AJWG-77B(Martzloff/Geneva)l 

November 1994 

International Electrotechnical Commission 

Technical Committee 77 - Electromagnetic Compatibility 

Subcommittee 778 - High-Frequency Phenomena 

Contribution to: Joint Working Group "Surge Overvoltages and Surge Protection" 

From: Fran~ois D. Martzloff 

Overvoltage protection: Principles, postulates and perceptions 

1. Rationale 

As our Joint Working Group begins its assigned task, it seems appropriate to take a look at where we are 

now and where we want to be a few years (not too manyl) from now in our knowledge of how to control 

overvoltages in a safe, technically sound, and cost-effective manner. This paper is being circulated to the 

Group before the meeting to promote a faster start and quicker consensus building when we meet around 

the table. 

Several of the papers reviewed in an Annotated Bibliography on Cascade Coordination started in 1992 

(enclosed) are based on assumed basic parameters that affect the outcome of a coordinated cascade of 

surge-protective devices (SPDs) in low-voltage end-user systems. Consequently, and it should be no 

surprise, the conclusions presented by the different authors are sometimes different. Some of these 

parameters represent a postulate on the environment, over which we have no control. Other parameters 

result from installation practices over which we have little control, given the existing installations and the 

present standards that govern them. Finally, even the selection process of SPDs, over which we should 

have a good measure of control, is in fact uncontrolled in an unregulated marketplace where end-users lack 

dependable information. 

Lest we meet and work to discuss the technical problems and reach contradictory conclusions resulting 

from different postulates or perceptions, we need to agree on these parameters to carry on a meaningful 

discussion in our quest for a technically valid solution. Preparing effective recommendations for the 

control of overvoltages (also known as surge protection, lightning protection, disturbance mitigation, 

insulation coordination ...I requires judicious application of the fundamental principles known to us and use 

of available tools, for the ultimate goal of dealing with the reality of overvoltages as they occur in our 

systems. In recent years, one of the concepts initially proposed by IEC Pub 664, namely the existence of 

a down-staircase of voltages, has come into question. Work on SPD cascade coordination clearly shows 

the pitfall of that concept, and research on the propagation of surge voltages casts a serious doubt on the 

likelihood of a natural reduction of voltage surge amplitudes as they propagate from the service entrance 

to the end of the branch circuits. 

Our discussions are likely to address four aspects of the problem: what is occurring in the real world; what 

we can simulate and measure with discrete components in the laboratory; what we can simulate and 

compute with a numerical model; and finally, what protection industry can provide at a price that end-users 

are willing to pay. It is not evident that all four aspects use a common foundation of compatible 

postulates. There seems to be as many unanswered questions as unquestioned answers that might 

sidetrack us, literally, while our objective should be to go forward (Figure 1). 

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figure 7 - The choice is ours ! 

The diversity of our professional and technical experiences is likely to give each of us a different 

perspective on the technical and economic problem we are attempting to solve. In fact, this diversity will 

be an asset in our work if we can start by identifying the unanswered questions and, at the outset, reopen 

the unquestioned answers, treating them all alike. 

Therefore, the following questions are proposed for consideration as possible initial topics of consensusbuilding. Agreeing on perspectives and goals now will avoid misunderstandings later, as well as preventing 

circular discussions in our work. Some of these questions might seem trivial, or their answers obvious, 

but raising them in the form of a check list, presented at the end of this paper, might still be useful to focus 

our discussions. For the sake of starting the review and discussion, the questions are listed according to 

the four aspects cited in the Rationale above. This organization may readily be modified as the AJWG 

contributors might propose other structures and identify important questions that may have been 

overlooked in the present paper. 

2. What is occurring in the real world ? 

We have several sources of information available, as listed below, on what the surge environment is in the 

real world of low-voltage systems. Other members of the AJWG most probably have other sources known 

to them, so that pooling these sources may be a task for the AJWG to undertake or to delegate. 

2.1 Direct observation of overvoltages 

Without going back to Benjamin Franklin's days, many researchers have conducted surveys and 

measurements to quantify the threat of overvoltages. These have been along two main categories: One 

is the direct measurement of the phenomenon near its source, such as the lightning stroke (passive 

monitoring on selected sites, or triggered discharges through an instrumented path), a capacitor switching 

event, a fuse-blowing occurrence, a contactor bounce, etc. The other category is the monitoring of 

overvoltages in the end-user system, mostly in low-voltage ac power systems at the point of common 

coupling or at the point of use. The literature' also contains reports of measurements in telephone systems 

and in medium-voltage ac distribution systems. Progress in instrumentation is remarkable, starting with 

Liechtenstein figures on film, magnetized link detectors, threshold counters, oscilloscope-camera 

combinations, and now digitizing instruments with on-board data processing capability and textlgraphics 

output. 

1 This paper being a discussion-starter and not an academic-type treatise, no references are listed at 

this stage. Depending on the wishes of the AJWG, a list of references may be compiled as a joint effort. 

In the meantime, the absence of references should not be seen as ignoring the many 

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contributors to the field. 

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A serious difficulty has surfaced in comparing and consolidating results: each researcher used different 

criteria or thresholds to define and accept in the data base what is then reported as a significant event. 

For instance two widely cited surveys, Goldstein & Speranza used for their threshold the values above 

which telephone equipment might be disrupted, while Allen & Segall used computer disturbance thresholds 

as their criteria. Another limitation of these monitoring campaigns in end-user systems is that most have 

been limited to the measurement of a voltage. Very few included a current measurement. This limitation, 

however, has not stopped some authors from computing the time-integral of the square of the voltage, 

dividing it by some impedance and calling the result "energy in the surge", offering that result expressed 

in joules as guidance for the selection of an SPD I The reality is that a non-linear SPD inserted in the loop 

formed by the surge source, the transmission line, and the SPD cannot be equated to the linear 

configuration assumed when computing the energy dissipated in a resistive load. Not knowing the 

complete circuit parameters, the energy that would be deposited in an SPD connected at the point of 

measurement cannot be determined from the voltage measurement alone. 

There is no agreement, perhaps even little understanding, on how a surge event should be viewed: is it a 

voltage source that is fed by a transmission line to the equipment, is it a current source, or is it a discrete 

amount of energy injected into the power system? Depending upon the answer to these questions, 

different scenarios will be written for describing how a surge of several thousand amperes can propagate 

through a 277-ohm or 400-ohm "transmission line" insulated for low-voltage characteristics, how the line 

should be viewed (distributed or lumped elements), and many other questions or apparent contradictions. 

With more information provided on these assumptions, these apparent contradictions might then be 

resolved into simple explanations. 

Would it be beneficial to the process that the AJWG compile an up-to-date bibliography of the many 

published surveys, and attempt to secure advance information on those surveys currently in progress here 

and there? Is such an undertaking already in progress somewhere in the IEC or in some other organization7 

2.2 Theoretical analyses 

Physicists have conducted analyses of the lightning discharge phenomenon, engineers have computed the 

parameters of switching surges, all in an effort to predict and quantify the result of a phenomenon which 

cannot be readily duplicated in the laboratory. In some instances, however. it has been possible to 

conduct some experimental work in conjunction with the theoretical analysis and thus to validate the 

process. 

2.3 Using field failures as a monitor of overvoltages 

Manufacturers typically are reluctant to give broad publicity to the failure of their products, and most field 

failures are reported by users or their consultants. This situation is not ideal as some bias may occur in 

the process. This is unfortunate, as field experience is the ultimate validation of all theories and design, 

and very convincing evidence could be gathered through this channel. Examples of such data include: a 

case history of clock redesign to 6 kV withstand following widespread failure for a 2 kV withstand, 

producing a 100:l reduction in the failure rate; the fact that most 120-V rated incandescent light bulbs 

flashover and burn their filament with surges above 1.5 kV but still achieve an acceptable life in use; the 

fact that millions of varistors installed in equipment do not fail in the field but fail in the laboratory when 

exposed to a long-duration surge proposed in the IEC Standard 1000-4-1 menu. 

2.4 Agreeing on a limited set of parameters 

Here again, a pooling of such field experience among the members of the AJWG would be a strong factor 

toward building credibility for proposed "representative waveforms" that SPDs should be capable of dealing 

with. There is a tendency among standards writers to specify test waveforms that duplicate as closely 

as possible what is happening in the real world, a commendable goal, but resulting in a proliferation of 

"standard waveforms". In a 1987 paper, Frey tabulated 95 (ninety-five !) standards calling for 

One common would-be humorous poster found in metrology laboratories states: 'The nice thing about 

standards is that there are so many of them. that you can choose the one that best suits you I' 

Actually, this is a rather dark and sad commentaw on the state of international and national 

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standards. 

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"representative waveforms". Thus, one of the first tasks of the AJWG is likely to be the challenge of 

achieving a consensus on what parameters (waveform, amplitude, source impedance, frequency or 

probability of occurrence ... ) should be considered in our work. 

3. What can we simulate and measure with discrete components in the laboratory ? 

Laboratory work on surge protective devices and protection of equipment is generally conducted on fullscale equipment if possible, or on sub-assemblies if the full-scale is impractical. The surge is obtained from 

home-made or commercial generators. The goal is sometimes perceived as a demonstration that the 

equipment will be immune to real-world threats. Actually, and this may sound trivial or obvious but is often 

forgotten: all the test has demonstrated is that the equipment has survived the test. An important aspect 

of that procedure is to ensure that comparisons can be made within one laboratory between tests 

performed on different designs or at different times, and that comparisons among laboratories are 

meaningful. This fact alone is sufficient to demand agreement on standard procedures and standard 

surges. Some occurrences have been noted that test generators built by different organizations, each in 

accordance with the specifications of a particular standard, may in fact produce different stresses. Careful 

standards writers address that problem through systematic round-robin test programs. Researchers 

attempt to prevent the problem by inviting peers to corroborate their results. Thus, one task of our 

coordination working group may be to catalyze such round-robin tests and corroboration of results. 

The type of surge generator used in different laboratories, or among different groups of users, is also a 

subject that our AJWG should consider. The question surfaced during the Florence meeting of two years 

ago, even though the agenda did not allow for indepth discussion. Depending upon the assumptions made 

on the real-world threat, the surge generator may be viewed as a voltage source, a current source, or a 

hybrid source. 

From years of testing for insulation withstand, many laboratories have developed the mental habit of 

testing with voltage waveforms, without much concern about the impedance of the generator as long as 

the specified voltage could be maintained across the test piece. Surge arrester people, on the other hand, 

were equally concerned with the response of an arrester to a voltage front and to a discharge current, but 

they generally separated the two aspects in different tests. Low-voltage electronics users and 

manufacturers developed the concept of a hybrid generator to test the response of a given equipment to 

its environment. 

One result of bringing these different points of view to the same laboratory is the attempt to modify a 

surge generator designed for one assumption so that it can also be used to perform a test for another set 

of assumptions. For instance, a generally accepted internal impedance value for a hybrid (a.k.a. 

Combination Wave) generator is 2 ohms. Other suggested values have been 10 or 12 ohms, 50 ohms, 400 

ohms ... The next thing that happens is that an external resistor is being inserted in the test circuit, losing 

sight of the fact that the "2 ohms" is in fact the ratio of the peak open-circuit voltage and peak shortcircuit current (which occur neither concurrently -- they are mutually exclusive -- nor at the same time of 

the event), and while it might have the dimension of ohms, calling it internal impedance is an 

oversimplification; a reminder would be to call it 'effective impedance'. 

Measurements made with modern instruments pose few problems. Industrial laboratories are staffed with 

competent personnel and few artifacts escape detection. In fact, producing test records has become so 

easy that one can be easily drowned in test data. A challenge is then to unify laboratory results and the 

conclusions that can be drawn from the overabundance of laboratory data. This challenge may be beyond 

the scope or capability of the resources available to the AJWG members, but it is worth noting. 

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4. What can we simulate and compute with a numerical model ? 

Numerical modeling has gained popularity as software packages have become readily available, 

supplementing the analyses initially limited to main-frame computers, including classical codes such as 

EMTP. However, the very availability of many computer programs has produced a flurry of studies which 

are not readily comparable. For instance, Martzloff persuaded different experts on computing methods 

to contribute to several surge-related investigations: given the freedom to do so, each computing expert 

chose a different model to simulate the source of the surge, its propagation in the circuit, and the response 

of the circuit or device under test. Is such a diversity useful in demonstrating the flexibility of the 

approach, or is it counterproductive by making comparisons among experts more difficult? Should the 

AJWG promote the use of a particular code, without falling into the trap of restricting the freedom of 

researchers? 

__C___ In these investigations, reasonable agreement has been found between experimental and modeling results 

when both were conducted, but some discomfort lingers about the need and justification of applying scarce 

resources to recreate a model for each investigation. Another lingering discomfort when attempting a 

computer modeling project is rooted in the simplifications that must be made to the equivalent circuit so 

that the program can be handled by the computer. Members of the AJWG with more experience on 

modeling techniques, or access to modeling/computing experts might consider some work aimed at 

catalyzing the use of only a few, well recognized and user-friendly computer codes. The quest for 

improvements and originality so inherent in motivated researchers should be balanced against the desirable 

cost-effectiveness and easier consensus obtained with stable, well-accepted modeling methods. 

hb3vhat can industry provide at a price that end-users are willing to pay ? 

Under development - major themes: - statistical aspects of threat 

- statistical aspects of equipment withstand 

- classification of environmentlusers 

- type of mission (consequences of failures) 

6. Quo vadis 7 

The final question raised in this position paper is meant as a gentle reminder to the AJWG. We should 

structure our work, discussions, and ultimately preparation of useful documents based on a pragmatic 

recognition that while an ideal situation may be designed and even proposed as a mandatory standard, 

acceptance of such recommendations by industry is the ultimate criterion of a successful undertaking. We 

should not indulge in a quest for perfection, but seek out solutions that can be implemented in the short 

term, perhaps with some directions given for the long term if they have a reasonable likelihood of 

acceptance. Hopefully, this position paper might he!:, toward that objective. 

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CHECK LIST 

What is occurring in the real world ? 

- What information does each member of the AJWG have on surge occurrences? 

- Should the AJWG prepare a (annotated) bibliography? 

- For its own use in developing documents 

- As a service to other IEC groups 

- Can the AJWG propose a generally acceptable, limited set of threats? 

- Lightning 

- Normal switching operations 

- Fault clearing 

- Others 

- Other questions from the AJWG: 

What can we simulate and measure with discrete components in the laboratory ? 

- Select a current, voltage, or hybrid source, according to the origin of the threat? 

- Is there agreement on waveforms? 

- Other questions from the AJWG: 

What can we simulate and compute with a numerical model ? 

- What models are available for a varistor? 

- What models are available for a gap? 

- What models are available for the threat source? 

- What model should be selected for the wiring system? 

- Is there a preferred approach to be recommended to others? 

- Other questions from the AJWG: 

What can industry provide at a price that end-users are willing to pay ? 

- Statistical aspects of the threat 

- Statistical aspects of equipment withstand 

- Classification of environmentlusersllocations 

- Type of mission (consequences of failures) 

- Other questions from the AJWG: 

Quo vadis ? 

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