should the proposal attract sufficient interest from the EMC community. As it turned out, the response was polite 

interest but no action. 
SURGE RECORDINGS THAT MAKE SENSE: 

Shifting focus from voltage to current measurements 

Franqois D. Martzloff 

National Institute of Standards and Technology 

Gaithersburg MD 20899 USA 

Abstract - The paper proposes to establish a program for 

characterizing surge events according to the capability of a 

surge event to deliver a surge current through the power 

system in end-user facilities. This characterization would 

replace the conventional and by now misleading monitoring 

of surge voltages. The new approach will use a current 

transducer including a silicon-avalanche diode with the 

lowest possible voltage to "attract" surges away from other 

surge-protective devices connected within the facility. The 

voltage signal from the current transducer will then be 

recorded using any power quality monitoring instrument 

available to the individual researchers, providing complete 

current waveform parameters. 

I. INTRODUCTION 

1.1 Background 

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 ERA (Bull and Nethercott, 1964)[1], General Electric 

(Martzloff & Hahn, 1970)[2], IBM (Allen & Segall, 

1974)[3], Bell (Goldstein and Speranza, 1982) (41, Canadian 

Electrical Association (Hughes & Chan, 1995)[5], National 

Power Laboratory (Dorr, 1995)[6] and other researchers, 

including Hassler & Lagadec (1979)[7], Meissen (1 983)[8], 

Wernstrorn et al. (1984)[9], Goedbloed (1987)[10], 

Standler (1989)[11], and Forti & Millanta (1 990)[12 1 have 

been limited to the measurement of transient voltages. 

We now propose a change in the protocol for the monitoring 

of power quality in ac power systems. This change has 

become necessary because end-user power systems are no 

longer what they were at the time the early surveys of 

transient overvoltages were conducted. Varistor-based 

surge-protective devices (SPDs) have become so ubiquitous 

in low-voltage ac power systems that hardly any location can 

be found where there is not some form of transient voltage 

limitation in effect. Attempting now to characterize the 

environment so that appropriate SPDs could then be 

prescribed for specific locations based on voltage 

measurements would be quite misleading. What such a 

measurement would yield today is no longer the surge 

characteristics of themonitored system, as it was at the time 

of the early surveys, but the residual voltages of whatever 

SPDs are installed nearby. 

Electlicity Divirion. Electronics and Electrical Engineering Laboratory, 

Technology Admini.rtration, U.S. Department of Commerce. 

1.2 Making meaningful measurements 

The proposed change in monitoring practices is to insert 2 

current transducer between the low-voltage power system 

being monitored and the existing monitoring instruments 

This transducer would consist of an SPD with the minimum 

tolerable voltage rating across the power line, to be 

connected at some point of an installation, and serve as 2 

"magnet" for attracting the impinging surges. To use 2 

metaphor, this SPD in effect becomes the "winning bidder' 

by offering to the impinging surge the path with lowesl 

clamping voltage among all the parallel-connected SPDs o 

the installation. 

A current transformer with the "magnet SPD" in the primar! 

and an appropriate burden on the secondary would be usec 

to feed the resulting voltage signal into the existing powa 

quality monitoring instruments now used by man) 

organizations and individual researchers. In this manner 

the surge current attracted by the "magnet SPD" can bc 

recorded to find the true character of surge events at thal 

particular location, despite the presence in the local systen 

of any and many unknown and uncontrolled SPDs. 

11. TRANSDUCER DESIGN 

11.1 Breadboard design 

Preliminary results on the feasibility of such a recording 

system have been obtained: a suitable silicon avalanche 

diode has been identified and proven to act as a "magnet,' 

even in the presence of "competing" metal-oxide varistors 

and yet able to withstand the temporary overvoltages tha~ 

can occur in the system. At this point, the transducer desigr 

principle is well defined, and concerns that the "magnet' 

effect could be effective only within a small power systerr 

have been addressed, as discussed later in the paper. 

The current transducer would consist of a string of silicor 

avalanche diodes (SADs) in series with the primary of : 

current transformer with a burden connected across it: 

secondary, an overcurrent protective fuse in series with tht 

diodes, and an indicating light to signal a blown fuse. In the 

final design that would be used to deploy a number of these 

transducers, all of these components will be included in 2 

package derived fTom the so-called "plug-in SPD" whick 

are offered by many manufacturers. Using the externa 

package of such a device will provide a low-cost envelopc 

to build a few hundred transducers with no tooling costs anc 

yet provide a package suitable for connection to wal 

receptacles in end-user systems. 
The power system can include several branch circuits to 

supply the loads, some of which featuring SPDs incorporated into load equipment or installed by the end-user. At 

some point of this system, selected for convenience by the 

instrument operator, the transducer will be installed. A key 

point of the proposal is that pinning down the actual location 

of the monitor is no longer a concern because of the 

"magnet" effect of the low-clamping SAD string. 

Figure 1 shows a schematic diagram of the transducer. 

Selection of an appropriate string of SADs is an exercise in 

brinkmanship: the SAD string must have a clamping voltage 

sdciently low to make it the winning bidder, and yet not so 

low that the temporary overvoltages occurring in the power 

system would destroy it. In a preliminary experiment, a 

SAD string with a nominal voltage of 185 V at 1 mA dc was 

found to survive exposure to 130% of nominal 120 V 

system voltage, ensuring sufficient distance from the brink 

of failure. 

It will be prudent to include a fuse in series with the SAD 

string for the case where a large surge would exceed the 

current-handling capacity of the SAD string and cause its 

failure. A visible indication of a blown fuse can be added to 

the package, similar to theindication now routinely provided 

by the commercial plug-in SPDs offered for residential use. 

A commercially available and low-cost current transformer* 

has been identified that can provide sufficient accuracy for 

the measurements over a sufficient frequency range. 

Conventional current-viewing transformers used in the 

laboratory are much more expensive and would not be 

necessary for the purposes of the recordings. Considering 

the wide range of surge events and the resulting statistical 

uncertainty in citing "representative values" of the surge 

events, obtaining results of current measurements within an 

order of magnitude is already a very large improvement over 

thepresent lack of knowledge. In the example of recording 

capability discussed later in the paper, there is a 50:l 

difference in the cost of a laboratory-type current-viewing 

transformer and the low-cost current transformer required 

for deployment of a large number of monitors. 

Matching the burden values to the voltage requirements of 

the monitor input circuits has not yet been done at the time 

of this writing, but might be reportable by the time of 

presentation of the paper. Tradeoff between the cost of the 

current transformer and its frequency response is another 

area where improvements to the proposal can be made to 

obtain meaningful recordings at a cost that will not be a 

deterrent to acceptance of the proposal. 

* Please note that rhe author has no vesred interest in promoring 

or endorsing any hardware, and that thefinal selection of the 

cuwent transformer is still an open design tradeoficonsideration. 

Commercial availabiliry is cited here only in support of the 

concept of using readily available, low-cost components for the 

deployment of many transducers. 

I 185 V SAD sUng 

Figure 1 - Schematic of the transducer 

11.2 Radius of attraction 

By design, the string of diodes is intended to become the 

"magnet" that will attract the impinging surges. We 

recognize that this winning bid can be ensured only within 

a certain radius from the transducer. Increasing distances 

between the transducer and competing SPDs eventually 

produces a decoupling of the two devices and might allow 

a competing SPD connected upstream from the transducer 

to divert the surge first. This situation is the reverse of that 

sought when making studies of the coordination of cascaded 

SPDs, where the concern is to ensure that a heavy-duty SPD 

located upstream of a lower-duty SPD is sufficiently 

decoupled so that an impinging surge will be diverted by the 

upstream SPD. The parameters of cascade coordination 

have been addressed at length in the literature [13], [14], 

[I 5 ] and will not be discussed here, but serve as a useful 

reminder to take a careful look at possible limitation in the 

radius of meaningful measurements. 

To ascertain that the transducer will remain the winning 

bidder, a simple test was performed by assembling a 

physical mock-up of an installation with a service panel 

feeding three branch circuits, with lengths of 4.5 m, 9 m, 

and 18 m respectively. The SAD string was connected at 

the end of one branch circuit while metal-oxide varistors 

(MOVs) with nominal 200 V at 1 nlA dc were connected at 

each end of the other branch circuits. 

* 

SAD 

Figure 2 - Arrangement of competing SPDs 
We can expect that the least favorable combination would 

be that of the SAD connected at the end of the longest 

branch circuit, with an SPD of relatively low clamping 

voltage installed at the end of the shortest branch circuit. A 

Combination Wave (161 was applied to the service panel, 

and the currents in the three branch circuits were monitored, 

with the SAD string successively connected at the end of the 

4.5 m, 9 m, and 18 m branch circuits. In all three cases, the 

SAD attracted all the surgecurrent, with no current detected 

in the MOV-terminated branch circuits. 

More sophisticated analysis can be performed by applying 

the numerical modeling techniques developed in the referenced modeling studies [17], 1181, extending the distances 

and combinations of competing SPDs from the simple 

example shown in Figure 2 to determine how extensive an 

installation can be and still have the transducer remain the 

winning bidder. In this manner, the pitfall that threatens 

credibility of contemporary voltage recordings (uncertainty 

about other unknown SPDs connected in the system that can 

produce misleading results of low surge activity) will be 

eliminated. 

111. BREADBOARD TEST 

A simple breadboard was assembled with the 185 V SAD 

string connected to the output of an 8/20 ps surge generator 

and a 100 S1 resistance inserted in series to limit the current 

delivered by the low-impedance generator. The resulting 

current (longer than 8/20 ps because of the inserted 

resistance) was applied to the one-turn primaries of a 

laboratory-grade current-viewing transformer and of the 

low-cost current transformer, with a 2 l&2 burden across its 

secondary. Their secondary output voltage was recorded by 

a laboratory-grade digital signal analyzer. Figure 3 shows 

the recorded voltage across the SAD string and the two 

current signals. 

1...;;;;;;::: . . .. ................................ " ,,,,.. ,", 

0 10 20 30 40 50 - - .. microseconds 

Figure 3 - Voltage across the SAD string and 

corresponding current signals delivered by the 

laboratory-grade transformer and the breadboard 

current transducer 

To make the comparison easier, the signal analyzer input 

sensitivity of the two current-displaying channels was 

adjusted so that the two current signals would coincide near 

their peaks. The point to be made here is not the actual 

numerical values, but the quality of the frequency response 

of the low-cost transducer, illustrated by a time-domain 

representalion of an impulse. 

Inspection of the two current traces shows a loss of signal 

at the front as well as in the tail, symptomatic of a limited 

frequency response. While such a loss would be absolutely 

intolerable in a laboratory environment, we must place it in 

its proper perspective. As outlined in the introduction, we 

are now facing a new situation, brought about by the 

proliferation of SPDs, where surge voltage measurements 

no longer have the significance they once had, so that we 

have no knowledge on the real surge threat existing in the 

system. The current-delivery capability of the surge event, 

as recorded by the imperfect current transducer is an 

immense improvement over the present total lack of 

knowledge. 

Given the wide range of possible surge events, the relatively 

small loss of information represented by the two areas 

separating the two current signal traces is small compared 

to the common area that represents a good estimate of the 

order of magnitude of the current-delivery capability of the 

recorded surge event. In contrast to laboratory measurement 

researchers, operators and users of field surveys are already 

content to have the surge events characterized within one 

order of magnitude when the alternative is no meaningful 

information at all. As discussed earlier, tradeoff between 

transducer cost and quality of the frequency response is still 

an open consideration, for which comments from interested 

parties are earnestly invited before implementation of the 

proposal is initiated. 

IV. PROGRAM IMPLEMENTATION 

The next step in making the change from surge voltage 

recording to surge current recording would be to recruit 

enough participants willing to acquire the transducer and 

use their existing commercial monitor(s) to record the 

occurrences of surge currents attracted by the transducer. 

This transducer could beproduced in cooperation with some 

manufacturer of a plug-in SPD, so that a readily adaptable 

outside package could contain the transducer components 

and provide a simple and safe way of connecting it to a 

receptacle. 

Within the EEE, a new Task Force of the Standards 

Coordinating Committee on Power Quality is developing 

protocols for reporting monitoring results; hopefully, the 

concepts presented in this paper will be taken into 

consideration by that Task Force and by other organizations 

interested in making surveys for characterizing the 

electromagnetic environment. The IEC is also considering 

the development of guidance documents on measurement 

methods in the area of power quality, where this shift of 

focus should be taken into consideration.