devices offer a range of 

voltageclamping levels and energy-handling 

capability, with the usual economic trade-off 

limitations. Coordination is possible between lowclamping-voltage devices having limited energy c2pgbihty md &g~=&q~g~vG~+~ge bevim hzvhg 

hiah energy q&i!iv. pue ppr -e 

aaqie~ af r_mr&&i~n, .r &!i~~xl 

experimental resu!& on surge prqxgatinn. 

AUTHORS CONCLUSIONS 

Coordination of surge protectors is fe

existing devices, even if device character

The experiments reported in the paper 

facts from which conclusions can be draw

Fact 1: Where an unidirectional current 

into the ground system only, the 

the system is an osciiiating voir

1 TT- C-- --.---- -A wr US syswm d~~i'd

Fzcc 2: pue qGpvra!sGt mcic- iz

determined by loading the system

range of 50 to 100 Cl for the 

system investigated. 

Fact 3: Without substantial connected lo

system, the opencircuit surges a

the service entrance propagate 

branch circuits with very little at

Con. 4: Coordination of surge suppresso

a finite impedance to separat

devices, enabling the lower voltag

perform its voltageclamping fun

the higher voltage device pe

energy-diveriing hction. 

Con. 6: Indiscriminateapplication of surg

may, at best, fail to provide th

protection and, at worst, cause 

operation of the suppressors. 

needed is a coordinated approac

the recognition of the essent

governing devices and surge pro

, 

A ,.fi..A,?.-.-,?.A ..a-.+.- wuuu,- aiib arclik: piiXiatioii of ihe idvmtion initiaiiy deveioped in the propri

declassified) 1978 Crouch & Martzloff report. 
low inherent immunity must be balanced against the 

risk of premature aging of the protective device. 

Lower clamping voltage causes more frequent hteFJeE~3x =f +Ae prc;+e-ive &vice, =-Iera:@ pe 

rroino 7h~ pgpr fegr p=sib!e =f -*-a- *-- 

wh nremah~r~ r--I----- gghg, -!!kg for I mere r&ref51! md 

thus more reliable app!imtion of protpr-the devices. 

AUTHORS' CONCLUSIONS 

Several mechanisms involving surges or momentary 

overvoltages can cause accelerated, or premature 

aging of varistors, if the clamping voltage is selected 

at too low a level without appropriate consideration 

of all factors. 

A second mechanism, fortunately not occurring too 

frequently, involves fuse blowing and can produce 

immediate destruction of the varistor at the first 

occurrence if the clamping level is selected at too low 

a level. The implications of this situation needs 

greater recognition among varistor users. 

recognized by high-voltage arrester designers, but n

by low-voltage electronic circuit designers. 

The obvious, but difficult remedy to this situation 

to design equipment with a reasonably high surg

withstand capability so that retrofit using protectiv

devices with very low clamping voltage will not b

necessary. For those situations where a clo

protection would be required, a very caref

consideration of all factors becomes imperativ

rather than cookbook application of protectiv

devices. 

In the &seiice of a demaiidirig retrofit chaiieng

+La-- :- ..- ,.A.,.-&--.-. .-.-A ----:A--Ll- ---I&-. 

LUG~~ 1- uu aovamap auu 2 WUSIUGI~UIG pualry 

n*nr,;A;"n a *- .n trrr.. r .crr+-+:rr. ,r--:- L

yrvw~o-5 cvv ~la~~un y~ub~+nuu uual~u~ U

_y-jfjlhg n&less!y !Q\Z, c!aq@ Such 

voltages are counterproductive to total syste

reliability. Thoughtful design can provide goo

performance with good reliability; short-ter

perspective and quick fixes can only compromi

long-term reliability. 

REVIEWER'S ANNOTATIONS 

The title is the theme. 
AUTHOR'S CONCLUSIONS 

1) The response of the step down transformer and its 

associated bus wiring to stimulation by a 1.2150-ps 

unidirectional surge contains two components: 

a unidirectional component matching the 

stimulation, and 

a ringing overshoot at a frequency dependent upon 

the circuit characteristics. 

2) m-e uA&re&nd surge ~~q!=r thr~pgh +&e 

transformer according to the tu-ns ratin, with 

negligible attenuation. The ringins nvershmt 

frequency depends on the circuit parameters; its peak 

can exceed twice the peak of the stimulus. 

initial peak of the surge arriving at the rec

Subsequent parts of the surges, howeve

affected. 

6) Providing protection against power lin

the power line interface of devices linked 

communication circuit does not guarantee 

occurring in the power line environme

cause damage to the devices. A more com

,,. ':,- "^l.,-- ^^^ .l:--r:- L-.L .t 

~LULCWLUU JC.LIGUG, LUU~UIIIPLUI~ WLU UI

md the &a bhe, is rq$,& te ecgGie Fia
3. Coordinated schemes can be proposed by utilit

to their customers, including a service entran

arrester and one or more plug-in devices to 

installed for the dedicated protection of sensit

appliances. However, even such an engineer

coordinated arrangement could be defeated by 

->a:.:-- -c - --.:.L - 1 ---. -I---:-- ;IULUILIUU UI a aupprwwx wlul a wry IUW sraiupl

..A~+~,.P -A+ ;rn:-:Gnnr+ l:tP1;hrrrrrl ;- .r;a..r -4 

vu~wp, UUL au samts~lttw~ ttn=tu- u VLG- UL 

pmat mmpd?icE fcr C!sFapi3g -gC!tages. 
TABLE 1 

MEASURED CURRENTS AND VOLTAGES, CALCULATED IMPEDANCE (10 m CABL

FOR THREE WIRE SIZES AND THREE WAVEFORMS 

II waveform I I I 

11 Peak current, Ip (A) 100 I 170 1 120 

Nominal generator 1 011 000 ps 

Actual rise time of current 0.8 22 2 5 

(psi 

*Wire size (AWG) 

Effective impedance V,/Ip 8.0 7.9 8.0 4.5 4.6 4.7 0.8 0.8 

cn) J 

Ring Wave Combination Wave 

REVIEWER'S ANNOTATIONS 

Data for evaluating the effect of the inductance in separating two devices, as a function of waveform (m

and wire size (minor effect). 
1. The reality of having many millions of 130- 

V rated varistors installed on 120-V 

systems, and 250-V rated varistors installed 

on 230-V systems makes the ideal scenario 

of a wellcoordinated cascade difficult or 

perhaps unattainable in the near future. 

2. As a compromise, a cascade with equal 

voltage ratings for the arrester and the 

suppressor can offer successful coordination, 

if the impinging surges are presumed to be 

reiaiiveiy short. 

cascade would be lifted. 

6. The idea of an expendable, one-shot arrest

at the service entrance could offer a soluti

out of the dilemma and should be furth

investigated. 
y gp

service entrance, these surges can penetrate further 

into the customer's system. Damage caused by lowsid~ surges can 'be avoided if properiy coordinated 

arresters are installed at the transformer secondary, 

service entrance, and load device. 

This paper describes the secondary surge phenomena 

and the importance of protecting the service entrance 

and critical load devices properly, especially when 

secondary arresters are applied on distribution 

transformers. A properly coordinated and effective 

MOV protection scheme is described and 

recommended. 

g gqp

(2) place the arresters as close to t

equipment as possible. No arrester can g

protection of a remote device. 

In most distribution systems, transforme

circuit protection is rarely used and whe

often miscoordiiated. Many 175 an

arresters do not have the current carryin

to survive the 33 kA surges that can be 

transformer secondaries and service entr

volt arresters can also miscoordinate with 

primary arresters SSPLs. 650 volt ar

coordinate, but may provide inadequ

protection, Both current and voltage coor

be improved by a 480 volt arrester wi

rating. Properly coordinated protection u

volt class arrester should become standar

pieiwi both distribution transformer

,L..;c.- 

YVIIUW. 

REVIEWER'S ANNOTATIONS 

Note the recommendation of a 480-V arrester at the service entrance. This recommendation proceeds fro

about the current coordination of the arrester. 

However, the coordination of energy sharing between service entrance and internal suppressor does no

addressed. 

A table shows current values in the range of 2 to 17 kA for 'Load Arrester' but this reviewer could 

definition of the what this load arrester is -- is it a SPD at the end of a branch circuit ? Are we talking 

flowing in the branch circuits wiring ? 




-- Siruica, V. - EM1 Control in Low-Voltage Power Installations. Proceedings, 1987 EMC Ziiri

Symposium, pp 429-434. 

AUTHOR'S ABSTRACT 

(Excerpts from 'Introduction') 

According to Martzloff [3] the impedance of low 

voltage power installations in general is in the range 

of 50 to 100 Q, therefore, the expected minimum 

current through the secondary suppressor must be in 

the range of 10 to 40 A until the gap of the primary 

surge arrester will be able to break down. It would 

therefore be of advantage, if the surge impedance of 

the installation circuit is not too low. Our measurements of impedances in low voltage power installations in different structures have shown, that the 

impedance may decrease by a factor of up to three by 

moving from a distant point in the instaiiation to the 

main power distribution box of the structure. 

Approaches have been made to artificially increase 

the impedance of low voltage power circuits by 

applying femte cores in coils of power network 

filters. It is unfortunately often forgotten that core 

saturation currents for the core dimensions normally 

used usually are very low, much lower than usual 

surge currents in the line. The most safe way in 

increasing the impedance of the particular installation 

line segment is to separate the surge suppressors by 

a properly designed physical line or a noise 

suppression transformer. 

=f ktemticm! r@a:iom sd 

r~ornrnenrtati~~c reding the =pp!iat:~n sf ~~rge 

suppression in particular in industrial power !"".s Ilnn 

installations and the need of standardized equipment 

testing procedures and test-level specifications have 

been recognized. An overview of the situation of 

today has been given in a paper by Martzloff [8]. 

In the following we shall present and discuss our 

experimental and theoretical investigations made on 

an artificial low voltage power installation segment 

and on ordinary low voltage power installations in 

different structures. The investigations have been 

performed in order to determine the values of the 

basic electric circuit parameters and to deduce the 

electro-physical relationship for different components 

and circuit parameters of a modem low voltage 

power installation. 

AUTHOR'S CONCLUSIONS 

(Excerpts) 

Spark gaps should only be used as overlo

protectors of varistors, or as insulation-coordinat

protectors where AC-short circuit follow currents 

not to be expected. In a 380V AC power system 

varistor V' - type should be installed in the m

power distribution box in accordance with 

established practice. In general, if there are 

special reasons, additional varistors of type VL are 

necessary to be installed in subdistribution box

Further more, varistors of type V' in 

subdistribution boxes would draw high surge curre

along the connection lines between the boxes. T

could be a disadvantage from the point of interfere

suppression. The secondary varistors V2 should 

installed near the sensitive equipment. Preferab

such equipment should not be connected to the pow

line near the main distribution box. A lo

installation line may be of advantage. 

A reasonable value of the nominal voltage fo

secondary varistor of V2 - type is between 620 a

750 V DC and the diameter between 14 and 24 m

Refening to the Table 4, only a minor part of 

total surge current will pass through the installat

line and the varistor V. An optimized protection 

the equipment, regarding the common mode and 

be-"-.- ---I- ---I .--- 6'-Y GE%? uuuc vuiwge surges, is vbttined by us

a set ef +h-ee vaisto;s 181. 

The surge valbge rrrress fie v&st~r V2 & 

appreciable longer rise time than the original surg

varistor V'. For an injected lightning current of 1

us, the dominant frequency of the voltage su

across V2 will be in the range of 10 kHz. T

makes it possible using an additional pow

transformer, e.g., an isolation transformer, wh

significantly reduce the surge entering into 

protected equipment. We may also conclude t

equipment with a power transformer is very suita

to be efficiently protected using a set of second

varistors. 

REVIEWER'S ANNOTATIONS 

Paper reports computations with EMTP and makes reference to measurements, presumably reported in Scuka, 1

for a cascade of two varistors. 

The impinging surge is a current of 1/50 ps waveform - a steep front. 

Paper seems to encourage varistor at end of branch circuit to have bgher voltage rating than varistor at serv

entrance. 

Cascade Bibliography - September 1992 
reliability has recently become very important to both 

the utility company and the consumer. We subjected 

a total of 16 different clocks, television receivers, 

microwave ovens, and dc power supplies to three 

different transient overvoltage (surge) waveforms 

with a~plih~d-e k.huem 05 and 6 kV. All of these 

devices were operating from the ac supply mains 

when the overvoltage was applied. The switching 

power supplies and television receivers were damaged 

with surges between 4 and 6 kV. Three of five 

vulnerable to damage by surges wi

circuit voltages between 4 and 6 

protection is desirable for thes

appliances. However, some of the app

project were not vulnerable to damag

number of surges. Further researc

archival papers, is recommended on 

effects of surges on appliances and (2

mitigate damage and upset by surges. 

models if digital clocks were upset (temporary 

malfunction) with surges between 1.6 and 6 kV. 

REVIEWER'S ANNOTATIONS 

Two noteworthy paragraphs in the discussion presented by the authors read: 

The results of this research show that the conventional wisdom that electronic 

appliances are easily damaged by surges with a peak voltage of a few kilovolts 

may greatly exaggerate the effect of surges on modem consumer appliances. 

If manufacturers include metal oxide varistors inside appliances in order to 

prevent damage or upset, they should consider using varistors rated for twice the 

normal nns voitage. iiis reiativeiy iarge conduction voiiage wiii make ii 

possibie to instaii a secondary arresters iipsirearn from the zpiijphice th: $is 

g- cmr&8i~oii -=fi .he var;$..os 'Ae .&PP~;~M. 

The conclusions and discussion remarks point out that the quest for very low protective voltage, su

400 V may indeed be an exaggeration of the need for protection. The immunity to surges as high a

in the paper may be the result of inherent immunity of the power port circuitry, or the result of 

protection at the input. In either case, the authors have provided significant evidence that relatively 

levels at the point of load connection, a requirement for a successful cascade, should not be viewed 

the appliances. 

Another anecdotal consideration is that the highest percentage of reported failures (50%) cited in the 

TV receivers and VCRs. The authors suggest that this finding may be related to the high cost of th

more likely to be reported than the failure of a clock. This reviewer suggests that a possible contribu

percentage may be that TV equipment is a two-port system (power port and communications port), 

single-port clock, raising the issue of the need for special protection of two-port devices. (In the te

the authors, only differential-mode surges were applied to the two-conductor line cord, no mention 

ad rpfprp~cp, VO!~~P. ~f &e signal pa;) 
. . . In most hybrid protection circuits, shunt devices with smaller clamping voltages are installed downstream, nea

the equipment to be protected. Some series impedance is installed between each pair of shunt protective devi

to provide proper coordination. . . . 

... But for overvoltages with durations of a few milliseconds, it will be difficult to insert an adequate ser

impedance between shunt protective devices and still maintain normal operation of the load. . . . 

.. . One solution to the problem of coordinating multiple varistors on the mains is to reverse the normal order 

devices. Place the varistor with the smallest value of V, at the secondary arrester. Varistors downstream wo

hzge s;ighi;y krger v&iies of '"T,. ( n-ame iai ex-p ie foiiowsj 
Measurements as well as computations are reported for several combinations of service entrance arresters 

150 V) and branch circuit end suppressors (130, 150, 250 V). 

The concIusion that good coordination can be achieved with lower voltage clamping at the service entra

founded but does not take into consideration the reality of uncontrolled low levels of clamping from 

installed TVSSs and built-is sgpprescn.rr,. 
limits. 
voltages. Best load protection was achieved with 

movs in all three locations. Distribution of surge 

current between movs in three locations is shown to 

be good for both low and high surge currents. 

Coordination of protective levels was shown to be 

achieved, even with long surges typical of lightning. 

Testing with the new A

Category C3 combination wav

in reasonable agreement with t

from more realistic light

However, the energy deposite

this wave is much lower than 

lightning. 
ppyg

suppressors show that many can be set on fire in a 

reproducible way. It is concluded that internal 

protection against overheating is required to ensure 

suppressor safety and that safety agency approvals 

should include fire hazard tests. 

y , 

suppressors to overheat internally. 

Products equipped with overcurrent fuses or magne

circuit breakers may catch fire in rare cases. Thi

true for those having both plastic and metal housi

and components rated for both 130 V and 150 V. 

A fire hazard test, similar to that described in t

paper, is proposed to be added to safety agency te

for surge suppressors and similar products.