what went on in the realworld surge environment. 

This need for changing from voltage to surge current monitoring was addressed in several other papers 

presented on both sides of the Atlantic (See in Part 5 “No joules,” 1996; Make sense,” 1996; “Joules YesNo,” 1997; “Novel transducer,” 2000; and “Galore,” 1999 in Part 2), in persistent but unsuccessful 

attempts to persuade manufacturers and users of power quality monitors, and standards-developing 

groups concerned with power quality measurements to address the fallacy of continuing to monitor surge 

voltages in post-1980 power distribution systems As it turned out, the response has been polite interest 

but no decisive action. 

The proposal to gather field failure data also met with little enthusiasm at the time, however more recent 

standard-development activities indicate a possibility that the idea might not be completely abandoned.
KEEPING UP WITH THE REALITY OF TODAY'S SURGE ENVIRONMENT 

Fran~ois D. Martzloff 

ational Institute of Standards and Technology * 

Gaithersburg, Maryland 20899 

Abstrac establish a program for characterizing surge events by the capability of a surge 

event to deliver a surge current through the power system in end-user facilities. This characterization would 

complement or even supersede the conventional monitoring of surge voltages. Two approaches are suggested: 

(1) Using a metal-oxide varistor with the lowest possible voltage to "attract" surges away from other SPDs 

connected in the facility, and then recording the surge current waveform in the varistor; (2) Gathering data on 

field failures attributable to surges or swells for all types of electrical appliances, then attempting to replicate the 

failure mode in the laboratory. 

HISTORY 

Characterizing the surge environment has been a subject of research for the last forty years, driven 

by the increasing concern about the vulnerability of new electronic appliances to transient 

overvoltages. However, practically all the recording campaigns conducted by major organizations 

such as Bell (Goldstein and Speranza, 1992)[1], Canadian Electrical Association (Hughes and Chan, 

1995)[2], General Electric (Martzloff and Hahn, 1970)[3], IBM (Allen & Segall, 1974)[4], National 

Power Laboratory (Dorr, 1995)[5] and other researchers, including Forti and Millanta, 1990 [6], 

Goedbloed, 1987 [7], Hassler and Lagadec, 1979 [8], Meissen, 1983 [9], and Standler, 1989 [lo] 

have been limited to the measurements of transient voltages. This focus on transient voltages was 

initially justified for two reasons: (1) the emphasis was on concerns of equipment failure subjected 

to overvoltages in the absence of adequate protection, and (2) shunt-connecting a voltage sensor to 

a power circuit is easier than inserting a current sensor in series with the lines. 

The idea of recording surge currents that could be "attracted" by a surge-protective device (SPD) 

with the lowest clamping voltage in an installation was suggested in the discussion of a paper 

describing a digital instrument with current-recording capability (Odenberg and Braskich, 1985)[1 I]. 

A recording system with capability of recording both current and voltage, using oscilloscopes and 

digitizers, was developed and described in (Standler, 1987)[12]. These two recording systems were 

developed before the explosion, in the mid-eighties, of power quality monitoring projects made 

possible by the commercial availability of portable monitors with graphics capability. An ongoing 

project for monitoring power quality in the medium-voltage distribution systems (not low-voltage 

end-user systems), sponsored by the Electric Power Research Institute, is based on an instrument 

which has a limited response at the frequency range associated with surge voltages. 

With the benefit of hindsight, this paper proposes a change in the way power quality monitoring 

projects are conducted. The emphasis would be shifted from recording transient voltages, or surge 

voltages, to the determination of what surge currents may be delivered by a surge event to a surgeprotective device. This shift is necessary because a new situation has arisen in the surge environment. 

* Elech-ici~ Division, Electronics and Electrical Engineering Laboratory, Technology Administration, US. Department of 

Commerce. Contributions from the National Institute of Standards and Technology are not protected by US. Copyright. 

246 POWER QUALITY SOLUTlONS SEPTEMBER 1995 PROCEEDINGS 
THE NEW SURGE ENVIRONMENT 

In spite of the proposals cited above for recording surge currents that could be delivered to a 

candidate SPD, the idea has not caught on and recording surge voltages still seems to be the order 

of the day. In the last few years, following the advent of the metal-oxide varistor protective devices, 

the actual situation concerning observation of transient overvoltages has become quite different. 

These devices are now so ubiquitous (an estimated number of installed varistors in the United States 

is two billion) that hardly any location can be found where there is not some form of transient voltage 

limitation in effect*. Nonetheless, proposals are still being made, and in some cases implemented, 

to continue monitoring transient oven~oltqp exclusively inside end-user facilities, in a noble attempt 

to characterize the environment so that appropriate surge-protective devices could then be prescribed 

for specific locations. What this measurement yields, however, is no longer the surge characteristic 

of the monitored system, but the residual voltage of whatever SPDs are installed nearby. 

Thus, the results of any measurement campaign conducted in the future and limited to voltage 

transients will be totally irrelevant, worse yet, misleading. Such measurements will provide a false 

sense of security based on the uncontrolled presence of undefined surge-protective devices. The 

results might lead to the erroneous conclusion that the surge environment being monitored is benign 

(Aspnes et al., 1985)[13]. But this might not be the case; for instance if a user were to install an SPD 

with clamping voltage and current-handling capability lower than those of SPDs already in place, the 

newly installed SPD would then "attract" incoming surges. These surges, in turn, might have a 

current-delivery capability beyond the limited capacity of the new SPD. Although such a situation 

might be rare, it would be an unpleasant surprise to the unwary end-user. To draw a parallel, the 

practice of deriving surge-current protection schemes from the measurement of surge voltages in the 

presence of unknown SPDs is akin to deriving power-frequency fault-current protection from voltage 

measurements made during a fault, rather than applying the well-developed overcurrent coordination 

practice used by power system engineers. 

A recent draft document proposed for monitoring Power Quality mistakenly included the 

characterization of "the energy in the surges" by making measurements only of voltage as a hnction 

of time, integrating the square of the voltage, and dividing the result by an arbitrary resistance, such 

as the characteristic impedance of the wiring. The basis for this approach may have been rooted in 

the fact that in the past (mid-eighties), disturbance monitors did print out results labeled as "joules." 

However, regardless of the source, practices based on this misconception have now been recognized 

as erroneous and have been discontinued. Recognition should be given to Goedbloed's work, 

previously cited, in which he created the term "energy measure" to assess a parameter involving the 

integral of the voltage square as a usefbl way of obtaining some information on the strength of a surge 

event, but he avoided the pitfall of presenting the concept in terms ofjoules. 

- 

* An often-cited document, ANSIAEEE C62.4 1, Recommended Practices on Surge Voltages in AC Power 

Circuits, provides in graphical form a description of the frequency of occurrences vs. peak values of the 

surges at unprotectedlocations. This specification of unprotected locations still reflects the only available 

data base and the mind-set of users concerned with the need for adding surge protection in an installation 

where none is provided -- which is no longer the present situation. 

POWER QUALITY SOLUTIONS SEPTEMBER 1995 PROCEEDINGS 247 
A NEW APPROACH FOR MEASUREMENT OR 

INDIRECT ASSESSMENT OF SURGE CURRENTS 

In contrast to the traditional and potentially misleading recording of surge voltages, a change to 

measuring or at least indirectly assessing the surge current (both magnitude and waveform or 

duration) would provide more meanin&] information on today's surge environment. Two ideas for 

obtaining that type of information are described in this paper. The first idea is based on installing a 

varistor with very low clamping voltage and recording the current drawn by that varistor. This 

approach would yield new and detailed information based on actual surge-current measurements. A 

second approach would use field-failure data from appliances such as packaged SPDs or light bulbs 

combined with a laboratory replication of their failure modes. This replication would allow credible 

conjectures on the field conditions that led to the failure of the appliances. The outcome of this 

second approach would yield a statistical upper bound on the magnitude and frequency occurrence 

of surges with high energy-delivery capability. 

First approach: Direct measurement of available surge currents 

In this first approach, an SPD with the minimum tolerable voltage rating across the power line would 

be connected at various points of an installation, one location at a time, to serve as a "magnet" 

attracting the impinging surges. This SPD would be specially sized and well-characterized to ensure 

the "magnet" function of drawing most of the available surge current. 

Two limitations have to be recognized in this approach. The first is the requirement that the SPD 

operates on the brink ofdrawing excessive standby current with the line voltage at its upper practical 

range. The second is the potential impact of other SPDs located upstream of the "magnet." These 

other SPDs would compete in attracting the available surge current, because of their connection in 

the so-called "cascade" arrangement (Martzloff and Lai, 1992)[14]. A "calibrated" SPD could be 

designed by NIST in cooperation with varistor manufacturers to provide the necessary characteristics 

of low clamping voltage, on the secure side of the brink. The surge current attracted by the varistor 

could then be recorded to find the true character of surge events at that location, despite the presence 

in the local system of any unknown and uncontrolled SPDs. 

In a first implementation of this idea, the surge current would be recorded by using the current probe 

that is a common accessory of the various types of commercial power quality monitors owned or 

operated by hundreds of organizations and researchers. However, the frequency response of these 

current probes might not be appropriate for recording surge currents. A modified approach is now 

being investigated, using a current transformer with a higher frequency response. The output of the 

transformer, with an appropriate burden, is then fed to the voltage channel of the monitor, which has 

a better frequency response than the current-probe channel. The combination of the calibrated 

varistor, current transformer, and burden serves as a transducer converting the surge current into a 

voltage signal readily acceptable to existing power quality rrionitors. 

In its elementary concept, this current-measurement approach will readily produce a spectrum of 

current surges describing the environment at the point of connection of the varistor. However, 

turning this local spectrum into a broad data base will require some information processing to take 

248 POWER QUALITY SOLUTIONS SEPTEMBER 1995 PROCEEDINGS 
into consideration local conditions. These conditions might include the structure and ratings of the 

power supply system from the distribution transformer and downstream, the presence of a surge 

arrester on the primary of the transformer, local ground resistivity, etc. The results of the "UpsideDown House" modeling (Martzloff et al., 1995)[15] could be applied to determine how far 

downstream the low-voltage SPD can remain an effective and calibrated "magnet" of the available 

surge when other SPDs are present in the system. In this manner, one could characterize the strength 

of the surge event, shaped by the local power system, to deliver a surge current. In turn, this 

knowledge would allow prediction of the amount of energy that would be deposited in any candidate 

SPD, a factor which is presently unknown. By using two separate channels (high-frequency and 

60-Hz responses, with appropriate sensitivity level) of the commercial monitor while recording the 

current drawn by the varistor, it will be possible to characterize swells as well as surges, increasing 

the information yield of the project. 

Selecting the specially sized SPD at the brink, as discussed above, entails a definite probability that 

its rating will be exceeded under some circumstances, so that the varistor must be considered as 

expendable. A suitable overcurrent protection must then be provided in series with the varistor to 

clear the resulting short-circuit. To provide continued monitoring, several varistors could be 

connected in parallel, each with a fuse, in a "staircase7' of incremental voltages to allow several stages 

of recording before all devices are consumed. This idea is now being explored, but first indications 

are that varistors will have to be very closely characterized to ensure this staircase of clamping 

voltages. For instance, characterizing the varistors by their nominal voltage (voltage at 1 mA DC) 

to select different voltages for the staircase does not necessarily ensure that the same difference will 

be maintained at higher levels of surge currents. 

The ability to replace the expendable varistors would be essential if the staircase approach turns out 

to be impractical. A completely expendable transducer box -- including calibrated varistor(s), fkse(s), 

current transformer, and burden -- might not be practical in view of the investment necessary for the 

current transformer contained in the box. The SPDs could be enclosed in a safety-approved 

enclosure, with provision for replacing a failed SPD and its fkse, allowing the operator to resume 

monitoring. However, the need to open the box and replace components might be a deterrent to 

widespread acceptance. Success of the project would depend on recruiting researchers committed 

to obtaining this new type of data. An unresolved question at this stage is whether or not an approval 

by Underwriters Laboratories or some other agency would be necessary to make the transducer box 

acceptable for widespread connection to end-user facilities. Assuming that this suggestion receives 

encouragement from the engineering community, resolving these specific questions will be the next 

phase of the project. 

Second approach: Replicating field failures 

In this approach, failed appliances created in the laboratory would be compared to the appearance 

of failed appliances returned by end-users. A reasonable leap of faith is implied in this process that 

indeed the two failures resulted from similar surge (or swell) events. The conclusion would then be 

an experience-based assessment of the occurrence of such events at the failure level observed in the 

laboratory for the same appliance. 

POWER QUALITY SOLUTIONS SEPTEMBER 1995 PROCEEDINGS 249 
Some may point out all the factors that could make this leap of faith unreliable, conhsing, misleading, 

etc. In fact, it is the very purpose of this paper to expose the idea so that the potential difficulties can 

be identified and hopehlly dealt with by carehl analysis of the data. This paper is presented as an 

invitation to colleagues and commercial organizations interested in a cooperative effort of sharing 

field failure data. 

SPD field failure data 

Manufacturers of packaged SPDs who accept or invite the return of SPDs that failed in the field 

might already have enough statistics on the rate of failures and have enough devices with a 

recognizable pattern of failure modes to implement this study. Assuming that they would be willing 

to share the information or at least input it into a neutral data collection point, laboratory experiments 

could then be conducted with deliberate overstresses aimed at reproducing the pattern of failure 

modes. From similar appearances, inferences might then be drawn on the type of overstress that 

occurred in the field. While recognizing the limitation of such inferences, compared to the ideal of 

actually recording the occurrence of a surge current, this approach would have the advantage of 

representing a summary from the millions of SPDs in permanent service, rather than a few observation 

points by power quality monitors that are limited in number and period of monitoring. Each SPD 

would act as a surge detector, akin to the clock motors that failed and provided surge statistics in the 

early sixties (a 100-to-1 reduction of failures when the withstand capability was raised from 2 kV to 

6 kV), serving as one of the inputs to the data base for the IEEE 587 Guide -- now ANSUIEEE 

C62.41 -- (Martzloff and Hahn, 1970)[3]. 

The cooperation of all organizations and individuals would be coordinated in cooperation with the 

IEEE and other standards-developing bodies. At this point, the thought of collecting failure 

information that some parties might wish to keep proprietary may appear to be wishhl thinking. 

However, it is proposed for consideration and discussion, with the hope that the advantages of 

pooling data would help overcome concerns about any inadvertent disclosure of sensitive information. 

Other field failure chta 

In addition to the clock motor story cited above, other common appliances can be viewed as 

unwittingly serving as surge or swell recorders. A very humble appliance, the incandescent light bulb, 

is a good example of how at least a "reality check" can be applied in assessing the surge environment. 

Anecdotal information collected by the author in the seventies, and now in the process of being 

updated at the Power Electronics Applications Center, shows that most light bulbs fail when 

subjected to surges in the range of 1000 to 1500 V. The failure mechanism of a light bulb under 

surge conditions involves an internal flashover bypassing the hot filament, triggered by the surge and 

followed by a power-fi-equency arc that bums out the filament at its point of attachment to the stems. 

The internal fLse in the bulb base then clears this power arc. From the fact that billions of light bulbs 

are connected to the 120 V systems in the United States, and only sporadic occurrences are reported 

of failures in excess of that implied by the published life of the bulb, it seems that occurrence of surges 

above 1500 V is not very frequent. 

250 POWER QUALITY SOLUTIONS SEPTEMBER 1995 PROCEEDINGS 
There are some limitations to the conclusions that can be drawn from such experience, such as the 

competing mechanism of excessive rms line voltage, unknown variation among bulb designs, etc. 

Nevertheless, the large number of data points resulting from the widespread use of light bulbs makes 

the data a reliable source of information if it is not misconstrued as pinpointing a narrow band of 

failure levels. Other appliances might also be used as unwitting surge recorders if their manufacturers 

and users would consider sharing field-failure information. 

CONCLUSIONS - AN OPEN INVITATION 

The two approaches presented in this paper are rooted in the expectation that enough interested 

parties would be motivated to participate in a pooling of information. Thus, the conclusions of this 

paper take the form of an open invitation to individuals and organizations for serious consideration 

(including peer-review criticism of the ideas) and, hopeklly, participation in the data collection. 

The first approach will require the development of a transducer box containing one or several 

varistors and an appropriate (moderate accuracy for low cost) current transformer. If such a 

transducer box can be developed and accepted for across-the-line connection, the next step would 

be to recruit enough participants willing to acquire the box and use their existing commercial 

monitor(s) to record the occurrences of such currents. 

The second approach will require a policy decision by manufacturers that the perceived disadvantages 

of disclosing failure rates to a third party -- even with assurance of good faith custody of the 

information -- would be more than compensated by the benefit of a better characterization of the 

environment in which their products must operate. 

Individual researchers and organizations are explicitly invited to contact the author with comments, 

suggestions of alternate approaches, and ideas for implementing this change in characterizing the 

surge environment. 

ACKNOWLEDGMENTS 

Alex McEachern and Don Worden contributed comments on the ideas presented here, at an early 

stage when the idea was presented in a two-page flyer distributed among IEEE colleagues, resulting 

in some evolution of the concept. The still anecdotal data on varistor characteristics and light bulb 

failure levels have been collected at the Power Electronics Applications Center in Knoxville, 

Tennessee. It is expected that more comprehensive tests will be pursued, leading to a formal 

publication of the results. Kermit Phipps contributed the information on the characterization of 

varistors for an eventual staircase configuration, and Doni Nastasi contributed the information on the 

failure levels of light bulbs under surge conditions. Thomas Key and JoAnne Surette reviewed the 

draft of this paper and made thoughtful suggestions. All are gratefully acknowledged. 

POWER QUALITY SOLUTIONS SEPTEMBER 1995 PROCEEDINGS 251 
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