Charles Fenimore and François Martzloff

National Institute of Standards and Technology

Gaithersburg MD 20899 USA

f.martzloff@ieee.org

Reprinted, with permission, from 

Proceedings, 9th International Zürich Symposium on Electromagnetic Compatibility, 1991

Significance:

Part 2 – Development of standards – Reality checks

Demonstration ad absurdum: 

Accepting the premise of prevalent 100/1300 high-energy surges and modeling the response of typical metal-oxide

varistors leads to the conclusion that most of the billions of varistors in service should fail at alarming rates – but

we know they do not. Ergo, the premise is not valid. 

This paper was part of a successful effort to discourage the IEC TC77 from including that 100/1300 test in the

regimen of across-the board EMC testing.

(See also paper “MOV - VDE" in this Part 2 for an experimental demonstration.)

Filename: Incompatibility
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is based, a ready calculation using the capacitively 

stored energy, q2/2C (of order 5000 J), shows that 

no more than 10% of the stored energy is spent in 

the MOV in the simulations according to the two approaches discussed above. Yet, these two tests are 

aiready destructive or' the device. it seems likely 'chat 

a test that would meet the 80% criterion would provide an even more severe stress to the equipment, and 

provide a greater disparity between the model results 

and field experience. 

Thus, the authors suggest that a reexamination of the 

premises that led to the VDE 0160 Standard should 

be considered before incorporating a blanket requirement for such a test into new IEC surge immunity 

standards. The authors plan to perform actual tests 

on typical varistors to further support the computations presented in this paper. 

CONCLUSIONS 

1. A mathematical and derived computational model 

has been presented which permits the evaluation of 

many aspects of varistor performance over a range of 

conditions which are characteristic of the actual operating environment and also of the test environment 

contemplated by VDE 0160 and other surge standards. 

2. Computer model predictions of the impact of the 

proposed 100/1300ps surge test on the millions of 

varistors in service shows that these varistors should 

experience a greater failure rate than indicated by 

available information on actual failures. The simplified inductance-free model provides analytical confirmation of this result. This inconsistency raises serious 

questions on the proposed requirement of such a severe test to a wide range of equipment. 

3. The lingering ambiguity on setting a constant opencircuit voltage or adjusting the voitage whiie the specimen is connected needs to be clarified. A constant 

open-circuit voltage is the generally accepted practice in surge testing. The premises that led to this 

new surge test may justify adjusting the charging voltage after the test specimen has been connected to the 

surge generator; that adjustment, however, results in 

larger amounts of energy being dissipated in surge protective devices, making the apparent incompatibility 

identified above even greater. 

4. The criterion that 80% of the capacitive energy 

must be transferred to the test specimen may be difficult to satisfy and needs clarification. The authors 

have been unable to identify a simple circuit which 

satisfies the criterion while maintaining the required 

rate of decay under open circuit conditions. 

5. While the authors do not question the validi

the fuse-blowing scenario, they recommend a cri

review of the statistics of the occurrence of fuse h

ing, of the use of varistors with low clarnping 

age, and of the distribution of actual clamping 

age within manufacturing tolerances. Tile serisii

model developed in this paper may be a uscful 

in evaluating the effect of these tolerances. Th

thors also urge all users to share infornlat,ion on 

observed failure rates, as well as to perform val

ing tests, in order to provide a broader perspectiv

these issues. 

REFERENCES ' 

IEC Document 77B(Central Office)4, Overvie

Electromagnetic Compatibility - Immunity T

MEISSEN, W., ~berspannun~en i Niedcrs

nungsnetzen, Elektrotechnische Zeitschrift, , vo

1983. 

VDE 0160 Ausriistung von Starkstrornanlagc

elektronischen Betriebsmitteln, May 1988. 

quotations appearing in this paper from the te

this standard are made from the oficial En

translation available from the British Standard

stitution). 

VDE Ol6OAl ~nderun~ 1 zu DIN VDE 0160/0

April 1989. 

MEISSEN, W., Private communication, 1990

WEISINGER, J., Hybrid-Generator fiir dic 

lationskoordination, Elektrotechniscl~e Zeitsc

vol. 104, 1983. 

ANSIIIEEE C62.45-1987, Guide on Surge 

ing for Equipment Connected to Low-Voltag

Power Circuits. 

MARTZLOFF, F.D. and LEEDY, T.E., Selc

Varistor Clamping Voltage: Lower is not Be

Proceedings, 1989 Ziirich EMC Symposium. 

Transient Voltage Suppression Devices, HA

CORP., Somerville, NJ, USA, 1990. 

E. ARGON, I.L. CHANG, G. GUNARATRA

KAHANER, and M. A. REED, "Mathematica

ware: PLOD," IEEE Micro, vol. 8 (4), August 

I ~ertain - sofiware is identified in ihis paper in order t

equately specify the procedures used to produce the num

results. Such identification does not imply thit the softw

necessarily the best available for the purpose. 
.