A New Concept in Arrester Design 

R.C. Sakshaug, J.S. Kresge, and S.A. Miske 

General Electric Company 

Reprint, with special permission, of IEEE Transactions PAS-96, no.2, March/April 1977 

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Significance: 

Part 7 Annex: Mitigation Techniques 

This paper was approved for presentation at the 1976 PES Summer Meeting to announce the availability 

of zinc oxide varistor material for high-voltage arresters. It is significant that this announcement occurred 

in 1976, four years after the 1972 trade-press announcement of the low-voltage version of zinc oxide 

varistors under the trade name of GE-MOV (see MOV Announce and Superalpha in this Part 7), and this 

only after undertaking the research described in this seminal paper. 

While technically outside of the scope of the Anthology which is focused on low-voltage SPDs, this 

seminal paper is included as an Annex to the public-domain SPD Anthology to provide perspective on the 

extent of the research to which the new material was subjected before launching a commercial product. 
IEEE Transactions on Power Ap~aratus and Systems, Vo!. PAS-%, no. 2, ~archjApri1 1977 

A NEW CONCEPT IN STATION ARREmR DESIGN 

General Electric Company 

Plttsfield, MsssPehwtts 

ABSTRACT 

In 1968 Matsushita Electric Industrial Co. of Osaka, Japan announced a 

new improved non-linear resistance material based on zinc oxide. The 

original devices were small low voltage units applicable for use in the 

electronics industry. In 1970 work was performed by the General Electric 

Co., and is continuing, using its own funds and technical resources, to 

develop larger devices for use as a substitute for silicon carbide valve blocks 

in surge arresters. Development has now progressed to the point where this 

material, with non-linearity characteristics far superior to silicon carbide, 

canbe used to manufacture station type arresters whichdo not employ series 

gaps. The purpose of this paper is to outline some of the characteristics made 

possible by the new material which is becoming increasingly important to the 

electrical industry. 

INTRODUCTION 

It has always been understood that the optimum arrester characteristic 

would be one in which the arrester would: 1) enter into conduction at some 

voltage above arrester rating, 2) hold that voltage with little change for the 

duration of the overvoltage surge, and 3) substantially cease conduction at 

very nearly the same voltage at which conduction started. Such an arrester 

would conduct oqly that current required to reduce the surge voltage to the 

arrester protective level. Any arrester holdinga lower levelof voltage during 

all or part of the conduction period must conduct more current and absorb 

more energy. 

Each major development in the evolution of arrester technology has been 

a step toward the optimum arrester characteristic. The first arresters were 

simple spark gaps capable of supporting essentially no voltage during conduction, and as a result, the arresters were generally incapable of clearing 

Power fiwluency follow current after sparkover. An improvement was made 

by adding series resistors. A very substantial improvement was obtainedby 

the development of non-hear resistors to allow the arrester to support as 

much voltage as possible during the flow of power 6equency follow current 

while maintaining reasonably low protective levels. The most recent improvement has been the development of current Smiting gaps. Cument 

limiting gaps used in series with non linear resistors made it feasible to 

further reduce protective levels for surge currents while maintaining a more 

constant voltage during the flow of arrester current. Fig. 1 illustrates the 

maximum volt&es pr&cedacross acurrent limiting gap arrester at various 

Cment levels. It will be noted that. by desian, the voltage produced by the 

current limiting gap is the amount kqkred to obtain a totalarrester voltage 

as Imras possible to aconstant value equal to the switching surge sparkover 

of the arrester. Because the arrester voltage is kept as high as it can be 

without exceeding switching surge protective level, the magnitude and in 

many cases the duration of current drawn by the arrester is minimized.' As a 

msult, the energy that must be dissipated is reduced. Another method for 

visualizing the situation is to note that in Fig. 1 at a current of even 500 

aWw2.s the resistance of an arrester rated 258 kV, for instance, is: 

13,000 volts 

500 amps 2r$ = 11 18 ohms 

For a surge impedance of 350 ohms, the arrester resistance exceeds the 

90- impedance of the surge. It is well known that maximum power is 

h8ferre.d to a load when the load and source resistance are equal and 

decnases as the load resistance becomes higher than the source resistance. - 

- 

p 76 393-9. A paper re-d and appmved by 

Surge Protective Devices Cunnittee of the 

fEEE Pwer Engineering Society for presentation at 

EEE PES Swp-ner Pketing, Partland, OR, July 18- 

23, 1976. ManusCri~t submitted March 1. 1976; made 

S. A. Mkke, Jr. 

General Ektric Company 

Scbenectady, New York 

The development of current limiting gap arresters was in considerable 

measure responsible for a number of improvements in arrester performance 

including: 

1. Reduction in liitning discharge voltages made possible by reducing 

valve element resistance; 

2. Reductions in arrester size because of the reduction in energy absorbed 

fora given surge level and because of energy sharing between gaps and valve 

elements; 

3. A reduction in protective levels on HV and EHV systems in particular 

because of the overvoltage reseal capability of current-limiting gap arresters. 

Current limitinggap arresters have been widely applied with an excellent 

service record; however, they do possess certain inherent limitations most 

of which are related to the fact that the arrester voltage is not at the level 

shown by Fig. 1 during the whole arrester operation. Instead, the arrester 

voltage falls to the valve element voltage immediately after sparkover, and 

does not rise to the level shown in Fig. 1 in less than a few hundred 

microseconds after sparkover. (')Until gap voltage is developed, the arrester 

current is given by: 

E surge - V valve element 

I arrester = Surge Impedance 

When the circuit in which the arrester is operating has low surge impedance (multiple lines, capacitor banks, or cable circuits), the initial arrester 

current can become very high. It is possible in some cases of very low surge 

impedance for the initial current to be so high that it does not move away 

from the point of initial arc strike into the normal arcclearing region of the 

gap units. As a result the arrester may fail to clear, or the erosion of the 

electrodes may be sufficiently severe to cause a change in arrester 

sparkover.' A simi problem may arise during operation of current limiting 

fuses because of the abiiity of such fuses to switch high fault currents very 

rapidly into arresters of low rating compared to fuse rating.' 

' 0 100250 500 750 1000 1250 1500 1750 2000 

AMPERES CREST AT MEASURED VOLTAGE 

Fig. 1. Maximum voltage vs. current for a6 kV section of a modem current 

Smiting arrester design. 

rn 

t; 

P 

S 

E 

AMPERES 

Fig. 2 Volt-ampere characteristic of 6 kV valve elements. A = zinc 

oxide B = silicon carbide 
AMPS/~~~ 

Fig. 3 Normalized volt-ampere characteristic of zinc oxide and silicon carbide valve elements. 

It has long been recognized that it would be advantageous to be able to 

design an arrester without the use of series gaps because: 

1. Gaps are subject to change in sparkover ifan arrester is not adequately 

sealed; 

2. Overvoltage applications may be limited by the probability of sparkover 

resulting from surface contamination; 

3. The number of parts used in gaps is large compared to the number of 

parts used in the whole arrester, and the probability of misassembly or part 

failure usually increases with the number of parts used. 

Curve A of Fig. 2 is a voltagecurrent plot of the new zinc oxide based 

valve element material. The new valve element has a characteristic so 

non-linear that the voltage is nearly constant for a wide range of currents. As 

a result, an arrester designed using these valve elements, and without series 

gaps, more closely approximates an ideal constant voltage device than is 

possible using the most modem current limiting gaps in series with silicon 

carbide valve disks having voltage-current characteristics as illustrated in 

Curve B of Fig. 2. The new arrester draws very little current until a voltage 

approaching the protective level is reached, and then only that current is 

drawn which is necessary to limit the overvoltage to the protective level. As 

a result, the arrester absorbsothe minimum amount of energy required to 

provide protection at a given voltage level. 

Curve A of Fig. 2 has been replotted (on a normalized basis) in Fig. 3 with 

an extension to much lower currents than for Fig. 2 and with the voltage 

scale expanded for improved resolution. From Fig. 3 it can be seen that for a 

change h current ove; a total range of 5 decades from 10.' to lW3 ampslcmz 

the voltage increase is only 56%. With such a highdegree of non-linearity it is 

entirely feasible to use these elements without series gaps in an arrester 

havingadicharge voltage at 10 kAequa1 to that for present designs. For such 

an arrester the current at operating voltage is only about 1 milliampere which 

is the same order as the grading current of existing designs. In fact, the watts 

loss at operating voltage for such a design is only about 0.15 watts per kV of 

rating or two-thirds of that for an existing design. 

VALVE ELEMENT CHARACTERISTICS 

The valve element consists primarily of zinc oxide, but it contains small 

amounts of other selected metal oxide additives, which serve to produce the 

desired highly non-linear resistive characteristic of the material. The fmely 

cmshed zinc oxide and additives are prepared as a thoroughly mixed flowable aowder which can be pressed into disks of the desired size. When the 

pressed disks are sintered at a high temperature a dense polycrystalline 

ceramic material results. The basic structure of the sintered body is a matrix 

of highly conducting zinc oxide grains sumunded and separated by highly 

resistive intergranular layers consisting primarily of the metal oxide additives. Under suRicient electrical stress the intergranular layers start to 

conduct, with the conduction characteristic being highly non-lmear as illustrated in Fig. 3. The specific characteristics shown in Fig. 3 significant to 

arrester applications are as follows: 

1. The non-linearity of the voltagecurrent characteristic is exceptional, a 

change in voltage of only a factor of 1 .56 bemg required to change the current 

five orders of magnitude. 

2. At all except low current densities (less than lo-' a/cm

negligible temperature coefficient, and as a result the protective 

tics are unaffected by achange in temperature of the arrester. Su

case for the presently used siliion carbide valve elements wh

negative temperature coefficient of about 0.24%/C0. The zinc 

element also exhibits a negative temperature coefficient at 

densities, but this has no influence on protective levels; how

have an influence on the thermal design of the arrester for no

voltage conditions. 

3. At very high current densities (greater than 10 a/cm2) the 

cwe begins to turn up sisnif~cantly with the turn-up attribu

resistivity of the zinc oxide grains. A voltage turn-up at high cur

is characteristic of silicon carbide valve elements as well. A

current densities encountered in arresters, the turn-up of zin

ments is much less than in silicon carbide elements. 

4. Not shown in Fig. 3 but of great significance is the fact tha

oxide valve element is subjected to very high discharge current

tive characteristics remain essentially unchanged. This is in 

silicon carbide valve elements used in conventional arresters 

exhibit increased protective levels after being subjected to imp

discharges. 

PROTECTIVE LEWL CONSIDERATIONS 

If 10 kA is assumed as the current to be used for insulation co

a given application, and ifthe I0 kA discharge voltage is 1.6 x ar

the minimum BIL that may be protected with a margin of 20% 

arrester rating. The usual assumption is that the switching sur

withstand is 0.83 times BIL; therefore, the switching surge with

x 1.92 = 1.59 x arrester rating. Employing the minimum accep

15% for switching surge protectidn, the switching surge pro

should be 1.5911.15 = 1.39 times rating. With the new zinc 

elements it is readily possible to provide arresters with a sw

protective level of 1.39 times rating and a 10 kA discharge vo

rating. With these protective characteristics a 258 kV arrester 

system could even protect 750 kV BIL equipment with a marg

impulse and 23% on switching surges. 

AIuasmR TESTS 

Protective C1. Sp~ekOv~ 

Because seriesgapsare not used, the arrester does not hav

characteristie; rather,-& valve ekments enter into conductio

accordance with Curve A of Fig. 2 as the voltage is increased a

ing level. 
2. DhrhnrscvThe Cwe of Fu. 2 indicates a diiharge voltage at 10,000 amperes of 

1.6 x crest arrester raeg wh$h is approximately the level normally given for 

cumnt limiting gap arresters. Because of the higher exponent of the zinc 

oxide curve, discharge vobtages at higher currents tend to be less than 

discharge voltages of silicon carbide valve element arresters. 

Because the arrester does not have a sparkover characteristic, an investigation was made to determine the arrester voltage level on fast front 

cumnt impulses @ order io illustrate the short time characteristics of the 

arrester. The results of tests made using 10,000 ampere waves cresting in 

0.12psec, 1.3 psec and lOpsec are given in Fig. 4 together with the results of 

identical tests on conventional silicon carbide arrester valve elements. A 

curve showing the ratio of front-of-wave sparkover to sparkover at 10 psec 

(which is avvroximately the same mamitude as the 10 kA discharge voltage 

on an 8 x U) Esec wave for aconventikl arrester) is included for reference. 

The silicon carbide valve element voltage on awave cresting in 0.12 psec is 

1.6 times the voltage measured on a wave cresting in 10psec. This is in 

accordance with previdts observations that silicon carbide valve element 

voltage increases by 8 to lWo each time the time-tocrest is halved for the 

same current magnitude. It is interesting to note that the ratio of industry' 

maximum front-of-wave sparkover (occurring at about 0.6 psec) to 10,000 

ampere 8 x 20 psec discharge voltage for arresters rated 258 kV is about 1.25 . The curve of Fig. 4, however, indicates that the discharge voltage on a 0.6 

microsecond current wave is 1.36 times higher than the discharge voltage on 

an 8 x 20 psec wave. Apparently, the discharge voltage of an arrester of 

conventional design on a fast front current wave may be at least as high as the 

front-of-wave sparkover. On the other hand, the zinc oxide valve element 

voltage on a wave cresting in 0.12 psec is 1.28 times the voltage measured on 

a wave cresting in 10 psec and the voltage for a current wave cresting in 0.6 

microseconds is only !.I6 times the voltage for a wave cresting in 10 psec. 

Therefore, for wave fronts as short as 0.12 psec the voltage across an arrester made using zinc oxide valve elements will be less than either the 

hnt-of-wave sparkover or discharge voltage on similar waves for conventional arresters. 

2.1 Stability of Discharge Voltage ChnrPcterlstics 

Stability of zinc oxide disks on high current impulses llas been measund. The adcation of two 4 x 8 ps& 65 kA impuises results in a change 

(slight decrease) iri discharge voltage of less than 2% at 100amperes and less 

than3% at 10 kA, with repetitive application of 10 kA impulse waves causing 

RO detectable change in the discharge voltage. Silicon carbide valve elements generally show much greater change. In fact, an increase of 10% in 10 

kA discharge voltajje is permitted a standard duty cycle test.' 

Discharge voltages in arresters using the new valve elements may be 

adjusted without much diiculty by arranging gaps in shunt with a small 

Portion of the valve elements. That is, the designer must provide for the 

quired total amount of valve material to assure proper operation at normal 

Operating volk&e and during temporary overvoltages above arrester rating. 

ff this results in too high a discharge voltage at the selected coordination 

Current, 10 kA for example, a small portion of the disks can be effectively 

 moved at highcurrent levels by . paralleling them with property coordinated - shunt gaps. 

.- 

TIME (u SEC) 4. 10 kA disc- voltege vs, current wave crest time for zinc oxide '* carbide valve ekments (m per unit of the lOpsec values). Cwe 

A is a264 kV amstet sparkover characteristic in per unit of the 10 kA, 8 x 

&Jec discharge voltage. 

Durability 

1. Duty Cyck Tests 

One of the most basic tests for arresters developed over the years has 

been the duty cycle test.' Very generally, this test consists of placing the 

arrester across a 60 Hz power source at rated voltage of the arrester and 

subjecting it to high current impulses once per minute for twenty four 

minutes with the impulses timed to appear at selected points on the 60 Hz wave. The Standard calls for the impulse current to be a 10 kA, 8 x 20 psec 

wave for station class arresters. The basic purpose of the test is to demonstrate durability of the arrester (ability to tolerate the impulse currents 

combined with the consequent power follow current) and its ability to reseal 

consistently at rated voltage. Itwould be expected from study ofthecurve of 

Fig. 2 that power frequency follow currenithrough the zini oxide element 

should be substantially zero at rated voltage which is 6 x fi= 8.5 kV crest. 

Nevertheless it seemed useful to perform the duty cycle test to demonstrate 

that there would be no unexpected problems. The oscillograms of Fig. 5 

illustrate such tests performed exactly as they would be on a conventional 

arrester except that a much higher sensitivity than normal is employed for 

the current trace. Fig. 5(a) shows a typical operation in which the negative 

polarity impulse was applied at about 30" before crest of the 4th positive half 

cycle on the oscillogram. Note the lack of a significant follow current on that 

half cycle although thereis undoubtedly a small short duration interaction 

current caused by the discharge voltage of the arrester forcing current into 

the inductance of the source.6 It should be noted as well that the general 

shape and magnitude of the arrester current after operation is essentially 

identical to that before the operation. Fig. 5(bl shows the 20th overation 

during the duty cycle test. The arrester eurrent trace of this oschgram 

shows a DC shift, but this is an instrumentation error caused by the 10 kA . impulse shocking the sensitive amplifier used to display these low current 

levels. In Fig. 5(b) the current after the operation was actually identical to 

that just prior to the operation. After the 20 operations the arrester current 

hadincreased from 4.5 ma zero-tocrest to about 8.5 ma zero-tocrest. Upon 

cooling back to room temperature the current was almost identical to the 

original value except for a small deviation caused by a temporary phenomenon to be described in a later section. Such a small increase in arrester 

current duringaduty cycle test is ofno consequence since the thermaldesign 

of the arrester is capable of dissipating the associated watts loss with no 

ditrrculty. 

2. Tmnsmis?iion Line Discharge Test 

The transmission line discharge test specified in ANSI Standard 

C62.1-1975 is passed readily by zinc oxide arresters. Current on the fmal 

operation is substantially identical to the current on the fmt operation of the 

test. 

3. Overvoltage Capability 

Certain applications demand that an arrester be able to survive several 

cycles of voltage above rating af€er being subjected to a relatively high 

energy switching surge discharge. For example, in picking up a line with an 

udoaded transformer and its associated arrester at the far end, the arrester 

may be subjected to a prospective voltage profile of 1.5 or more times rating 

for one or more halfcycles followed by several cycles of lower voltages still 

above arrester rating. These overvoltages are caused by reflection of traveling waves on the line as well as by harmonic currents drawn through the line 

impedance by the transformer. Such overvoltages are generally related to 

circuit confiwtions in which the current available to the arrester is limited 

by the surge impedance of the transmission lie. In order to atlow the 

application of arresters in circuits subject to short time overvoltages, most 

arrester manufacturers now supply information as to specific overvoltage 

envelopes their arresters will tolerate. For example, station arresters presently manufactured by the authors' company can tolerate overvoltages in 

per unit ofarrester rating equal to 2.0 for one-halfcycle followed by 1.3 for 10 

cycles or 1.6 for two hatfcycles followed by 1.25 for 10 cycles in circuits of 

she impedance normally associated with overhead transmission lines. 

For conventional arrester the failure mode when overstressed in this kind 

of operation is generally inability to clear because of gap restriking. Although the new arrester does not have series gaps, it is important to demonstrate that it has adequate energy absorption capability to cope with overvoltage operations. 

Fig. 6 is a schematic diagram of one test circuit which has been used to 

test the capability of prorated arrester sections under overvoltage conditions. In this circuit a generator with source inductance L1 is connected to 

the test sample, through the resistor R1 representing the surge impedance of 

the line, by closing the synchronous switch S1. One or two half-cycles later 

the source voltage is reduced by closing &itch S2 to provide a voltage 

division between U and L1. In practice the circuit inductances and switch 

timing are fust adjusted with the sample removed to establish the desired 
(b) 

Fig. 5. (a) Typical duty cycle operation at rated voltage with a 10 kA 8 x 20 

psec impulse. Large deflection trace is arrester voltage. Smaller deflection 

trace is arrester current (9 ma P-P). 

(b) Duty cycleoperation after (20) operations at 1 minute intervals. Current 

increase to 17 ma P-P is due to heating. DC shift in current trace is an 

instrumentation error. 

Fig. 6. 60 Hz dual level overvoltage test circuit. 

L1 = source inductance, L2 = loading inductance 

S1 & S2 = synchronous switches, 52 closed M or 1 cycle after S1 

R1 represents surge impedance of transmission lie 

prospective voltage envelope. The sample is then comected and subjected 

to the overvoltage test with appropriate monitoring of arrester voltage, 

current, and energy dissipation. Fig. 7 is an oscillogram of such a test on a 

prorated model of the new arrester designed to provide a switching surge 

protective level of 1.39 times rating and a 10 kA discharge voltage of 1.6 

times rating. For the results shown in Fig. 7(a) the prospective voltages for 

successive halfcycles were 2.0, 1.32,1.35,1.29,1.29, - - - etc., decaying to 

1.19 times rating on the 10th cycle, at which time the voltage was removed. 

(The reason for the decaying voltage envelope is the transient change in 

impedance of the rotating machine used as a source.) The arrester drew a 

current of 760 crest amperes in the fust halfcycle with currents of less than 

80crest amperes in the following half-cycles. The totalenergy absorbed was 

5.1 kW sec per kV of rating. 

For the test illustrated by the oscillogram of Fig. 7(b) the prospective 

voltage envelope was 1.61,1.61, 1.341.31, - - - etc., decaying to 1.24 on the 

8th cycle. In this case the arrester carried a maximum current of 450 crest 

amperes and absorbed a total of 5.3 kW sec per kV of rating. The current 

traces of bpth osciilograrns indicate exactly the currents predicted from the 

valve element volt-ampere characteristic; therefore, it is clear that the 

heating from the energy dissipated had no adverse effect on the ability of the 

ekments to limit current as the voltage returned toward nod. 

Fig. 7. Arrester operation in 60 Hz overvoltage circuit of Fig. 6. 

to bottom, are arrester voltage, arrester current, source volta

surge impedance, arrester energy. 

(a) Prospective voltages of 2.0, 1.32, 1.29, 1.26, etc. times ra

arrester current is 760crest amps. Total energy is5.1 kW SecIkV 

(b) Prospective voltage of 1.61, 1.61, 1.34, 1.31, etc. times ra

arrester current is 450crest amps. Totalenergy is 5.3 kW SecIkV 

Fig. 8. Test circuit used to generate overvoltages by switch

former terminated transmission line. 

G = Source Voltage 

S1 = Synchronous Switch 

L = Source Inductance 

T = Unloaded Transformer 

Fig. 9. Arrester operation on overvoltage circuit of Fig. 8. Tr

bottom, are arrester current, source voltage, arrester energy, 

line end) voltage. 

(a) No arrester connected, showing neg. half cycle prospective 

the arrester location of 1.59, 1.61, 1.23, 1.33, 1.40, 1.40, 1.37

arrester rating. 

(b) Arrester connected, showing max, arrester current of 460 

total absorbed energy of 4.7 kW sec/kV of rating. 
The test circuit of Fig. 6 is felt to be excessively severe because the 

applied voltage is a 60 Hz sinusoid whereas typical overvoltage phenomena 

with which the authors are familiar are always characterized by a significant 

harmonic content. The highly peaked nature of these more typical 

waveforms causes the arrester current for each halfcycle to be of much 

shorter duration than it would for a sinusoidal60 Hz voltage and consequently the absorbed energy is significantly less. For this reason the test 

circuit of Fig. 8 was developed to allow testing of arrester samples under 

conditions very similar to those actually encountered in service. In this 

circuit an unloaded transformer terminated transmission line is suddenly 

energited from a 60 Hz source which is a condition leading to severe system 

overvoltaaes. With the test sample removed. the circuit parameters includingsou&voitage, source inducke, switchcbsinganglk, and transformer 

saturation characteristics can be adjusted to give the desired prospective 

voltage envebpe. 

The oscillograms of Fig. 9 illustrate tests with this circuit on a prorated 

section of an arrester designed to provide a switching surge protective level 

of 1.35 times arrester rating. The upper oscillogram shows that the prospeclive negative crest voltag& are 1.59, 1.61, 1.2i, 1.33,1.40, 1.40, l.k, 1.37, 

1.34, 1.32, 1.30 times rating with the arrester disconnected. The lower 

oscillogram, with the arrester connected, shows amaximum arrester current 

of 460 crest amperes with a total absorbed energy of 4.7 kW sec per kV of 

rating. It is worthemphasizing that the absorbedenergy for Fig. 9 is less than 

for Fig. 7(b) in spite of the fact that the protective level is lower, the 

prosp&tive volta&s are higher and, conse&ently, the currents are also 

siso'iantly higher. As already indicated this is because the overvoltages 

an peakededrat&r than sinusoidal and it is believed that this is a far m&e 

accuiate representation of the practical condition. 

Temporary overvoltages sustained for many cycles may result from 

certain system conditions including line and transformer ene~gization, resoDance effects, or bad rejection. In such cases the abiity of an amster to 

tolerate a sustained but moderate overvoltage is of interest.' Fig. 10 is an 

oscillogram showing the new arrester designed for a switching surge protective kvel of 1.39 times rating subjected to a 60 Hz voltage of 120% of rating 

for 60 cycles. The upper trace shows an arrester cunent which settled down 

to about 14 amperes zero-tb-peak after the first few cycles wifh no evidence 

of MY distress at the end of the test. The total absorbed energy was only 3.1 

kW %%per kV of rating. It win be noted on the oscillogram that within about 

thne cycles after the voltage was applied the current had fallen to approximaklyone-third of the initial level. The phenomenonof an initiat current in 

euess of the steady state value upon ihe sudden application of a 60 Hz 

v~Ilese is a characteristic of the zinc oxide valve elements. It has been 

observed on all zinc oxide disks, but it is of no real consequence since it is 

~-t only at relatively low currents. In the protective regionof several 

hundnds of amperes, the effect nearly disappears as shown b the OSC~IIOof Fig. 11. In this test, a voltage was suddenly applied wLh forced a 

fit half cycle current of880 amperes and after 2-112 cyles the current was 

MO~pe~s which is a reduction of only 3-11% from'the initial level. 

Rg. 10. Amster operation for60cycles at 120% of rated voltage. Top trace 

mstercumnt showing 27 amps P-p after first few cycles. Centertrace 

is mWer voltage. Lower trace is arrester energy (final value is 3.1 kW wkv of rating). 

I. Clpdtor ~~shrnc A~diePtbn 

It long ban &&& by manufacturers and users of arresters that 

P"C more difticult ab~lications for arresters is in locations adjacent to 

WWitor banks. 6 basic reason for this is that as the capacitor is 

Cub the overvoltage sourn the conventional amster draws no cur- mtuM sparks over. ~t the instant of sparkover the bank is effectively a 

impsdanee source charged to arrester sparkova and the arrester impe- dQka skply that by the valve blocks at a voltage equal to the 

8~~cr voltage. At tb voltage the valve blocks will limit the current to 

no bss* about 10 kA which must then be the initial discharge cumnt into 

Depending on whether or not the prospective overvoltage is 

Ir+acert~~ster sparkover, an additional current may be available to the 

IIssster hm the energy stored in the cincuit inductance.' At this level of 

naant the arcs will stick at the starting points in the gaps and they will not 

~WY hm the starting points until the current has dropped to around 

lMOam~eI'CS0r less. If the total charge transferred while the arcs are at the 

dcl0.w electrode spacing is much more than one wulomb, severe 

Ohctrode bunaSe may result and restriking of the gap may occur. 

Fig. 11. Operation on a 60 Hz overvoltage set to force a current of about 

900 amps. Top trace is arrester current (880 crest amps 1st half cycle, 850 

crest amps on 5th half cycle). Lower two traces are arrester voltage. 

The new zinc oxide arrester starts to conduct as soon as the voltage 

approaches the protective level and only enoughcurrent is drawn to hold the 

voltage to that level. The new arrester can be expected to pass much lower 

peak currents, absorb less energy and pass a lower coulomb charge than a 

comparable conventional arrester. The advantages of the new amster in 

this application are clearly illustrated in Fig. 12 which shows the results of a 

digital computer solution for an idealized case. The circuit shown in Fig. 

12(a) npresents a 135 MVARcapacitor bank being switched from a230 kV 

system having an available current of 15,000 amperes and protected by an 

arrester (A) rated 180 kV on the source side of the operating switch. The 

prospective voltage, had the arrester not conducted, is shown by the dashed 

lines on the ocillograms. The oscillogram of Fig. 12(b) illustrates a switch 

operation with a conventional arrester and with a sparkover of 382 kV, or 1.5 

times rating, represented. The peak current drawn by the arrester was 

12,400 amperes. The charge transfer through the arrester up to the time that 

the current dropped to 1500 amperes was about 1.1 coulombs, which is a 

significant duty. In contrast, as shown in Fig. 12(c) a representation of an 

arrester made without using series gaps, but using zinc oxide valve elements 

carried a current of only 1800 amperes while limiting the voltage to less than 

1.39 times arrester rating. The energy absorbed by the arrester was o* 

about 0.7 kW sec per kV of rating. 

Clearly then in this application, the new arrester can provide superior 

protection while being subjected to far less duty than the conventional 

arrester. The reason is made clear by a study of the voltage oscillograms of 

Fig. 12. Although the zinc oxide arrester limits the voltage to a lower kvel 

than the wnventional arrester, the voltage remains at nearly aconstant kvel 

throughout the operation and the arrester extracts no more energy 6om the 

circuit than required to perform its protective task. On the other hand, the 

voltage across the wnventional arrester falls to a lower level after sparkover. As a result, the conventional arrester absorbs much more energy and 

passes more coulombs than the zinc oxide arrester. 

The ability of arresters of the new design to function properly in locations adjacent to capacitor banks was demonstrated by experience on a 

12.470 volt svstem in the midwest. In 1973 a request was received from the 

&kty to he& ?hem find a way to avoid failuref of arresters (not manufactured by the authors' company) being caused by restriking of circuit breakers used to switch capacitors at frequent intervals. Ancsters containing zinc 

oxide valve elements and with no series gaps were installed at two locations 

on the system, the locations Wing adjacent to switched capacitor banks of 

approximately 5.4 and 6.3 MVAR respectively. 

Discharge counters were installed with the new arresters and records 

kept of the counts recorded through the new arresters as well as on adjacent 

conventional arresters. The discharge counters on the adjacent wnventional arresters virtualty ceased to operate and those on the (6) new arresters 

recorded a total of 1063 counts over a 30 month period. In addition, none of 

the new arresters have been damaged by the discharge currents from the 

large capacitor banks. It must also be pointed out that the arresters suppkd 

were of a very preliminary design and the present design incorporates 

significant improvements such as improved electrical strength and stabilii 

of the disks and an improved heat transfer design. 
10 

5 

0 

TIME - MS 

20 

15 

kV k A 

10 

5 

0 

TIME - MS 

(c) 

Fig. 12. Comparison of conventional and zinc oxide arresters adjacent to a 

capacitor bank. 

(a) Circuit representation 

(b) Conventional I80 kV arrester 

(c) Zinc oxide 180 kV arrester 

STABILITY UNDER CONTINUOUS AC STRESS 

A characteristic of the zinc oxide valve element is a tendency for the low 

current end of the volt-ampere characteristic to drift very slowly when the 

device is subjected to continuous AC voltage stress as illustrated in Fig. 13. 

The low current drift is in a direction which causes an increase in the watts 

loss under normal operating conditions, and this drift coupled with the 

positive temperature coefficient of watts loss of the disk makes it imperative 

that tests be made to demonstrate that the disks will exhibit long term 

stability at the designed operating stress and temperature. A considerable 

number of life tests have been made to prove disk stability. The tests were 

made at elevated temperatures and several AC voltage stress levels with 

periodic measurements of watts loss during the tests. 

The following test information was obtained. 

a) For a given test voltage and temperature the normalized watts loss 

plotted on alogarithmic scale increases linearly with the square root of time 

after some initial elapsed time, usually several hundred hours, during which 

a slight decrease in watts loss is often obtained. This relationship is illustrated in Fig. 14. The linear relationship has been confirmed out to 6000 

hours (at the time of this writing) at elevated temperatures of up to 115°C and 

the tests are continuing. The 6000 hour test time at 1WC is equivalent to 

about 5 million hours at an expected maximum weighted average temperature of 45°C. 

b) Tests at various temperatures and several stress levels confirm that the 

rate of increase in watts loss vs temperature follows the well-known Arrhenius relationship for thermally activated phenomena. That is, the 

logarithm of the time required for a specific change in a given characteristic 

is a linear function of the reciprocal of the absolute temperature (KO). This 

relationship has been widely used in most types of life testing of thermally 

dependent electrical materials. This is illustrated in the plot of Fig. 15 

showing the time required for a doubling of the watts loss vs reciprocal 

temperature at the operating stress level for a 72% arrester application. 

experienced in locations such as Phoenix, Arizona would be app

45°C (1 15°F). This weighted average was obtained by determin

pected temperature-time profie for the porcelain housing for a ty

each of the four seasons of the year. These data were then ope

accordance with the slope of the Arrhenius curve of Fig. I5 to 

overall weighted or effective temperature for a severe applicat

shows that approximately 200 years will be required for the wa

72% arrester to double from thee'original value. The watts loss 

oxide arrester will be approximately 0.15 watts per kV of rating a

is only two-thirds of the loss for an existing conventional desig

I 

CURRENT (LOG SCALE 

Fig. 13. Illustration of drift in volt-ampere characteristic with 

under a continuous AC voltage stress. 

Fig. 14. Illustration of watts loss vs. time for a continuous A

stress at elevated temperature. 

EFFECT OF IMPULSE DISCHARGES AND HIGH ENERGY 

When the zinc oxide disks are subjected to short duration im

ning) discharges or to high energy long duration (switching surge

the low current end of the volt-ampere characteristic curve is s

right causinga temporary increase in watts loss much as illustrat

term stress in Fig. 13. Forexample, the watts loss roughly doubl

of 20 applications of 10 kA, 10 x 20 psec waves. The watts loss 

by approximately a factor of 1.5 by the application of twenty 100

millisecond switching surge discharges. 

In all cases, however, the effect is temporary. Since station ty

are rarely subjected to more than a few discharges of significan

per-year, such discharges will not affect the operating cond

arrester. 

SURGE ENERGY CAPABILITY 

For any single event the disks designed for arresters rated 

lower are capable of absorbing9 kW sec.lkV of rating. For exam

1000 ampere discharge of about 4 millisec. duration is permi

greater energy absorption in a single operation may result in di

from thermal shock. After absorbing up to 9 kW sec./kV of ratin

operation, an interval of 1 to 2 minutes is sufficient to permit equ

temperature throughout the disk, after which additional energy a

permissible up tothe limit imposed by transient thermal &bi

perspective onenergy absorptioncapabiiity may be gained by no

stored energy in the line used to perform the standard transm

discharge tests for 345 kV system arresters is less than 4.5 kW 
Fig. IS. Arrhenius plot of zinc oxide valve element life vs. reciprocal 

temperature with a 60 Hz operating voltage. 

wester rating, and the energy actually discharged by a 72% zinc oxide 

Wster is less than 3 kW sec./kV of rating. 

Zinc oxide valve elements exhibit a positive temperature coefficient of 

watts loss as shown by Curve 1 of Fig. 16. Such a relationship between watts 

loss and disk temperatwe makes it necessary that the design incorporate an 

&equate heat transfer mechanism to insure that the watts loss at openth 

voltage will not be driven beyond the dissipation capability. To hsure 

$lability following high energy discharges, the arrester has been designed 

w?th the relatively massive porcelain housing serving as a heat sink for the 

dl?ks, Rsulting in a heat transfer capability in accordance with Curve 2 of 

Fl~. 16. Curve 2 of Fig. 16 was determined for a porcelain temperature of 

f@c which is the short-time maximum temperature anticipated in a location 

Phoenix, Arizona. Curve 1 gives the watts loss versus disk temperaa Pornlain temperature of 60°C. is at the lower crossover point of Curves I 

2 (0.28 watts per kv of rating and 63°C). When the arrester discharges 

'U'Bc energy, the disk temperature will rise by approximately 7.6"C per kW 

FC./kV of rating. As shown by Fig. 16, instability would theoretically Occur 

arthe disk temperature was raised to the upper crossover point of Cu~e 1 

Fd2 (when the watts generated in the disk equals the heat transfer capabil- 

"Y of the design), This point is 13f C above the operating point flower 

CmJSO~er ofcurves 1 and 2) so surges of a total energy equal to 13517.6 = 

kW Sec./kV of rating can be tolerated. This is over three times the 

'"WY absorbed from operation in the overly severe test circuit of Fig. 6, 

neetl~ four hes the energy absorbed from operation in the more realistic 

Cimuitof ~b. 8, and approximately 3 times the total energy absorbed in a 24 

O*reth standard duty cycle test. Furthermore, 17.7 kW sec. IkV is ap 

twice the maximum discharge energy that can be absorbed a 

1 , 0 5 10 15 

ASSOCIATED kW SEC/kV OF RATING 

Fig. 16 Watts loss and dissipation characteristic curves. 

1. Watts loss vs. temp. at operating voltage (72% arrester application). 

2. Thermal dissipation capability of the arrester. 

3. Possible watts loss vs. temp. after many years of service. 

single operation without causing thermal shock failure of the disks. Even in 

the extreme case of operation based on Curve 3 of Fig. 16, the allowable 

energy absorption is 14.8 kW sec./kV of rating which is well above the 

capability of the conventional arresters. 

From the above, it can be concluded that the new arrester will give 

excellent performance even under the most severe switching overvoltage 

situations. 

CONTAMINATION PERFORMANCE 

A major problem which has confronted arrester users over the years is the 

possibiility of arrester damage and even failure when the arresters are applied 

in severely contaminated environments. With conventional arresters the 

problem is basically the possibility the svarkover may be de~ressed to 

operating voltage levels at least for short periods of time: The poker follow 

current, normally associated with each operation can very quickly cause 

overheating of the arrester and possible failure through loss of clearing 

capability. 

The ANSI Standard contamination test' can be passed very easily by the 

new design. Because the standard test produced practically no effect, more 

demanding tests were performed. The arrester was contaminated using 

multiple coatings, with drying between applications, of a 400 ohm-cm slurry 

as specified in the ANSI Standard except that Cabosil was substituted for 

Bentonite in order to obtain a more tenacious coating. Wetting was accomplished in a polyethylene tent using steam pots. Voltage was removed 6om 

the arrester for approximately 30 minutes after application of the fog in order 

to wet the arrester thoroughly. Whenoperating voltage was applied, leakage 

current pulses exceeding 100 milliamperes were measured, and occasional 
external flashovers occurred. At a level of fog wetting sekcted to produce 

maximum leakage current pulses of 50 to 100 milliamperes, the arrester was 

energized for several hours. Temperature measurements on the internal 

Darts showed a low kvel of heating well within tokrable limits. Contaminaiiomtest performance of the new design compared with test experience of 

existing designs, which have performed very satisfactorily in service, indicates that the new design has outstanding capability to withstand the effects 

of very severe external contamination. 

I. Thc development of zinc oxide based non-linear resistors has progressed to the point where large high energy disks are m availabk permitting the manufacture of all ratings of station type surge arresters without 

series gaps and with protective characteristics superior to present designs. 

2. The new arrester offers some very significant advantages: 

a) Lmpmved reliability due to simplicity of the design; 

b) Superior protective characteristics. 

C) Minimum energy absorption commensurate with the protective levels 

provided; 

d) Superior performance compared to present arresters on low impedance 

circuits (e.g. cable and capacitor applications); 

e) Gentle operation -protected equipment is not subjected to sparkover 

transients; 

f) Superior energy absorption capability compared to presently available 

arresters. 

3. Extensive tests have demonstrated a performance which is entirely 

satisfactory. 

The authors wish to gratefully acknowkdge the following individuals who 

contributed significantly to the success of this work: Herbert Fishman, 

Howard ~llis,and Dr. ione el Levinson, all of the General Electric Company. 

E.C. Sakshaug, "Current Limiting Gap Arresters - Some Fundamental Considerations," IEEE Transactions (Power Apparatus and 

Systems), Vol. PAS-90, No. 4, pp. 1563-1573, JulyIAugust 1970. 

DJ. Melvold, S.A. Miske, E.C. Sakshaug, "Switching Cables Can 

Stress Arresters," Electrical World, May 15, 1974. 

E.W. Boehne, "Discussion of Ref. 6) below," IEEE Transactions 

(PAS), Vol. PAS 84, No. 6, pp. 535, June, 1%5. 

American National Standard C62.2-1%4, "Guide for Application Of 

Valve-Type Lightning Arresters for Alternating-Current Systems." 

(Including revised Appendix A, 1972.) 

American National Standard C62.1-1975, "Surge Arresters for Alternating Current Circuits." 

E.C. Sakshaug. TJ. Carpenter, and E.W. Stetson. "Duty Cycle 

Testing of Cmnt Limiting Station and Intermediate Lighw Arresters." IEEETranwtions (PAS), Vol. PAS-84, No. 5, pp. 442-425, 

May 1%5. 

H.C. Barnes, "Preliminary Analysis of Extensive Switching Surge 

Testinn of American Electric Powers First 765 kV Line and Stations," 

~~~~'Traansactions (PAS),Vol. PAS-90, No. 2, MarcYApril 1971. 

Discussion 

Bernard F. Wirtz, (Cleveland Electric Illuminating Co., Cleveland, OH): 

The authors' new arrester without gaps is very suitable for installation 

inside of an SF6 gas insulated substation. Eliminated is the concern that a leak would allow SF6 gas to enter the gap chamber and change the 

protective characteristics of the arrester. Are the authors in a position 

to comment on this new arrester in GIs installations? 

In the section dealing with "Stability on Continuous AC Stress", 

the authors demonstrate the arrester's capability in a "Phoenix" weighted average ambient temperature of 45 degrees C. Would the authors 

comment on the suitability of the new arrester, if installed in metalclad 

switchgear, where the air inside of the cable exit compartment is allowed to reach 55 degrees C while the equipment is carrying rated continuous current and the outside or room ambient temperature is 40 degrees 

C? (See ANSI C37.0204.4.5(1).) Under emergency conditions, when 

Manuscript received July 19,1976 

currents may exceed the rated values, the temperature insi

closure will be higher, perhaps by 5 or more degrees C. 

Similarly, the total temperatures of conductors and o

carrying parts of circuit breakers and disconnecting switc

allowed to reach 105 degrees C at rated conditions and o

grees C under emergency conditions. Can the arrester a

these temperatures at its connection terminal, or are oth

required? In capacitor bank applications, the new arrester's un

of turning on smoothly before the voltage approaches t

level of contemporary arresters and of its ability to con

voltages without absorbing excessive energy are welcome as 

to load up our 37 kV substation buses with 160 MVAR's o

We use arrester counters to monitor all arresters and to ru

restrike problems on the capacitor switches operated dail

authors indicate at what minimum level of arrester voltag

the counter will register a count with their new arrester? 

On all station type arresters we have required press

vices. The authors do not mention pressure relief devices. 

authors handle this protective requirement? 

Orin W. Queen (Dayton Power and Light Company, Dayto

paper presents the development and testing of a new s

which is the first significant improvement in a number of y

comes the main disadvantage of the current limiting gap a

proving performance on low impedance circuits. The volt

teristic is so good in the 0.1 to 1.0 microsecond area that 

front-of-wave impulse testing of transformers might be eli

high overvoltage capability of the new arrester will make 

use a lower voltage rating in some application which w

better protection hd a lower cost. Shipping damage and d

vibrations when mounted on transformers have been a pr

past. What has been done to the new arrester to eliminat

lems? What tests are recommended on the new arrester 

that it is satisfactory for continuing service? Leaking seals ar

arrester problem. What is the affect of moisture on the n

ment? The elimination of gaps should improve the radio 

ference problems. Were any tests made to confirm this p

The Author's Company has developed a new arrester whi

of considerable value to the Electrical Utility Industry. I 

the Authors on a very informative and complete paper. 

Manuscript received August 9, 1976. 

J. C. Osterhout and A. Sweetana (Westinghouse Electric 

Bloomington, Indiana): The authors are to be commen

early publication of data on a zinc oxide based surge arrest

ly of the station class. 

The protective level of 1.6 times arrester rating at 10

as indicated, is approximately the same as presently avai

the art arresters. To maintain the protective level at higher 

authors require paralleling of a small portion of the disks "w

coordinated shunt gaps". It is clear from this requirement 

linear exponent of the zinc oxide disk is not high enough a

development to permit a truly gapless arrester. Our calcula

that the authors have achieved a non-linear exponent of a

26. Depending on protective level to be achieved, an exp

proximately 50 is required for a truly gapless arrester. It 

that the suggested interim hybrid device may have limited 

particularly if an economic premium is to be paid. The Westinghouse Electric Corporation has also uti

funds and technical resources for several years and recen

cooperative effort with the utility industry, through EPR

this hybrid stage; setting as an objective a true gapless 

protective level of 1.5 P.U. of maximum line to ground vol

imately 1.2 P.U. of arrester rating based on an 80% arres

amperes. Will the authors please comment on the following que

1. In regard to the effect of impulse discharges and 

surges - The authors state the volt ampere characteristic 

to high current impulses, "in all cases, however, the effect i

The Japanese literature for example, "Gapless Lightning 

Power Systems" written by Syuniti Hieda, Misao Kabaya

621.3 16.9; Meiden Review, Series No. 46 1975 No. 2

thermal treatment of 150°C for 3 hours is needed to resto

to within 376, beyond which it cannot be corrected. Therm

is also indicated in, "High Voltage ZNR Surge Absorber" 

Eda et al, in National Technical Report, Vol. 21, No. 

pp. 109-122. Have the authors encountered this pheno

Manuscript received August 12,1976. 
course of their development? Have they examined the effect at higher 

current levels, say 20,000 amperes? Does temporary mean seconds? 

hours? 

2. Since no photographs or dimensions were given, can the 

authors indicate a relative or copmarative size and weight of the zinc 

oxide based hybrid arrester with a conventional modem arrester. 

3. Can the authors give an indication of the actual number of 

poles in service and time in service on 230 kV or higher voltage systems? 4. It is not clear what the apparent exponent of the discs or total 

hybrid device is to currents higher than 10,000 amps. ANSI C62.1-1975 

requires measurement of discharge voltage through 20 kA, and it is com- mon Industry practice to publish protective characteristics through 40 

kA for station class arresters. Can the authors achieve present arrester 

level of protection at 20, 40, 65 kA with the shunt gap apporach, yet 

leave enough discs in the circuit for power current interruption at maxi- mum system voltage? 

D. J. Melvold (Department of Water and Power, Los Agneles): The 

authors are to be commended for developing what appears to be an ar- rester with characteristics closely resembling the long sought "ideal" 

arrester. This arrester appears to make the controversy over the correct 

lightning current level to use for station insulation coordination a rather 

moot point. 

Our interest, however, extends beyond the use of the arrester on ac systems to which the authors have directed their discussion. Have the 

authors extended their investigation to the application of this arrester to 

dc systems? If so, could they elaborate to some extent on their studies 

to date? Offhand, it would appear from the more horizontal voltampere characteristic, that the potential for considerable reduction in 

margins is possible in dc installations along with better coordination 

with such devices as thyristor values. With regard to the latter, the more "gentle operation" - i.e. no AV as occurs subsequent to sparkover in 

conventional arresters - would be desirable, e.g., across the smoothing 

reactor. 

In addition, with regard to dc applications, it is noted that under 

the section on Stability Under Continuous AC Stress, the authors 

specifically state "ac". What if the stress were essentially a dc voltage? 

Would the authors comment on the possibility of using this arrester instead of a resistor in a circuit breaker for overvoltage suppression or using a zinc-oxide resistor within either ac or dc circuit breakers? 

Lastly, what is the comparative size and weight of this arrester in 

relation to a conventional arrester of the same rating? 

Manuscript received August 16,1976. 

U. Burger, H. P. Klein, and B. Knecht (BBC Brown, Boveri and CO., 

Ltd., Baden, Switzerland): The report shows that the new nonlinear re- <Islance material based on zinc oxide is able to perform as a high voltage 

arrester. The main advantages of these nonlinear resistors are the simplicity of their mechanical assembly (a sintered bsdy is the only active 

Part) and their favourable characteristic which allows no follow current 

minimizes the energy absorbed by the arrester. 

The following comments should however be made: 

For a residual voltage at 10,000 A of 1.6 X crest arrester rating the 

resistor has to be used in the flattest part of the currentv~ltag characteristic i.e. from Fig. 3 between a current density of 10-5 8 and 102 ~/cm2; above and below these values the slope of the 

I- V-cWve increases very quickly l,2. This implies a minimum cross-sec- 'Ion of the zinc-oxide ceramic of 100 cm2. Let us as an example con- 'Ida a 1 kV arrester (RMS rating), which we want to use in an applica- 

'Ion where the residual voltage at 10 kA is 1.6 X crest arrester rating = 

V. We therefore write for the current-voltage characteristic 

W = 4.56 ? 27 Watts. 

If lhe crest applied voltage \j is equal to the crest arrester rating 1414 V, 

Ihe watts loss is therefore 5 W. 

fhu~ for any arrester of this type the watts loss with an applied equal to the arrester rating is 5 W/kV of rating at room temPeraturc and Presumably more at higher temperatures. If we plot the 

carresWnding point on Fig. 16, we see immediately that it lies well 

'bovc the thermal dissipation capability curve; therefore such high losses 

kuxript received August 16, 1976. 

cannot be dissipated. Thus the arrester can work at this voltage for a very short period of time only, otherwise thermal runaway will set in. 

Application for a significant period of time of a voltage equal to the 

arrester rating is only possible if one allows the ratio of residual voltage 

at 10,000 A to the crest arrester rating to be about 2.2 instead of 1.6. 

It should be emphasized that Fig. 15 is only valid for ac applied 

voltage. From the data sheet for small GE-MOVB for low power appli- cations the deterioration under applied dc voltage is considerably more severe as well as faster. Thus HVDC applications of these new elements 

of these new elements requires further studies. 

REFERENCES 

[l] M. Matsuoka; Japan J. Appl. Phys. 10,736 (1971). 

[2] L. M. Levinson and H. P. Phillipp; J. Appl. Phys. 46, 1332 (1975). 

E. C. Sakshaug, J. S. Kresge, and S. A. Miske, Jr.: The authors wish to 

thank those who have submitted discussions to the paper. 

Mr. Wirtz has pointed out some of the potential advantages of the 

new arrester in gas insulated substations. While we believe that the new arrester will be well suited to this application, we have not yet proven 

that zinc oxide valve elements will operate in a stable manner in an SF6 

atmosphere. Tests are being made to assess this capability. Metal clad 

switchgear installations, in common with other installations, must be 

considered in terms of weighted average temperature rather than maximum. The maximum porcelain temperature in the Phoenix area is ex- pected to be 60°C, and exposure to this temperature or even higher 

temperatures for short times is not a matter of concern as long as the 

weighted average temperature does not exceed 4S°C for a 72% arrester 

application. If the weighted average temperature is higher than 4S°C, it 

may be necessary to increase the arrester rating to compeqsate for the 

increased temperature if a service lifetime approximating that shown by 

Figure 1 5 is expected. Temperature weighting is accomplished by noting 

that the temperature effect doubles for each 6OC rise in temperature. 

That is, 5 hours at SO0, 9 hours at 44OC and 10 hours at 38OC yields an average weighted temperature of 44OC for a 24 hour period as compared 

to an arithmetic average of 42.7S°C. The effect of high temperatures of 

current carrying conductors on the arrester temperature must be con- sidered, and it would probably be desireable to separate the arrester 

terminal from the high temperature conductors by a few inches of lead 

length of relatively small diameter wire. 

It is not possible to comment on the current sensitivity of counters 

supplied by other manufacturers, but the counter marketed by the 

author's company will count for discharges exceeding approximately 

500 microcoulombs. This is equivalent to an average current of 50 am- peres for 10 microseconds. 

The new arrester will be equipped with a pressure relief arrangement similar to that used in conventional designs. Pressure venting will 

be accomplished by means of pressure sensitive diaphragms with arc gas 

directing arrangements made to cause external flashover for high failure 

currents. 

Messrs Burger, Klein and Knecht have calculated correctly that the 

watts loss at rated voltage for a gapless arrester with a characteristic as 

shown illustrated in Figure 3 is in the range of 5 watts. It is important 

to note that high voltage arresters, certainly those designed for operation on systems rated 230 kV or higher, do not operate at rated voltage 

for longer than the several cycles required to clear a line-to-ground fault. 

Normal operating voltage for a high voltage arrester is approximately 

80% of rating, and as stated in the paper, the watts loss at normal operating voltage is approximately 0.15 watts per kV of rating. The arrester 

will pass the ANSI C62.1 Standard duty cycle which requires that the 

arrester be held at rated voltage whild it is subjected to impulses of 

10,000 ampere magnitude with the impulses spaced one minute apart, 

and this is the definition of arrester voltage rating provided by the ANSI 

Standard. This method of performing the duty cycle test is, of course, more severe than that given in IEC 99-1 which permits the arrester to be 

deenergized between impulses. As indicated in the paper, moreover, the 

residual voltage at high impulse current can be reduced by shunting a 

small percentage of the valve element with gaps arranged to spark over on high current surges. This permits an increase in the valve element 

resistance to reduce the steady state heating while maintaining the desired residual voltage characteristics, and allows the ratio of olierating 

voltage to residual voltage to be changed within reasonable limits. 

The efforts of Messrs Osterhout and Sweetana to improve the exponent of zinc oxide material beyond its present state of development 

are commendable. It is our hope as well that valve disks having further 

improved exponent characteristics will be developed in the future; 

however, as has been shown in the paper, arresters designed using the 

zinc oxide disks that have been developed have protective characteristics 

and reliability superior to existing conventional arresters. It is doubtful 

Manuscript received September 22, 1976. 
arresters having a protective level of 1.2 times rating at 26,000 amperes. 

On the other hand, the curve of Figure 3 shows that the ratio of protective level to rating may be improved by increasing the disk cross section, 

and this effect together with the judicious use of shunt gaps could result 

in an arrester having approximately the protective levels being sought 

by Messrs. Osterhout and Sweetana. 

Thermal treatment of disks to restore a temporary change in low 

current characteristics is neither necessary nor practical in an arrester 

designed using the disks described in the paper. There is no shift whatever in protective characteristics because the disk-characteristics do not 

change at high current. The low current shift lasts for a few days and is 

small. and needs only to be taken into account in the design of the heat 

transfer system. 

The only arresters of this design in service now are those involved 

in the protection of the capacitor banks referred to in the paper. It is of 

interest to note that three of the arresters from this installation were re- turned for inspection after approximately three years of service. Laboratory tests revealed no change in characteristics after over 1000 operations had been recorded even though the valve elements in these arresters were not nearly stable enough to meet our present stability criteria. 

Field experience can be very revealing if laboratory work is not care- fully done, but it is rare that acombination of environmental and system 

conditions can be found which will stress an arrester sufficiently to 

demonstrate in a reasonable length of time that the arrester will have a good field service record. As would be expected from the shapes of the zinc oxide and silicori 

carbide curves shown in Figure 3, the level of protection of an arrester 

made using zinc oxide valve elements is better than that obtained using 

silicon carbide valve elements at currents above 10 kA when the level of 

the two arresters is the same at 10 kA. 

We thank Mr. Queen'for his comments, and we agree with the 

points he has made. Mr. Queen has asked several questions regarding 

reliability. The new arrester will be much less susceptible to ship 

ping and vibration damage than older designs because of construction simplicity. In addition, the heat transfer arrangement is used to 

y gg

very probable that a sealing system is not necessary. Field test

mended for a demonstration of serviceability are leakage curre

urements at operating or rated voltage. Leakage current measu

are very effective for the new arrester because the operating com

are being measured whereas a leakage Current test on a conv

arrester measures the condition of a grading System in parallel 

operating components. Tests have indeed confirmed that potent

and TV interference are considerably reduced. 

Mr. Melvold's interest in DC applications is appreciated. 

under operating stress is known to be a function of wave shape

plications of DC arresters without series gaps $1 be made o

the completion of adequate stability studies uslng proper rep

tions of applied voltage wave shapes. The actual wave shapes en

ed in practical DC systems are sufficiently complex and varied t

rather extensive studies. We agree that there should be signif

vantages gained by the use of zinc oxide arresters in DC applica

the reasons Mr. .Melvold has mentioned. It Was announced 

author's Company in 1975 that the DC arresters recently sup

two DC projects utilized zinc oxide valve elements, but includ

gaps to isolate the valve elements from operating voltage. G

included in these designs because sufficient knowledge of the e

the voltage waves to be applied to these arresters had not 

obtained. The use of zinc oxide valve elements permitted a con

simplification of the series gaps, an improvement of protective c

istics and a reduction in arrester size compared to the arresters 

for the West Coast DC Intertie. 

It is reasonable to expect that there might be a conside

vantage in using zinc oxide resistors for surge suppression in 

and AC circuit breakers. 

The heights of the new arresters are approximately the sa

heights of conventional arresters because these heights tend to 

strike and creep requirements. Weights are in the range of 213 

the weights of conventional arresters because of the reduction 

lain diameter.