Varistor versus Environment: Winning the Rematch

François Martzloff, Life Fellow, IEEE

National Institute of Standards and Technology

Gaithersburg MD 20899 USA

f.martzloff@ieee.org

© 1986 IEEE

Reprinted, with permission, from IEEE Transactions on Power Systems, Vol.PWRD No.3, April 1986

Significance:

This paper is listed under four categories of the Annotated Bibliography as it bears on the corresponding topics. 

The multiple listing reflects the sections in which this paper is cited as supporting material for IEEE Std C62.41.1

and C62.41.2. Therefore, it can be found in the following four parts of the Anthology:

Part 2 Development of standard – Reality checks

Provides an example of the need to recognize capacitor switching transients when characterizing the surge

environment

Part 3 Recorded occurrences, surveys and staged tests

Provides an example of monitoring and staged tests motivated by field failure, leading to a better understanding of

the environment in which SPDs were expected to perform.

Part 4 Propagation and coupling of surges

Provides an example of how far (3000 meters) the low-frequency transients generated by capacitor switching can

propagate, unabated, in a path involving two step-down transformers.

Part 7 Mitigation techniques

Provides an example of improved mitigation design based on field experience
VARISTOR VERSUS ENVIRONMENT: WINNING THE REMATCH 

Francois D. Martzloff, Fellow IEEE 

Corporate Research and Development 

General Electric Company 

Schenectady, New York 12345 

Abstract - An unusual case of difficult application of surge 

prntective devices was solved by field measurements with retrofit 

of protective devices suitable for the particular environment. Onsite measurements indicated that capacitor switching transients 

were causing excessive current surges in the varistors and fuses 

protecting the input to a thyristor motor drive. Knowledge of the 

environment gained by the measurements allowed understanding 

of the probieiti aiid sp&biioii of maiching siirge ijioi&i~a 

devices. 

SUMMARY 

During the initial startup of a solid-state motor drive in a -L--..:--l ..r.-.-ano:..n ..lnrt .4:ffin..ltiar r.r;th +ha .rar:ntnr --A ,,,*G,..,ra, p'vr&,D,,& p,u.,L, uu"ru,,,"* U.U*" ",.A. .SAW .n..*. ". "%I" 

its protective fuse at the input of the thyristor circuits. Frequent 

blowing of the fuse was observed, with occasional failure of the 

varistor. On-site measurements of the voltages and currents at the 

input to the drive indicated that switching transients associated 

with the operation of a remote substation capacitor bank and the 

relatively low clamping level of the varistor were producing current 

above the fuse and varistor ratings; hence the short lives of these 

two components. When the actual conditions at that site were 

determined by measurements, it became possible to specify surge 

protective devices capable of withstanding that environment. Immediate relief was secured by the installation of a larger varistor at 

the same point of the circuit; long-term protection was obtained by 

the addition of a gapless metal-oxide varistor arrester on the primary side of the step-down transformer feeding the drive. The 

situation has been changed from failures occurring every few days 

to no further problems in the 3 years since the larger varistor was 

insiaiied. 

INTRODUCTION 

This paper presents a case history illustrating how surge protective devices that are successfully applied for the majority of cases an ~ccasiana!!y snKe: fzi!u:e when ~YPOECC! to exceptio??~!!~ 

severe surge environments. This paper also shows how little 

attenuation occurs, at the frequencies produced by switching 

surges, between the distribution level (23 kV) and the utilization 

level (460 V), even though a long line and two step-down 

transformers exist between the source of the transient and the 

point of measurement. 

85 SM 365-2 A paper recommended and approved 

by the IEEE Surge Protective Devices Committee of 

the IEEE Power Engineering Society for presentation at the IEEE~PES 1985 Summer Meeting, Vancouver, 

B.C., Canada, July 14 - 19, 1985. Manuscript submitted February 1, 1985; made available for printing April 22, 1985. 

The problem involved a 460 V power supply to a thy

drive circuit in a chemical processing plant extending over s

square miles. During the initial startup, difficulties arose wi

varistor and its protective fuse at the input of the thyristor ci

Frequent blowing of the fuse was observed, with occasional 

of the varistor. The plant substation, fed at 23 kV from the 

utility, included a large capacitor bank with one-third of the 

"...:+"l.c\* -.. nr.4 .-.a- *A ...,...:A- ..,...,&.. Fnr+,.. ne.4 ".rota- .,

anlrnlru uu uzau ULL rv pvrnur yvnrn larrur auu ojururlr r

regulation. These frequent switching operations were suspec

generating high-energy transients that might be the cause 

failure of the fuses and varistors, because literally thousan

similar drive systems have been installed in other loc

without this difficulty. On-site measurements performed 

repeated blowing of fuses and occasional failure of varistor

nected at the input to the thyristor drive indicated that inde

devices were not matched to their environment. From this 

on, specifying larger sizes, sizes appropriate to the enviro

[ll, solved the problem. 

POWER SYSTEM AND SWITCHING TRANSIENT

Figure 1 is a simplified one-line diagram of the sign

elements of the power system causing the varistor failures

incoming 115 kV power is stepped down to 23 kV. Three 

of 5400 kVAR capacitors are connected to the 23 kV bus. T

operating conditions involve two banks connected at all 

with the third bank switched on or off automatically to p

voltage regulation. Power distribution throughout the site i

at the 23 kV level. 

The various drive systems which experienced the difficu

supplied at 460 V by a 2300/460 V transformer in their c

house. A substation close to the control house suppli

2300 V power from the 23 kV distribution system. 

SiTE 

SUBSTATION DISTRIBUTION SYSTEM HOUSE i cONTROL 

I 

CONTR

CUBIC

VARISTORS 4 

0885-89/77/86/0004-0059$01.00@1986 IEEE 
gppp

input. In the original circuit. the thyristor modules were protected 

by varistors at the power input of the 1250 hp drive, where the 

measurements were made. A 6 line inductance, L1, was 

inserted between the bus and the thyristor modules; 20 mm 

varistors rated 510 V were connected in a delta configuration, in 

series with a current-limiting fuse in each line. The varistor confieciioii via3 about 80 ciii loag, in:iodi;cing an e3tima:ed ! jiH 

inductance into each lead. 

TO CRO 

11- 

- Ll - - 3 THYRISTOR a+--'-' 1- / MODULE 

a 

[ IDENTICAL CIRCUIT TO THYRISTOR MODULE 

Figure 2. Simplified three-phase schematic 

Instrumentation and Measurements 

Oscilloscopes were used to measure voltage across one varistor 

and its connection and currents through all varistors. Voltage 

measurements were made phase-to-phase on the floating delta 

460 V bus bars with Tektronix P6015 1000:l probes, connected to 

a Tektronix 7633 storage oscilloscope in differentia mode. Current measurements were made with a Tektronix CT5 20:l current 

transformer coupled with a P6021 current probe and connected to 

a second Tektronix 7633 storage oscilloscope. 

The trigger modes used during a two-hour monitoring period 

inciuaed posiiive or negaiive siopes for both siow ac and highfrequency modes. For the various modes, the level was adjusted 

to produce a trigger for a voltage exceeding the normal line voltage crest by about 20°/0, or a varistor current in excess of 2 A. No 

trigger occurred during the monitoring period. A low-frequency 

voltage recorder installed by plant personnel produced a recording 

characterized as representative of an unusually quiet day in the 

power system operations. 

Manual off-on switching of the 5400 kVAR capacitor bank at 

the 23 kV utility substation was the next step in the measurement 

procedures because the switching of a capacitor bank is always a 

prime suspect for producing transients. Measurements were performed with one oscilloscope monitoring the line voltage upstream 

of the line inductors (Figure 2) and another oscilloscope monitoring the sum of the currents in the three varistors (Figure 3). 

Figure 3. CT connection for recording 

all three varistor currents 

-. 1ne osciiiogiams of Figure 4 show typicai voitage recordi

made during this sequence. The voltages are not open-circuit tr

sient voltages. They are instances of the voltage appearing at 

bus entrance point. This voltage is the sum of the varistor clam

ing voltage, the voltage drop in the varistor connections, and 

voltage across two L1 inductances. 

A typical total event recorded on one of the phases durin

capacitor bank closing is shown in Figure 4A. A low-frequen

oscillation with a period of 3 ms (330 Hz) and initial peak-to-pe

amplitude of 450 V decayed in about 10 ms. The high-frequen

oscillations are resolved in the recording of Figure 4R (record

during a similar switching sequence). This high frequency has 

initial peak-to-peak amplitude of 2000 V, decaying in about 5 m

The period is 180 ks (5.5 kHz). A similar, third event is shown 

Figure 4C. For scaling the amplitudes, the steady-state voltage 

shown in Figure 4D. 

A Sweep: 2 ms/div Vertlcal: 500 Vfdlr 

B Sweep: 0.5 msldlv 

Vert1c.l: 500 Vldiv 

C Sweep: 1 msldlv 

Vertlcal: 500 Vldlv 

D Sweep: 2 maldlv 

Vcrticd: 500 Vllli 

Figure 4. Capacitor switching transients 

and steady-state voltage 

Observe that, depending on the time of clos~ng with respect 

the 60 Hz voltage, the 5.5 kHz oscillation varies in amplitu

f,lrtherrr?ore, !he modc!atic)n by the 330 Hz osc!!!ntlcn pcsh

crests of the 5.5 kHz oscillation above the 1000 V level some ti

after the beginning of the trace, at a time when the 5.5 kHz amp

tude is already lower, producing a burst of pulses above t

1000 V level. 

The significance of this finding will be discussed next; w

reference to Figure 5, which shows recordings of transient c

rents in all of the three varistors. The 510 V varistor has a nom

nal voltage at 1 mA [21 in the range of 735 V to 970 V. For 

varistor with a nominal voltage in the middle of this range, a c

rent in the order of tens to hundreds of amperes will flow if 

..-B.~-- ,.r jnnn TT :- ---$:-A vwrrat;E; wi lwww r 13 app~~cu io ih2 iiiiii~i~i. Figure 5A show

train of current pulses in the range of 10 to 40 A. In the burst 

Figure 5B, the recorded current pulses range from 5 A to 200 

The current and voltage traces are not simultaneous eve

because each of the two oscilloscopes was triggered by its inter

circuit. The nearly symmetrical appearance of this burst can 

compared to the symmetry of the voltage peaks exceeding 

1000 V level in Figure 4, the one correlating with the other. 

The oscillograms of Figures 4 and 5 were selected as m

severe from a series of 20 capacitor switching sequences. So

sequences could not even produce a current or voltage trigg

tour sequences produced bursts w~th the central peak exceed

120 A, two of these reaching 200 A peaks. 
A Sweep: 0.2 ms/di, 

Vertical: 20 A/dlv 

I3 Sweep: 8.5 msldlv 

Vertlcsl: 40 A/div 

Figure 5. Current surge bursts during capacitor switching 

These recordings establish the nature of the current surges that 

are conducted by the varistors, with an estimate of 10% reaching 

200 A maxlmum crests and another 10% reachmg 120 A crests, ,-A- ..,, -----:*..- L..-,. :'-L:-- IUI a11 bapabnul uaun SWILLIIIII~. 

In F~gures 4 and 5, we note that the characteristic appearance 

of the voltage and current usually observed during a switch 

restrike is absent 131, indicating a clean switching action of the 

vacuum interrupters used for switching the capacitor bank. Restrikes are most likely to occur during de-energizing. In all the offon switching sequences of this test series, no significant transient 

was observed during de-energizing; all occurred during energizing. 

The oscillograms of Figures 4 and 5 establish and explain the 

pattern of current pulses. The voltages of Figure 4 are not the 

open-circuit voltages impinging the drive input but, rather, the 

voltages resulting from the clamping action of the varistors. To 

better evaluate the magnitude of the switching transients, opencircuit voltages were recorded in a next sequence, with all fuses to 

the drive open, thus disconnecting both the varistors and all sensitive loads. Figure 6 shows two typical recordings of open-circuit 

voltages and two of voltages resulting from varistor clamping, 

recorded during a series of 10 switching sequences for each condition. Tabie i shows the recorded crests of the five highest voitages in each condition; the di!Te:ence bekeen the :wo gioiips, 

with due allowance for the imperfect statistical basis of the observations, indicates that the 510 V varistors reduced the peaks from 

a typical high of 1450 V to a typical high of 1100 V. 

Open-Circuit Voltsges 

With 20 mm Varistors 

All Traces: Sweep: 0.5 nts/div 

Vertical: 500 Vldiv 

Table 1 

FIVE HIGHEST TRANSIENTS 

IN SEQUENCE OF 10 SWITCHINGS 

Without Varistors I With Varistors I 

DISCUSSION 

Nature of the Transients 

The absence of any transient (over 120% of normal 

during ihe 2-hour moniroring period was somewhat surprls

!he cestex! ef ear!ier repc:!s cf high ccun% :cc~ibed wi:h E

disturbance analyzers. Frequent checks of threshold leve

variations of the possible trigger modes were made, max

the chance of catching an overvoltage, but indeed none oc

This unusual quiet was also reflected in the chart recording 

by the plant personnel, so that the absence of random tra

for that period can be accepted at face value. 

Therefore, conclusive evidence was obtained that sub

current pulses were absorbed by the varistors during ca

switching. The magnitude and duration of these pulse

excessive for the capability of a 20 mm disc; many similar 

installed elsewhere do not experience the failures encounte

that particular location. 

Another significant finding from these measurements 

fact that the switching transients, generated at the 23 kV 

propagate down to the point of utilization at the 460 V 

Numerical discussion of this finding is given later in this pap

Effect of Transients on Varistors 

Published varistor ~cifimtions inr!u& the "p&e ra!i

family of curves that define, for each varistor type, the num

isolated pulses that a varistor can absorb until its "ratin

reached i4i. The curves show lines relating amplitude, du

and total number of pulses. Figure 7 shows this family of 

for the original 20 mm varistor. 

Figure 8 shows the same curves for a proposed 32 mm 

tor. It should be noted that the pulse rating does not mea

strophic failure of the varistor at the end of this rating, but 

10% change in the varistor nominal voltage. Although 

change is indicated, the varistor is quite capable of staying 

voltage and of clamping surges. 

Figure 6. Capacitor switching transients 

lYCULSE 0UI)ATION - u 

Figure 7. Pulse ratings of 20 mm varistor 141 
e 1 l$:Z 

, 20.030 8 log 

4 xxa 

i lz 

Z m, 

100 3 50 

i? : 

5 

2 

20 50 100 200 500 1000 2000 SaaO 10.000 

IMPULSE DURATION -pa 

Figure 8. Pulse ratings of 32 mm varistor 151 

A careful examination of the pulse rating curves will show that 

the duration of the pulses has a strong influence on the number of 

permissible pulses. Furthermore, the relationship between the 

increased duration of the pulses and the decreased number of permissible pulses is not proportional. For instance, consider pulses 

of 106 A peak eiid 100 CLs (juia~oii (FigGFe 9A): the ci;ives 

5000 pulses allowed. Now increase the duration of the pulses to 

1000 ps (a ten-fold increase), while keeping the amplitude at 

100 A: the curves show the permissible number as one pulse 

only. Thus, the ten-fold increase in duration does not result in a 

ten-fold decrease in the number of permissible pulses; the reduction in that number is much greater than the inverse of the 

increase in duration. Conversely, taking a pulse duration of 

1000 ps, and seeking the amplitude allowable for the same 5000 

pulses, Figure 9B shows that the current is 20 A, which is five 

times less than the original 100 A, not ten times less. Therefore, 

it wou!d be incnrrect to treat the multiple pulses of Figure 5 as 

five separate short pulses; rather, one equivalent long pulse has to 

be defined. 

The five-pulse burst of Figure 5 has been redrawn in Figure 10 

in order to plot an equivalent continuous pulse of approximately 

equal duration, with a crest such that the i.t integral of the burst 

and the i.t of the equivalent pulse are approximately the same. 

The use of i.t rather than the i2.t integral typically used for fuses or 

other linear loads is justified by the fact that heat deposited in the 

varistors is the significant parameter because the nominal voltage 

change process is temperature related; this heat is the product of .L- -.--:^L1^ ^^A +a. ..-.... .. *n.."tnnt .,,,lto rtle vnjlavlr; i auu ue I,ral!j bu,,,,,,LL .,&.~ge acrass the non!inezr 

varistor during the burst. 

The equivalent pulse of Figure 10 can then be used to evaluate, from the pulse ratings of Figure 7, the number of highamplitude switching transients that will consume 100% of the 

vzris!~r pu!se rating. !nspec!lor? of Figure 6 shows that for a 

800 ps duration and 100 A amplitude, the pulse rating of the 

20 rnm varistor (6 kA rating at 8/20 ps) is reached with two such 

events. With a probability of about 10% that this highest switching 

transient would occur during random timing of the switching (the 

effect decreases rapidly for transients other than the highest) and 

with 2 to 4 swirching operaiions each day, iht piiise iatiiig of the 

varistors could be reached with 20 operations, failure perhaps 

starting at 40 to 50 operations, or after about 10 days of exposure 

to that power system environment. This estimate is unavoidably 

imprecise because the pulse rating curves represent a conservative 

minimum; actual failures will occur only for amplitudes or numbers of pulses exceeding the rating by a large but imprecise margin 

to allow for manufacturing variations. However, the order of 

magnitude of this estimated time to failure is in accord with the 

observations made at that installation. 

IMPULSE DURATION-p 

A. Same current, increasing duration 

20 I& I& 

IMPULSE DURATION-pa 

B. Same number of pulses, increasing duration 

Figure 9. Reading pulse ratings curves 

ACTUAL 

EQUIVALEN

Figure 10. Single-pulse equivalent pulse for multiple puls

Note that two types of events occur. One is the prema

blowing of the fuse, which is not caused by a varistor iaailure 

by the i2.t capacity of the fuse being exceeded by the environm

[I]. The other is the fuse blowing caused by the varistor end

life ultimate failure. 
Alternate Varistor Selection 

An obvious remedy would be to use a varistor with greater 

energy-handling capability. The 32 mm size offers such a possibility. Inspection of Figures 7 and 8 shows that the equivalent 

pulse of Figure 10 (800 ps and 100 A) corresponds to a permissible occurrence of 100 pulses for the 32 mm varistor, in contrast to 

the two for the 20 mm varistor. The improvement in the number 

of pulses is 50 times more pulses until pulse rating is reached. The 

improvement in the number of pulses until varistor failure occurs, 

however, is not necessarily 50 times more pulses. Because of the 

imprecision mentioned previously in the margin between end of 

pulse rating and ultimate failure, that margin is not necessarily the 

same for the two sizes, 20 mm and 32 mm, but it is reasonable to 

expect the same order of magnitude improvement in the ultimate 

failure as in the pulse rating. This expectation of a 50 times 

improvement would change !he time he!ween fal!ures frez the 

few days observed with the 20 mm size to perhaps one year with 

the 32 mm size, providing immediate relief and time to make fur- -. ther changes for the iong term. l'herefore, the change to a 32 mm 

size, connected c!t the saiiie ~kii of the circuit, was immadiaieiy 

implemented for that particular environment. 

Further gains could be obtained in the length of time between 

varistor failures by increasing the clamping voltage of the varistors. 

This increase would result in lower current pulses for the same 

open-circuit transient voltage. A 510 V rating had been selected 

by the designer of the drive as the result of a trade-off between 

varistor clamping voltage and the withstand voltage of the thyristors protected by the varistors. If thyristors with higher voltage 

withstand were used, the solution would be easy. 

Of course, the standard varistor product line has a certain tolerance band, reflecting normal production lot variations. In principle, a selection could be requested from the manufacturer that 

varistors with a narrower band be supplied for this application. 

The maximum clamping voltage allowed by the drive specifications 

would be retained, but those varistors in the lower half of the distribution, which draw larger current pulses for a given open-circuit 

transient voltage, would have been removed from the population 

01" varistors. For instance, the range of nominal voltages for a 

d c7C # d V, 32 m.?: ua:iatc: (the next higher vokage ofTered1 is 805 to 

1005 V for 1 mA dc, while the maximum nominal vo!tage of the 

same diameter but rated 510 V is 910 V for 1 mA dc. Thus, for a 

normal distribution of nominal voltages of the 575 V varistor, 50% 

of the devices could theoretically be used without exceeding the 

upper limit of the 510 V varistor that is consistent with the drive 

specifications. To achieve this end, it would be necessary for the 

supplier or user to make a careful determination of the nominal 

voltage on a population of 575 V varistors in order to retain only 

the lower half of the distribution (Figure 11). 

ACCEPTABLE LEVEL FOR THYRISTORS I 

SPECIFIED BY DRIVE DESIGNER 

PRESENT USE 

VOLTAGES FOR 510 V 910 

S FOR 575 V 805 I 1005 

Figure 11. Tolerances bands of 510 V 

and 575 V varistors 

Other Remedies 

In addition to the proposed upgrading of protecti

460 V level, three other remedies could be considered

tion of surge arresters at the 2300 V level, installation 

arresters at the 23 kV level, or a change in the circuits i

the capacitor switching, designed to reduce the sever

transients at their origin. 

In general, the protection available from surge arres

to improve when the arresters are installed at higher ci

ages. Thus, it is quite possible that arresters instal

2300 V primary of the 23001460 transformer could provi

effective clamping (and at the same time relieve som

energy stress) than the varistors at the 460 V level. 

course implied that these would be the zinc-oxide typ

arresters.) The full benefit of these arresters depend

conl?guration of the 2300 V system and its groundin

grounded iieiiirai iii a wye sysiem, resisiance-grounded 

Boating de!?a! when the Erresters are mnnected i~ th

tional line-to-ground mode. In a second phase of th

described here, 2300 V arresters were installed at the tr

primary. A discussion of their expected performance, va

the success of the retrofit, is given later on. 

Likewise, arresters on the 23 kV side could be insta

23 kV substation to mitigate the capacitor switching tra

their origin, or at the primary of the 23 kVl2300 V subst

the control house, where they would also serve as 

protection for the overhead 23 kV incoming power lin

arresters, again, must be of the gapless type to obtain 

effective protection. 

The final remedy in the list of alternatives, but perhap

in effectiveness when the opportunity exists, would be 

reducing the severity of the capacitor switching transien

origin. Series inductors or damping resistors may be c

the effectiveness of which would be predictable if a sim

the power system behavior were performed by comput

irSg. 'Wh.1- .. +h,,+ ----A., --.. IA --' L- ---*.-A ,Ar ruar tGILIeuJ Wuu IIUL VG aYY~icu io ihis p~ii

tion, it is a remedy that should be considered for n simi

exceptionally severe environment. 

&y,n,.mmr\ mmmmn..... .7.-." .." ---- ---- nrfiL1 ~u rfinrun~vmlr~c uri nr. LJUU V ARR

The measurements made first with open-circuit, then 

20 mm, 510 V varistors on the 460 V side have shown a 

of maximum voltage from 1450 V to 1100 V (Table 

current of approximately 200 A is flowing in the line an

(Figure 5). 

We can assume that the voltage drop in the line from 

tation and two step-down transformers is mostly in

5.5 kHz, and that the voltage in the varistors can be trea

voltage across a resistor at the time of the crest of t

wave. The diagram of Figure 12 shows the relationshi

the three voltages VoC, VL, and VV, respectively, the o

voltage generated by the capacitor switching action, t

drop in the line and two transformers, and the varistor 

the current peak. Treating this highly nonlinear circuit 

circuit is an appraximatinn !ha! ai!! pmvide P! each pe

full range of voltage and current conditions a valid order 

tude for the purposes of this discussion. Numerical m

avaiibie for rigorous treatment at any instant over the 

of conbi:Ioiis [6]. W-'L A'-- ----tP---- - niru r& sirrqmying assumpiion, we 

mine the order of magnitude of the 5.5 kHz current 

flow in an arrester installed at the primary terminals o

Vl460 V transformer as follows. 

REFERENCES 

F.D. Martzloff, "Matching Surge Protective Devices to their 

Environment," Proc. IEEE/IAS Meeting. October 1983, pp. 

387-392. (Also scheduled for IAS Transactions, Jan/Feb 

1985.) 

Committee. He is chairman of the Working Group on Surge Cha

zation in Low-Voltage Circuits. He is also a member of the A

Advisory Subcommittee of the USA Advisory Committee on IE

28A, ANSI C.62 Subcommittee on Low-Voltage Surge Pr

Devices, and Chairman of the NEMA Low-Voltage Arresters Te

Committee. He has been awarded 13 US. patents, primarily in t

of varistors and transient protection. 
Discussion 

J. L. Koepfinger (Duquesne Light Company, Pittsburgh, PA): The author 

has addressed one of many mechanisms for producing repetitive overvoltages on low-voltage circuits. In this partic& instance, ii was possible 

to obtain controlled conditions so that a measurement could be made 

of the voltage and currents resulting from the capacitor switching. It 

would be useful if there was an analytical method presented that cor- related the generation of the 5.5-kHz pulses with those measured. Did 

the author attempt to make such a correlation? 

This paper points out the need to know the characteristic of the surge so that proper sizing of the protection can be achieved. Therefore it would 

be desirable to be able to have some analytical tool to permit calculation of the frequency of the surge due to remote capacitor switching. 

Manuscript received July 24, 1985. 

Frnncois D. Martzloff: The paper reported a case history from which 

usefui informaiion may be derived on reirofiiiing correciions of simiiar 

pmb!ems or, he??er, on .voiding ?he pmh!em hy foresight. The d?lntions confronting the author was the need for immediate corrective action rather than complete investigation and mutual validation of analytical 

methods aid fieid measureiiieiits. 

The literature is fairly rich in both theoretical and practical papers on 

the ~roblems associated with ca~acitor switching, both for energizing 

andfor de-energizing, the latter involving the risi-of restrikes. B&U& 

of this availabilitv and the limited mace available in the mucno~s & one hand, andbecause of the limjtations in scope of the field retrofit 

mission on the other hand, no attempt was made to correlate the 

measurements with the power system parameters (which were not readily available to the author). In response to Mr. Koepfinger's suggestion, 

abstracts are cited below to provide references to both analytical tools 

and practical results published by other workers. 

Bibliography, 1970-1985 : REFERENCES 

[I] M. F. McGranaghan, W. E. Reid, S. W. Law, and D. W. Gresham, 

"Overvoltage Protection of Shunt-Capacitor Banks Using MOV Arresters," IEEE Trans. Power App. Syst., PAS-103, No. 8, Aug. 1984, 

pp. 2326-2333. 

Protection requirements and surge arrester duties are analyzed for 

boih digiiai and transient neiwork mdyzer (Tu'Aj shuiations. 3hp!c &n~n_a!pirA expressions are developed for evaluating arrester duty 

as a function of capacitor bank size. Guidelines and limitations for 

applying arresters at grounded- and ungrounded-wye capacitor banks 

ae deiieloued based oii overvokEge c~arac~er;spics &-ies;er 

capabilities. - 

121 - J. H. Brunke and G. G. Schoeckelt "Synchronous Energization of 

Shunt Capacitors at 230 kV," IEEE P& (Power Eng. sic.) Winter 

Meeting, New York, NY; Jan. 20-Feb. 3, 1978; Publ. by IEEE 1977, 

Paper A78-148-9, p. 4. 

This paper reports on the application of synchronous switching 

to reduce inrush transients when switching a 230-kV shunt capacitor 

bank. Computer studies determined the required switch performance. 

[3] J. D. Cuffman, John Linders, M. A. Zucker, and S. Willima , "Power Factor Correction Capacitors and Their Side Effects," IEEE 

Conf. Rec., 28th Ann. Conf. Electr. Ens. Probl. Rubber Plast. Ind., 

Akron, OH, April 5-6, 1976, pp. 37-49. 

The major reason for applying capacitors to an electrical distribution system is to correct poor power factor. In the greater majority 

of installtions it is a routine procedure. In some instances capacitors 

may cause problems with other in-plant equipment and in other instances they may suffer undesirable side effects that originate in other 

equipment. Among these problems are switching surges, voltage un- baiance due to fuses biowiiig, aiid iimiioiiics geiiergted by SCRcnn?m!!cd en,r?ipmen?= 

[4] H. J. Yelland, and C. P. Yellna, "Vacuum Contactors: Latest 

Development in Their Design and Application," Certif. Ens. V 54, 

No. 1. Jan. 1981, pp. 824-841. 

The paper includes the following topics: Design of vacuum bottles (glass and ceramic); design of the complete vacuum contactor 

and their panels; panels with on-load isolation, and panels with offload isolation vacuum contactor applications (motor con

capacitor switching, arc and other (furnace-switching, transfo

switching, mine-winder-reversers). Surge generation by vacuum 

tactors is considered under the following heads: basic energi

and de-energization transients; transients generated when swi

inductive loads; assessment of a vacuum contactor from a 

generation point of view; types of surge suppression devices; 

ching of capacitive loads. An extensive discussion of the pa

appended. 

[5] Jack R. Harbaugh and John E. Harder, "Important Consider

for Capacitor Applications in the Petroleum and Chemical Pr

Industries," IEEE Pet. Chem. Ind. Conf., 27th Ann. Rec. of C

Pap., Houston, TX, Sept. 8-10, 1980; IEEE, #80CH1549-5 

Piscataway. NJ, pp. 157-167. 

The location of capacitors may have a significant effect o

(I**2R losses within the plant transformers and conductors, w

is wasted energy. Transients generated by capacitor switching 

require attention in the selection of arresters, system insulatio

ofier equipmi. Ti ofcap&iors artly require som

attentinn to !&rge motors during system r=!&ng or tr&

This study addresses each of these considerations, providing 

guidelines for effective, reliable capacitor application. In add

a c:l&iisi is provided for iiidiiSiiid capaciior app&ai

[6] J. F. Burser, R. J. Santoro, J. W. Stolle. R. E. Owen and 

Clinkenbeard, "Comparative Evaluation of Field Test Data 

Computer Results on Capacitor Switching Transients." Me

Minutes PA Electr. Assoc., Eng. Sect., Trans. and Distrb. Co

West Middlesec, PA, May 15-16,1979; PAElectr. Assoc., Eng. 

Harrisburg, PA 1979. 

An arrester failure case was analyzed occurring at the tim

substation capacitor bank switching with the use of a transien

work analyzer (TNA) and digital computer techniques. The ca

volved a 12.5-kV ground-wye distribution sytem. Results of the 

study, which were validated by field tests, showed the effects of s

configuration magnitude of transient over voltages. 

[7] Eldon J. Rosers, and Don A. Gilles, "Shunt Capacitor Swit

EM1 Voltages, Their Reduction in Bonneville Power Administr

Substations," IEEE Trans. Power Appar. Syst. PAS-93, N

Nov.-Dec. 1974, pp. 1849-1860. 

Back-to-back switching of grounded wye shunt capacitors 

high frequency, high-magnitude current flow in overhead bu

___..->___. .,___.______,?I->..___I___,.___

~~UUIIU mat WIIUUSLU~S. IVLS~SU~CIIICIILS UL IIIUUSCU vu~tagcs UI

trol cables and receptacles; transverse voltages on fuse blow

secondaries and personnel intercept voltages are reported. 

methods of confining transients to capacitor areas and shie

*--I.-: --..:-.*."a LGcIlluqusJ as Isvlswsu. 

[8] Paul C. Krause and William C. Mauser, "On-Line Transient 

trol of Capacitor Switching to Improve System Stability," 

Trans. Power Appar. Syst. PAS-92, No. 1, Jan-Feb. 1973

321-329. 

A simplified voltage-reactance equivalent of the one-machi

fhte bus system was used. The material presented in this paper 

that this simplified model does not predict the performance of a 

machine infinite bus system with the accuracy necessary to dete

the capacitor switching times so as to achieve the control objec

However, it is shown that computation accuracy may be imp

by including system losses. It appears that in order to apply op

control techniques it will be necessary to develop more acc

models of the power system components. Also, faster than rea

iterative, on-line computation techniques as simulated in this 

should be implemented and used to calculate the switching t

Until these obstacles are overcome, optimal control theory will 

little impact upon the power industry. 

[9] D. 0. Wiitanen, J. D. Morgan, and G. L. Gaibrois, "St

Tr _--- :I-- "...1.-LI-_ IF_--^:^-*^ 1- -,..I-, --A r?..-^-:-^

uqxutul JWILSIIIII~ I I iulwslrLa, fulayrrcal 611u LA~~L

Results;" IEEE Trans. PowerApp. Syst. PAS-90, No. 4; July-

1971, pp. 1639-1645. 

Station capacitor bank energization transients predicted by 

cuit model are compared to field-test results. Selection of a su

model is discussed. A computer solution of the model is prese

Manuscript received September 19, 1985.