Systems and 

inhments in site 

surveys 

Franpis D. Markloff 

National Institute of Standards and Technology Gaithersbura Marviand 

Thomasm. GRLS 

Liebert Corporation Columbus, Ohio 

Every on-site survey of power quality utilizes a 

variety of methods and instruments, requiring careful interpretation of survey results. A close 

examination of underlying assumptions in nine 

published surveys shows that some diierences 

can be reconciled, but indides the need for 

new or improved standards. 

P ower quality surveys have 

been conducted for two reasons: l) to identify potential 

problems or causes of equip 

ment disturbances at a specific site. and 2) to develop a broad 

data base with the hope that the general findings will be a plicable in specific cases. This art& gives a review 

of nine papers reporting broad data 

base surveys. but the conclusions are 

also applicable for site-specific surveys. The review shows problems that 

readers encounter when different 

authors use different instruments, different definitions, and as a result 

sometimes reach contradictory conclusions. The nine surveys were conducted in the United States and 

Eumw over the last 25 "ears. Power 

s tern have not changed much, but 

xe load equipment charactrr~st~u, as 

well as the capabilities of d~sturbance 

monitoring instruments, have 

changed considerably. Table 1 shows 

details of the locale, system voltage, 

instrument type, and connection 

mode as described in the papers. 

Bull and Nethercot. in a 1964 article 

111, report monitoring performed in 

the mid 1960s on 240-V systems in 

Great Britain with instruments of 

their design. Their initial insmunent 

used vacuum tubes, leading to the 

developnlent of a solid-state circuit 

which may be considered the forerunrer of modern monitors. The insmment had several channels, each with 

a different threshold. 

The monitoring locations were 

selected to include a variety of conditions, with data being collected for 

several weeks at each location over a 

total period of 2 years. The results do^. 

not mention transients above 600 V; 

it seems that no channels were 

provided above that level because the 

authors were only concerned with the 

range of 50-600 V. 

Martdoff and Hahn, in a 1970 paper 

121, ~porr the highlights of measurements made in the 1963 to 1967 

period on residential, commercial, 

and industrial circuits, mostly singlephase 120 V. Waveform data were 

obtained with commercial, custommodified oscilloscopes fitted with 

motor-driven cameras. These milloscopes were installed at various locations where transient activity was 

suspected, not at randomly determined locations. In addition, a peak 

counter circuit was developed, and 9l 

units with a 1200- or a 2000-V 

threshold were deployed at 300 locations where there was no prior suspicion of unusual transient activity. 

The oscilloscope data gave one of 

the first indications that the traditional unidirectional impulse, long 

used for dielectric testing, might not 

be representative of surges occurring 

in low-voltage circuits. The threshold data indicated locations where 

surges above 1200 V occur frequently 

(about 3 percent of the sample). 

while other locations appear far less 

exposed to surges. The 100:l reduction of an alarming failure rate of 

clock motors, achieved by increasing 

the surge wirhstand capability of the 

motors from 2000 to 6000 V, is documented in that paper. 

Cannova, in a 1972 paper 131. 

reports the monitoring of surges on 

U.S. Navy shipboard 120- and 450-V 

power systems in the late 1960s. 

Instrumentation used for the initial 

phax of the monttonng program consbtcd d 0Klllowopt.r blmdar to those 

rwed bv Mamloff. Pnwuon was also 

inchdid for the option of measuring 

the transients alone (through filters) 

or superimposed on the ac line voltage; this option reflects the old dichotomy. still unsettled to this day, as to 

whether the transients should be 

measured as an absolute value or as a 

deviation from the instantaneous 

value of thc ac sine wave (see the last 
Power Quality Surveys 

column of Table 1). 

The results are not rewrted seoaratelv for 120- and 450-V 

systems; therefore. it is iot possilde to express them in terms 

of per-unit or percentage of nominal system voltage. Cannova's statistical treatment aims at fining the recorded nansients to a normal distribution and concludes that a log 

normal distribution is a better fit. A brief statement is made 

on the durations of the recorded transients (without a statement on how thme durations are defined), citing a majority 

of durations between 4 p and 6 p, with a few at 19 p. 

Fmm the data base. acknowledged to be a small total number of events, a protection level of 2500 V'was defined. The 

specification of a 2500-V 1.2150-ps voltage withstand by 

DOD STD 1399 was derived from this survey. 

Two aspects of the conclusions are espially worth noting: 

1) there was no information on the source impedance of the 

surges, and yet the data eventually served to specih requirements for surge protective devices; and 2) a large difference 

in frequency of occurrence was noted among ships of the 

same type and class, similar to the okrvations on land surveys. 

Ah and Segall, in a 1974 paper 

141 report the monitoring of several 

types of power disturbances at computer sites, performed with oscilloscopes, oscdlographs, and digital 

instruments, in the 1969-1972 

period. Details of the instrumentation were described in a separate 

paper 151. Disturbances are 

described as overvoltages and undervoltages, oscillatory decaying disturbances, voltage spike disturbances, 

and outages. The tern sag and 

"surge" ("swell") had not yet made 

their appearance in the jargon. 

The survey was conducted in two 

phases. In a fmt phase, reliminary 

information was obtainJon ranges 

of disturbances. leading to the 

development of a second generation 

of monitors deployed in the next 

phase. The recorded disturbances 

are described by plots and histograms. The highest surge recorded 

in the first phase is shown as 350 V. 

In the second phase. the monitors 

grouped all surges into three categories, the hiighest having a range of 

100 percent (of line voltage) to 

infinity. so that no detailed information is provided to describe high 

peak values. The survey does report 

in detail the occurrence of undervoltages and overvoltages, providing 

a basis for the comparisons with the 

Goldstein-Sperama results. 

Goldstein and Speranm, in a 1982 

paper 161, report the monitoring of 

several types of disturbances at a 

variety of locations in the Bell system, with digital multiparameter 

tmrrumeno. in the 1977 and 1979 nd The conditions of 

the survey are documented, ~ncl ur ing mtrument ' locations 

and dcfmmons of the parameters as well as the methods of 

data processing. 

The findings are briefly reported with emphasis on predictions for disturbances expected at specific sites. The prediction is obtained by using a statistical model derived for all 

sites and making adjustments reflecting specific site wndirions determined by a limited survey at that site. The 

authors are emphatic on the point that the lack of correlation 

between sites prevents blanket a~~licationf the overall findings to any skific site, but thai-useful predictions are possible by combining the overall data with limited knowledge on 

specific site data. 

Weinsrrom, Brans, and in a 1984 report published 

in Sweden and circulated in the United States as an English 

draft translation 171, report monitoring of industrial 2201380- 

V svstems bv dieital multithreshold instruments. comborated , - 

by Laveform recording with digital storage oscilloswpes. 

The padmeten to be rccurJed and reported are defind in an introductory section; however, their description of "common 

mode" and "differential mode" in the English translation does 

not correspond exactly to symmetrical and asymmetrical voltages defined by the IEC. 

The range of surges recorded extends from 200 ro 2OOO V. 

la) Mimorecondr Microrecondr 

Figure 1. 

"Typical" wavefimns repmted in sire surveys include three examples of surges recurded 

by Mmtzloff (a); rypicd wuvefinm uccordiq to Goedblued (b); desm'ption of wuuefurm 

Cunnovu (c): desmiption of wuaefum by Odenbery-B~arkuh (d); and three examplrs 

of .surges recmded by Wrmstrom, Broms and Boberg (e) 
Power Quality Surveys 

In a summary tabulation, rise times are shorn as ranging 

from 20 to 200 ns and duration from 0.2 to 2.5 p. The 

results show a wide difference of surge activity among sites 

hut a relatively constant slope of the rate of occurrence versus level. 

Aspnes, Em, and Mmitt, in a 1985 paper 181, report a 

survey of the power quality in rural Alaska at isolated power 

eneration facilities. The monitoring instruments are identi- 

!ied as one of the contemporary commercial digitizing monitors. A very comprehensive summary of the recordings is 

presented including frequency deviations (a unique situation 

in these isolated systems), sags and "surges" ("swells"), 

impulses (i.e., surges,), and outages. Some ambiguity arose 

because of the possibility that built-in surge rotection in the 

mcnitors might have attenuated the surges king recorded. 

Odenberg and Braskich, in a 1985 paper 191, report the 

monitoring of computer and industrial environments with a 

digital instrument capable of the simultaneous recording of 

voltage surges and current surges. This new capability for 

relating voltage and current shows a growing awareness of the 

need to monitor current surges - an improvement over previous surveys limited to the measurement of voltages. 

However, the remrted suree currents are those of a current 

toward undef~nhd loads dgwnstream ~~~~~ from ~~- ~~ the ~~~- instntrnenr: ~ .... 

they do nut ~nclude al.y nlmsuremcnt of the cuncnt rhrough 

p shunr-connrircd surge dwerter, a measurement that would 

have provided new information on the source impedance of 

the surges. 

The digital processing applied by the instrument yields two 

points of the surge: the peak value with the time to reach 

peak and the time elapsed until decay to 50 percent of the 

peak value. From these two points, a "waveform" description 

is proposed without any other information on the actual 

waveform. From a large number of recorded surges (mote 

250,000 events) a startling finding is cited: 90 percent of the 

recorded surges have their 50-percent point in a narrow window of 900-1100 p. Attempts to reconcile this singular 

finding with the observations reported by other surveys have 

not been successful. 

Goedbloed, in a 1987 paper 1101, describes in detail a custom-built automated measurement system monitoring 

2201380-V networks in Europe. The automated measurement 

system reflects the progress made in digitizing techniques 

since the days of vacuum tubes. By combining two commer- cial recorders with a custom interface, the developers 

obtained detailed recordings with a 10-ns sampling interval 

and 20-p window on the first recorder and a I-p sampling 

interval and 2-ms window for the second recorder. 

The system included a provision for automated data reduction, yielding raw data as well as statistical information on 

amplitude, rate of rise, energy measure, spectral density, and 

conversions from time domain to frequency domain. With a relatively low threshold of 100 V above the line voltage, the 

distribution of occurrences is weighted toward low amplitudes; nevertheless. occurrences are reported above 3000 V. 

Relalive Occurrence of Different Types ot 

Disturbances 

Two of the surveys reviewed in this paper have been 

widely cited, one performed in the early 1970s by Allen and 

Segall (A-S for short) 141, and the other performed in the late 

1970s by Goldstein and Speranza (G-S) (61. However, the 

findings do not at first appear to be in agreement; a detailed 

comparison of these two surveys provides a god illustration 

of the pitfalls of superficial interpretation of Survey results. 

A cursory comparison of the results might lead one to 

conclude that a significant change in power disturbances at 

computer sites occurred between 1972 (end of the A-S study) 

and 1979 (end of the G-S study). A-S re rted 88.3 percent 

of observed disturbances as spikes, impugs, and transients, 

11.2 percent as sags, and 0.47 percent as outages. G-S, on the other hand, reported 87 percent of the observed disturbances as sags, 7.4 percent as impulses, 0.7 percent as "surges" ("swells"), and 4.7 percent as outages (which they 

call power failures). 

Taking a more careful look at the monitoring thresholds 

used in each study helps to explain why the number of 

impulses a pear to have decreased and the number of sags 

appear to Rave increased. since G-s use a threshold of -4 

percent for sags while AS use - 10 percent. one can expect 

the G-S study to indicate a higher percentage of sags, lxcause 

the sags between -4 and -10 percent are not included in 

the A-S study. Oxilktory decaying disturbances are not 

ifically identified in the G-S study but are included under 

gcategoq of impulses. The threshold for impulses used by 

G-S (200 V for 120-V lines, or 118 percent) is higher than 

that used by A-S (&I0 percent). Because the rate of occur- rence increases steeply for lower amplitude disturbances, one can expect a drastic reduction in the percentage of impulses 

reported by the G-S study as compared to the A-S study. 

The increase in percentage of wer outages reported by 

G-S may be ex lained by the shirin the number of disturbances observecfdue to other threshold changes. Percentages can be a very misleading basis for comparison unless all conditions are eaual. For examole. the incidence of Dower outages obxrved'm borh studlei rs very sm~lar, even ihough the 

percentages are one order of magn~tude apan. A.S report 0.6 crcunence per month shtle GS report 0.4 occurrence per 

month. 

When the distlhance rates at the same thresholds are 

compared for the AS data and the G-S model (for 75 percent probability), the results are surprisingly similar. The 

conclusions of these two studies are that deep sags contribute 

about 62 percent of the power system problems which are 

related to normal mode disturbances, severe impulses are responsible for 21 percent, outages for 14 percent and "surges" 

("swells") for 2 percent. 

Difierrnces in Surge Amplinrdes 

The am litudes of the surges reporred in the surveys vary over a wiJ range, and comparisons are difficult because the 

data are not presented in a uniform format. An attem t was made to get a quantitative comparison of the ampitudes 

reported in the surveys; however, the exercise was quickly 

found to be futile because of the following two main reasons. 

1) looking at "maximum values," one finds that in some surveys the quoted maximum is actual1 a value in excess of the range of the instrumentation. wiile for others it is 

the measured value. There are too few points and information is insufficient to artem t a statistical treatment of 

this truncated data base. ~urtEermore, the quoted value 

in some surveys is the total volrage (instantaneous value of ac sine wave plus surge), while in others the sine voltage 

has been filtered out. When surges are in the range of 

several thousand volts (the concern being damage), the 

difference between the two defmitions is not significant; 

however, when surges are in the range of a few hundred 

volts (the concern beii malfunction), the difference is 

significant. 
Power Quality Surveys 

2) Because the lower threshold of the recorders varies among 

surveys, and the frequency of occurrences increases dramatically with lower thresholds, the labels of average. 

median, most frequent, typical, etc., are not meaningful for com aring amplitudes. The preceding discussion of 

A-S an2~-s results has illustrated the profound effect of 

threshold selection on reported results when they are 

expressed in percentages. 

A general explanation of differences in amplitudes found 

in the various surveys might be the observation by some of 

their authors of the lack of correlation between sites. Fwthermore, some surveys include sites where equipment 

failures were experienced or expected, while other surveys 

were made at sites not singled out for particular problems. 

Thus the differences in overall results of various surveys 

might simply be the result of the different surge exposure at 

the points of monitoring. This explanation implies that surveys will still be needed where specific information is desired. 

Differms in Wawfm 

From those surve s made with waveform recording 

the "typica?' forms suggested by each author have 

~~~:C(&ted in Fire 1. The findi of ringing waves, as 

opposed to the traditional unidirectionz impulses, seems general in these low-voltage circuits.4 

Mamloff and Hahn were among the first to report ring 

waves. Their reported measurements were incorporated into 

the data that resulted in the eventual selection of a 100-kHz 

Rii Wave with a 250- or 500-ns rise time for the UL Standard Ground Fd Circuit Intemrpterr 1111 and the 0.5-p 100- 

Irtll Ring Wave of the lEEE Guide on Surge Voltages 1121. 

While Cannova does not report detailed descriptions of 

the waveform, the statements "4 to 6 p" and "up to 19 p" could be interpreted either as a time to half-value or as the 

time between the initial rise and the first zero crossing of a 

ringing wave. Interestingly, chat data base led to the qxcification of a unidirectional longer impulse, the classic 

1.2150-p voltage impulse, for conservative rating of candidate surge protection devices to be installed in the shipboard 

environment [13]. 

Wemsmnn, Broms, and Boberg show three examples of 

recordings. The first is indeed a ring wave with a frequency 

of about 500 kHz and a rise time of 200 ns. The second 

example is a burst of nanosecondduration transients, similar 

in shape to the proposed IECITC~S Electrical Fast Transients 

1141. The third example is (of all things) a unidirectional 

(almost) impulse. The data reported by Odenberg and Braskich are different 

from the others in that only ovo poinrs of the waveform are 

reported: peak and 50 percent of peak amplitude. As such, 

this description is not a complete waveform; furthermore. 

their report that 90 percent of their 250,000 recordings show 

the SO-percent point occurring between 900 and 1100 p is 

Survey Period Locale 

Circa Great 

1962.1963 Britain 

M-H 1963.1967 USA 

Circa 

1969.1972 

1977-1979 

Circa Sweden 

1982-1983 

(Alaska) 

1982-1983 

Gw circa Europe 

1983.1984 

.Principal type stated first. 

"See description in text. 

I - -- -- -. 

Dem'k of nine Whed on-site power quai~ty su~veys, including lo&, type of system, volrage, instrument cype and 

connection mode I 
Power Quallty Surveys 

uni ue arno all the surveys. 

Ae ~ozbloed data presentation reflects concerns 

addressing interference rather than damage; hence, the 

em hasis was given to amplitude, rate of rise, and energy 

rat R er than waveform. An odcilloeram characterized as ''mi. 

cal" is resented in Figure 1, a ri$ wave with a heqi&$df 

about h kHz. 

Thus, the ambiguities plaguing the field of site surveys 

have become apparent to many interested workers, resulting 

in the formation of a new Worki Group Monitoring Electrical quality spomred by a new iEEE Standard Winating Committee on Powet Quality. Stay tuned in thb area; 

contributions to rhe development of a new standard by this 

working wup are invid and welcome, and further information may be obtained from the authors, 

Oonchrdon 

A review of power ualiry site surveys umducted over the 

last twenty years revea e interesting facts, and close examina. 

tion of the results can dispel some fictions and Mlacies. 

1) Considerable progress has been made in the recording 

capabilities of monitoring instruments, mostly as the result 

of progress in the hardware and software used in digitizing 

systems. Among the many im rovemena an multichannel synchronized recording o ! different parameters, fast data acquisition, automated data reduction, and improved 

resolution. 

2) With the steady progress and expanded capability of 

instruments, it becomes increasingly irn ant to achieve 

greater consistency in definitions o P" the disturbance 

parameters and the methods of application of the monitoring imtruments. 

3) Site-to-site variations in e res reclude malci 

cise predictions for a specxite !om an over# &: 

k, but useful predictions can be made by adjusting the 

overall data base only slightly by limited data collection at 

the site of interest. 

4) The steady increase in the number of surge protective 

devices being installtd in lowvoltage power circuits in the 

last several years can be expected to continue. The result 

rmght be a lowering of the mean values of observed surges 

but not necessarily the extreme values of the distribution. 

5) Differences among results indicated by a cursory comparison can in many cases be resolved by a closer examination of the conditions under which the surveys were 

conductad However, some differences appear less likely 

to be explained if raw data have been processed and the 

initial patmeter measurements are no longer available for 

consideration. Providing greater detail in the published 

repom and sharing of experiences at technical meetings might help overcome this difficulty. 

6) A new IEEE Working Group on Monitor' Electrical 

Quality has been formed with a broad aoope%at mmm 

pag~es this ptgcm of improving consisrency in the defini. 

Power Quality Surveys 

tions and interpretation of power disturbances. In addition, 

the IEEE Working Group on Surge Characterization is also 

attempting to obtain a hader data base for the revision of 

the Gtlide on Surge Vdtuges. These two ups are ready to 

provide counsel and forum to any would- r surveyor in planning and reportin the collection of new data on distutbances, thus avo' d ing later difficulties in incorporating the 

results in a shared data pool. 0 

Refemme8 

[I] J.H. Bull and M.A. Nethercot, "The Frequency of 

Occurrence and Magnitude of Short Duration Tram 

sients in Low-Voltage Supply Mains, " Radio Elecmic 

Engtneer, Sept. 1964. 

[2] F.D. Martzloff and G.J. Hahn, "Surge Voltages in Residential and Industrial Power Circuits," IEEE Trans. 

Power App. Syst., vol. PAS-89, no. 6, JulylAug. 1970. 

131 S.F. Cannova, "Short-Time Voltage Transients in Ship- board Electrical Systems," in IEEE IAS I972 Annual 

Meeti Cod. Rec. 

141 G.W. 3 en and D. Segall, "Monitoring of Computer 

Installation for Power Line Disturbances," presented at 

the IEEE PES Winter Meeting conference, New York, 

Jan. 1974, Pa r C74199-6. 

151 G.W. Allen, &ign of Power-Line Monitoring Equi 

rnent," IEEE Trans. Powet App. Syst., vol. PAS- , no. 6, Novhc. 1971. 

8 

[6] M. Goldstein, and P.D. Speranza, 'The Quaiity of 0.S. 

Commercial AC Power," in Pm. INTELEC Conf., 

1982. 

[7] H. Wemstrom, M. Broms and S. Boberg, "Transient 

Overvoltages on AC Power Supply Systems in Swedish 

Industry," Foorsvarets Forskningsanstalt, Huvudavdelning 3, Sweden, Report FOA E 30002-F2, 1984. 

[$I J.D. Aspnes, B.W. Evans and R.P. Merritt, "Rural 

Alaska Electric Power Quality," IEEE Trans. Power 

Ap Syst., vol. PAS-104, no. 3, Mar. 1985. 

[9] R. OL! enberg and 8. Braskich, "Measurements of Voltage 

and Current Surges on the AC Power Line in Comuter and industrial Environments," IEEE Trans. ! ower A p. Syst., vol. PAS-104, no. 10, Oct. 1985. 

1101 J. J. ~oedbf oed, "Transients in low-Voltage Supply Networks," IEEE Trans. Electromagn. Cornpat., vol. 

EMC-29, no. 2, May 1987, 

[ll] UL Stutuld for Sufety 943, Ground Fault Circuit Intempms, Underwriters Laboratories, 1976. 

[12] Guide on Surge VoItages in h-Vdtage AC Pawr Circuits, ANSVIEEE C62.41-1980. 

[13] lnmface S&d fm Shipbarrd Systems, DOD-STD-1399, 

Sec, 300, 1978. 

[14] Electrical Fast T~mient. - Burst Requisements, IEC Standard 801-4. 

Please rate Ihls artlcle on the reader sewice card,. 

Useful, 207; Somewhat Useful, 208; Not Uml, 209