Power Quality Measurements:

Bringing Order out of Chaos

François D. Martzloff

National Bureau of Standards

Reprinted from Proceedings of the Energy Technology Conference, February 1988, Government Institute Pub

Significance

Part 6: Textbooks, tutorials, and reviews

The quality of the power supplied to sensitive electronic equipment is an issue that has been debated

since the 1970s. This paper presents the perspective as of the mid-eighties, reporting on the progress

toward developing power quality-related standards, giving emphasis to the technical aspects of the

measurements, specifically field measurements of power quality.

After reviewing site surveys and their deficiencies or ambiguities, a plea is presented for improving the

usefulness of such surveys by developing uniform procedures and instrumentation algorithms. This ne

was eventually fulfilled by the development of IEEE Std 1159 on Power Quality Measurements, and

reaching the IEC with a standard on the same subject, IEC 61000-4-30:2003, “Testing and Measureme

techniques - Power quality measurement methods.”
ENERGY 

TECHNOLOGY 

"Repowering America" 

Proceedings of the 

Energy Technology Conference 

February 17-19, 1988 

Washington, DOCo 

overnment 

Institutes, Inc. 
POWER QUALITY MEASUREMENTS: 

BRINGING ORDER OUT OF CHAOS 

Franfois D. Mardoff 

National Bureau of Standards 

Gaithersburg. MD. 20899 

ABSTRACT - The quality of the power supplied to sensitive electronic 

equipment is an important issue. Quantifytng this quality, however, is 

difficult under the present state of nonexistent or uncoordinated 

standards concerning two related questions: (I) what levels of power 

quality arc required for what types of loads, and (2) what 

measurement techniques are required to determine reliably the level of 

disturbances that reduce quality. Development of standards by the 

consensus rocess and voluntary compliance. although a slow process, 

is a mec e anism for reaching technically sound and cost-effective 

solutions. Several standards projects are in progress, but need an 

industry-wide support to become the generally accepted basis for valid 

and useful measurements of power quality. 

INTRODUCTION 

The issue of Power Quality has gained increased recognition as 

the result of two unrelated but parallel developments: (1) an increase 

in the sophistication of electronic systems, sometimes resulting in an 

unintentional increase in heir sensitwiry to power suppty disturbances. 

and (2) an increase in the number and power ratlng of 

conversmn equipment, generally resulting in the distortion or: 

power system voltage. lmprovernents in the situation described as 

"poor power quality" can be achieved by reducing the sensitivity of 

equipment to power line disturbances, or by limiting the injection of 

disturbances -- or better yet. by reducing both in a coordinated 

approach. While these remedies might seem obvious in ~rinciple. their 

implementation (enforcement) appears more difficuit. olunra standards provide a guide for .such an implementation. To that en2 three 

types of standards are necessary. The first concerns measurements. to 

obtain correct and universally acceptable data. The second concerns 

equipment performance, to define both its tolerance to disturbances 

and its limits on emission of disturbances. The third concerns acceptable disturbance levels on the utility su~p!y. to promole compatibility 

of equipment with the utility supply. ese standards are develo 

by reconciling "rely technical objectives with economic reality. Ey 

a slsndard to & effective and acccptnble, both aspects rnusl have an 

accurate basis. 

This P aper gives emphasis to the technical aspects of 

the measurements, speci ically field measurements of power quality. 

U.S. Covcrnrncnt work not protected by U.S. copyright. 
ENERGY TECHNOLOGY CONFERENCE 

TI 113 COAL : MATCI IING I!UUIPMENT 

CAYAUII~ W~I mwm UUAU'IY 

To achieve a satisfactory operational environment regarding 

power quality, a coordinated approach is needed to match the 

character~sticr of equipment wi~h those of the power sup~ly. The 

ccrncept of matchin8 is important: it implies actions on bot sides of 

the issues, not un~lateral demands for corrective action based on a 

jsture that the other party is the dfender. Three approaches will 

ead to this matching, separately or in combination: 

I. Increasing e uipment tolerance for disturbances, 

2. Controlling X t e emission of disturbances hy equipment, 

(utility equipment as well as end-user equipment) 

3. Providing interface devices when necessary. 

Each of these three approaches requires accurate information on 

wer supply dislurbances fur any action to be effectwe. Action can 

preventive. when a polenth1 problem is identified before new 

e uipment is instaHed. Action can be curative, when a problem arises 

a ? ter new e uipment is installed. The problem can appear in two 

forms: (11 Qe new equipment is sensitive to disturbances already 

present in the system (the equipment is the victim); (2) the new 

equipment creates a disturbance that affects equipment already in 

servlce (the new equipment is the offender). 

These two terms used to label the situation reveal the adversarial 

postures that can exist. In an ideal world, one would consider total 

s stem goals to optimize economical and technical solutions. rather 

tran Ptnt fingers. In the real world, cooperation can lead to a 

mutua ly satisfactory solution between the soume and the receiver of 

disturbances (note the neutral words) in contrast with the other labels. 

The first step towards reco nizing the need for improving the 

power quality situation is to 8 etermme the level of disturbances 

occurring in the system. The parameters characterizin a power 

supply are: frequency, voltage amplitude. waveform, anj symmetry. 

Therefore, the nature of disturbances may be classified by their effect 

on these four arameten. The severity of disturbances is associated 

with their amp P itude, their duration, and the probability of occurring 

at a given site over P time period. 

The level of disturbances is determined by measurements 

conducted at the site of an existing installation or at a future 

installation of potentially sensitive equipment. These measurements 

are described as 'site surveys.' if the tolerance of the equi ment for 

disturbances is defined a need that is not always recogniredr and the 

level of disturbances determined by the site survey is excessive. then 

the three matching actions mentioned above come Into rla~. An one 

of the three, or a combination. can be the most ef ectlve so r ution. 

Knowledge of the situation will point toward a solution. rather than 

reliance on a common misconception that providing a simple interface 

(line conditioning) will solve all problems. This misconception is 

nurtured by frequent observations that many problems have in fact 

been solved hy sim ly inserting a line conditioner. However, one 

should not yield to I t! e temptation of making a general rule from these 

isolated success stories, and ignore other. more effective or more 

economical approaches achieving inherent compatibili~y. 
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Because this additional line conditioning equipment may require 

significant capital invesrment, the choice of corrective measures is 

made by economic trade-off. However. if technical inputs to this 

trade-off are incorrect because erroneous conclusions result from a 

faulty site survey, the whole rocess is worthless or misleading. For 

this reason, a good understan 'I' ins of the merits and limitations of site 

surve s is essential for reconc~ling expectations with reality before 

speci&ing expensive line conditioning e ui ment. In their review of 

power quahty site surveys, Martzloif an 2 g ruzs ill discussed how one 

should deal, not with fiction or fallacies, but with facts. 

In an attempt to clarify the issues. this paper first presents a 

review of the origins ancl definitions of disturbances. Next, the 

development of monitoring instruments during the last 25 years is 

described. Finally, an appeal is made for im roving measurement 

recorded in future surveys. 

methods to provide more consistent reporting o P power disturbances 

CLASSIFICATION AND ORIGIN OF 

POWER LINE DISTURBANCES 

The four wer system parameters identified above -- frc uency, 

amplitude, wave P" orm, and symmetry -- can serve as frame of re ? erence 

to classify the disturbances according to their impact on thcsc four 

parameters. 

Frequency disturbances are associated with power s stem faults. 

Interconnection of he utility grid ensures frequency sta g iliry, except 

when a fault occurs that asolates the local s stern from the grid. 

leaving local generation more sensitive to loaJ variations. Transient 

frequency disturbances. just before an outage. occur in a system 

containing large rotating machines: should the system trip out. the 

machines will maintain some voltage, with decaying amplitude and 

frequency, while they coast to a final stop. 

Amplitude variations can occur in several forms; their description 

is inextricably associated with their duration. They range from 

extremely brief durations to steady-state conditions. making the 

description and definition difficult, even controversial at times. Their 

causes and effects need close examination to understand the 

mechanisms and to define an appropriate solution. 

Waveform variations occur when nonlinear loads draw a current 

which is not sinusoiclal. One could also describe an amplitude 

variation as momentary waveform variation, but the intended meaning 

of the term is a stead variation of the waveform, or lasting at least 

over several cycles. his type of disturbance is also described as 

harmonic distortion because it is easy to analyze as the superposition 

of harmonics to the fundamental frequency of the power system. 

Dissymmetry, also called unbalance, occurs when unequal singlephase loads are connected to a three-phase system and cause a loss of 

symmetry. This type of disturbance primarily concerns rotating 

machines. and as such is not receiving broad attention. It is 

important however, for machine designers and users. 

the usual description of this type of disturbance, 

by which one phase voltage differs from rhc average The of al percentage three is 
ENERGY TECHNOLOGY CONFERENCE 

The origin of disturbances can he described as external to the 

articular power system. or as internal. In a Iypical situation. the 

poundmy of a power system is defined as the watthour meter. and 

reference is made to the utility side of the meter (external source), or 

to the user side of the meter (internal source). A different approach is to describe the origin in technical terms, such as lightning, load 

switching, power system fault. and nonlinear loads- Dependrng on 

local conditions. one can be more important than the others, but all 

need to be reco nized. The mechanism involved in enerating the 

disturbance also Jeterrnines whether the occurrence will k random or 

permanent. unpredictable or easy lo define. 

tightning surges are the result of direct strikes to the power 

system conductors as well as the result of indirect effects. Indirect 

effects include induction of overvoltages in loops formed by conductors 

round potential rises resulting from lightning current in the soil. 

and A lig % tning strike to the power sysaem -n activate a surge arrester, 

producin a severe reduction or a complete loss of the power system voltage f or one half-cycle. A flashover of line insulators can cause a 

breaker to trip. with reclosing delayed by several cycles, causing a 

momentary power outage. Thus. lightning can be the obvious cause of 

wervotta es near its point of impact, but also a less obvious cause of 

voltage foss at a considerable distance from is point of impact. 

Clearly, the occurrence of this type of disturbance is unpredictable at 

the microscopic level. At the macroscopic level, it IS related to 

geography. seasons. and local system configuration. 

Load switching is a major cause of disturbances. Switching lar e 

R R loads on or off can produce long-duration volta e chan es beyond I C e 

immediate transient response of the circuit. W ether I e swrtching is 

done by the utility or by the user is immaterial from the technical 

point of view, althou h the responsibili may be the subject of a 

contractual dispute. 7%e occurrence of t 1 ese disturbances is somewhat 

predictable. but not necessarily under controlled conditions. The 

mtroduction of power conversion equipment and voltage regulators 

operating by switching on and off at high frequency has created a 

new type of load switching disturbance. These drsturbanccs occur 

steadily, although their amplrtude and harmonic content will vary for a 

given regulator as the load conditions vary. 

Power system faults occur on both sides of the meter. resulting from equipment failure or external causes (vehicle collisions, storms, 

human errors). These disturbances can range from a momentary 

voltage reduction to a complete loss of power lasting for minutes. 

hours, or days. Their accrdental origin makes them unpredictable. although the configuration of a power system and its environment can 

make 11 more or less prone to this type of disturbance. 

NO- loads draw non-sinusoidal currents from the power 

s tem. even if the power system voltage is a perfect sine wave. 

xees currents produce "on-sinuroidal voltage drops in the system source impedance which distort the sine wave produced by the power plant generator. A typical nonlinear load is a dc power supply with 

ca acitor-input filter, such as used in most computers, drawing current 

or!& at the peaks of the voltage sine wave. 
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Characterizing these four rypes of disturbances and disturbance 

mechanisms involves detection (measurement) of their occurrence and 

description of the results of these measurements. What might a pear 

a simple process is in fact made difficult by deficiencies ,n degning 

disturbances observed when making site survey measurements. 

DEFICIENCIES XN DEFLNlTlONS 

One difficulty in coordinating effons for improving power quali 

is that terms used to describe power disturbances are poorly define2 

An effort is bein made by standards writing organizations to resolve 

this problem. as &scribed later in this paper. but consensus has yet to 

he reached, The following two examples of this lack of consensus 

illustrate the point; resolving them is beyond the scope of this paper. 

What is 8 surge? The accepted meaning of surge. in the context 

of power systems, 1s a short-duration overvoltage, typ~cally less than a 

few milliseconds. These mrges are caused by lightning, power system 

switching, or fnults. Protection against them is obtained by protective 

devices called surge arresters (formerly called lightning arresters) for 

utility systems, and surge suppressors, or spike suppressors for enduser systems. This first meaning of the word 'surge' 1s not that 

established by manufacturers and users of disturbance monitors and 

line conditioners. The unfortunate second meaning. a consequence of 

nonexistent standards on the subject. is a momenta overvoltage at 

the fundamental frequency. with a duration of typica?;y a few cycles 

What the designers and users of surge arresters or suppressors calls 

'surge* is called 'impulse' or 'spike' by the monitorin instrument 

community. Fi re 1 shows gra hic descriptions of t e confusion 

created by the duaf?neaning of the worx*surge.' 

f 

What is an outage? Most users agree that it means a loss of 

line voltage. The duration of this event. however. is quite different 

when 'outage' is cited by computer users (as short as one hatf-cycle), 

or by power engineers (seconds, perhaps rmnutes). Funhermore, some 

users and manufacturers of line conditioners do not make a clear 

distinction between corn lete loss of line voltage (zero voltage 

condition). severe undervo P tages ('deep sags'), or the single-phasing of 

plmhase power systems. Part of the problem may be chat the 

definition , of 'outage' has regulatory irnpl~cations for evaluating the 

performance of public utility companies. 

c SURGE 

Figure 1 - Graphic Ufustradon of ditTereat meaning of'surge~' 

and other dbturbaoces 
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As another examplc of definitions deficiencies. standards dictionaries do not define the term 'sag*. Jt is accepted as meaning ;l 

momentary voltage reduction at the ac power frequency. However, 

there is no consensus on the details (threshold, duration, etc.) of what 

characterizes a sag. 

With the present definition deficiencies, manufacturers and uscn 

of disturbance monitors are left without guidance and consequently 

define terms independently from each other. hence the confusion. In 

fact. the development and widespread use of disturbance monitors 

should motivate a more coordinated and rational approach toward 

resolving these deficiencies. Progress in technology of monitoring 

instruments during the last two decades is remarkable and worthy of a 

brief review. 

DISTURBANCE MOMXlRS DEVEXDPMENT HISIDRY 

Historically, the first (unintended) disturbance monitors were the 

actual load equipment. Only later. when confronted with unexplained 

failtires or upsets. did the users start monitorin4 the quality of their 

power systems. Electric utilities have been momtoring the parameters of their systems. but the precise characterization of m~crosemndduration sur es in the early 1960s required special oscilloscopes. For 

the next 1J years. oscilloscopes or simple peak-detectors were the 

basic instruments for monitorin transient overvoltages. Startin in 

the 197% cornrnercia~l~-~roduce! digitizers became available. &nee 

then, technology has made continuing progress as experience has 

accumulated. 

Early site surveys were limited to voltage measurements. This 

limited interest reflected concerns for damage to sensitive electronic 

components connected across the line. Ignormg the im rtance of the 

source impedance led to some performance standards fi that do not 

s cify the current-handling requirements for surge protective devices. 

Eth the introduction and widespread application of new clamping protective devices (silicon avalanche diodes or metal oxide varistors). 

the surge current diverted through these devices became a very 

important factor for proper device selection. Therefore. the need 

emer ed for character~zing current surges as well as volta e surges, 

but k ew surveys to date have addressed this need. This nee% offers a 

challenge and an opportunity to designers of monitoring instruments. 

This challenge has also produced attempts to measure 'energy' 

with an instrument which is actually only a voltmeter. By assigning 

parametric values to the source impedance of the sur e and integrating 

the product (volts . seconds) of the surge, some e nowledge of the 

energy involved would be obtained. Computing true ener . of course. 

requares the measurement of both voltage and current. $;owever. the 

real question concerns the sharing of energy between the impedance of 

the source and the impedance of the load. A discussion of the energy 

in dre surge versus eneqy delivered to the rotective device is beyond 

the scope of this paper. The difference fx tween the two must be 

recognized, however, to prevent further confusion as future monitoring instruments include an 'energy' parameter in their readouts. 
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With the present development of sophisticated multi-channel 

digitizing instruments. future surveys should monitor both voltage and 

current. Note, however, that the current of interesl is that wh~ch the 

surge source would force through a surge protective device. The 

amplitude as well as the waveform of the surges needs to be 

characterized for the correct application of surge protective devices. 

Peak-reading monitors provide useful information on surge activity at 

a given site, but assessment of the surge severity level for the proper 

sizrng of protective devices also requlres waveform and source 

impedance information. 

One difficulty facing users of monitoring instruments in this fastpaced techno10 is that manufacturers are steadily irn rovin their 

mstmments. Rese improved features respond to speci ? rc vis 5, er of 

the users or result from their own product research and development, 

a desirable situation. On the negative side, however, data collected by different instruments become equipment-dependent. Comparison of 

results by third parties is then d~fficult in the absence of " -r dctai s on the instrument characteristics and methods of measurement. 

TYPES OF MO-RS 

The instruments used in past surveys reflect technology progress 

as well as logistics constraints, resulting in a diversity of approaches. Until recently, all monitoring instruments were just special voltmeters. 

Some of the monitors recorded a single parameter. such as the value 

of volta e peaks. or the occurrence of voltage peaks above a preset 

thresholf Other monitors combined time wath voltagc measurements, 

to characterize the voltagc waveforms. The following list shows the 

evolution of simple surge monitors into complex disturbance monitors. 

Threshold counters. - The surge is applied to a calibrated voltage divider. triggering a counter each lime it exceeds a preset threshold. 

The early types had analog circuitry; more recent types have digital conversion of signals. 

Digital peak recorders - The sur e is converted to a digital value 

and recorded in a buffer memory for later playback. In the early 

es of recorders, only the peak was recorded. In later types. the 

Eration of the sur e was also recorded. o ning the way to the more 

complex digital wave p orm recorders now availabr. 

OsciLl05cope with camera - The surge triaers a sin le sweep on 

by an automatic shutterless camera. 

the cathode ray tuhc of the oscilloscope. and IS rccorde 'f as it occurs 

Screen storage oscilloscope - The surge is displayed and storcd on 

the cathode ray tube, and a camera is used for permanent recording 

after the surge has occurred. The writing speed capability of these 

oscilloscopes was a limitation in the late 1960s. 

Digital storage oscillascopc - The surge is digitized ,and storcd in a 

shift register for subsequent playback and display whenever it exceeds 

a preset threshold. An Important feature is the capability of 

displaying events occurring before the beginning of the surge. 
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Digiral waveform recorder - With the advent of compact. portable 

instruments. a revolution hiis taken place in the field of disturbance 

recorders. The earlier surge waveform recorders were large and 

difficult to transport to field sites 131. r). New microprocessorbased instruments have introduced a porta le storage and computing 

wer which has made waveform analysis and graphic display possible. 

thew instruments voltage and current signals are digltired and 

stored, allowing reports of many different arameters of the disturbance. The range of parameters which can & monitored is expanded. 

long trends can be detected, harmonic analysis can be performed. and 

the types of possible measurements art limited only by the creativity 

of the tnstrumtnt designers and the curiosity of the users. 

Although some site surveys might aim at high accuracy, the real 

world experiences an infinite variety of disturbances. making it 

difficult to fil them into simple, orderly categories. Any attempt to 

describe these disturbances in fine de~ail restricts general usefulness 

of the data and can lead to illusions on ap licable accura . Some 

T simple (and ine nsive) instruments are use P ul indicators o '7 frequent 

disturbances. 01 er instruments, more complex (and more expensive), 

rovide comprehensive data on disturbances. A general observation 

goan many sump conduc~ed different researchers is that results 

vary widely from site to site. %us. there is a practical limit to the 

detail hat a sunrey can yield. and unrealistic expectations of precise 

information should be avoided. What is really needed is a more 

uniform and compatible recording and reporting of the data. 

COMPARISONS AMONG StTE SURVEY REPORTS 

Relative occurrence of different trpes d disturbiaas. Two site 

surveys' have been widely cited. One was performed in the early 1970s 

by Allen and Se all [5]. the other in the late 19705 by Goldstein and 

Spersnza 16. Each of these surveys presented results by describing 

various kin J s of disturbances (overvoltages, sags, etc.) and cited the 

percentages of each t of disturbance in the total of all the 

observed disturbances. %e findings did not at fin1 appear to agree. 

raising questions on the likelihood of a change in power systems 

between the first and second survey. However, a detailed comparison 

of these two surveys I]. revealed that the disagreement was rooted in 

a difference of the r C resholds built into the monitors. rather than a 

change in the behavior of power systems. 

Differe- in surge amplitudes. Amplitudes of surges reported in 

several surveys vary over a wide ran e. Comparisons are difficult 

because the reports do not present t I! e data in a uniform format. 

Attempting to get a quantitative corn arison of the amplitudes reported 

seems a futile exercise, because of the fol I' owing reasons: 

1. Lookine at the 'maximum values' cited in the reports. one 

finds that in some surveys this maximum is actually a value 

known only as being above the range of the instrumenr. while for 

others it is the measured value. 

2. Because the threshold of the recorder varies among surveys, 

and the frequency of occurrences increases dramatically with a 

lower threshold. the labels of averal;t, median. most frequent. 

typical. etc.. are not meaningful for comparlng amplitudes. 
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DiFierences in sur e waveforms. What a 't ical* surge might he 

has been the subject Uk many discussions. Severn 'T surveys confirm the 

finding of ringing waves, as o posed to the tradilional unidirectional 

impulses. Elowever, wide dif f crences still cxist among the reports. 

The following examples illustrate this point. 

Mcrrtzfofl-Ifah 17) were amOnf the first to report ring waves, 

recorded by 1960 vintage oscil oscopes. Their findings were 

incorporated mto the data that resulted In the selection of a 100 kHz 

ri, 

wave for the UL Standard Ground Fmh Circuit Intempters [a] 

an the IEEE Guide om Surge Voltages (91. 

CMurbag rurd Smskich 1101 used different instruments recording 

only two points of the woveform: (1) the peak amplitude and time to 

peak, and (2) the time to 50% of the peak amplitude. As such, this 

descri tion is nut a corn Jete waveform. Furthermore, they reported 

that g 0% of their 250, & recordings show the 50% point occurred 

between 900 and 1100 microseconds. This finding is unique among all 

the surveys. 

Wenutmm et oL (11) report ring waves of 500 kHz. bursts of 

fast transients lasting a few microseconds. and even some unidirectional isolated impulses. 

Coedblued I121 is more concerned with interference than damage; 

his report gives emphasis to amplitude, rate of rise. and 'energy'. 

rather than to waveform. 

With the advent of portable monitors capable of presentin the 

digitized data with graphic details as well as summaries, an exp f osion 

in the volume of data can expected. Just the detail and weight of the 

information being collected might swam the researchers, unless data 

reduction procedures are irn Icmented. P Rowever. whenever data reductions are performed by di ferent persons, thcre is a high probabili~ 

that criteria for reduction will be different. making comparisons dil 

ficult, even impossible. Thus, this increased sophist~cation of available 

instrumentation makes coordination even more imperative. The added 

availability of harmonic analysis by rtnble monitors will also lead to 

an expanston of data supporting standar ‘f'=' s on harmonic control [13). 

Agreement and disagreement on rate of occurrence versus levels. 

Several survey authors have attempted to fit a classic statistical 

distribution or a simple relationship between the rate of occurrence of 

surges and their amplitude. The motivation for such a simplified 

presentation might be rooted in a belief that nature obeys simpfe 

mathematical laws. The reality, however, is that so many different 

mechanisms contribute to the generation of surges that a 

f relationship is unlikely. Notwithstandin this rationale. a remnrka si mR'e le 

finding emerges from plotting the resu ts of all the surveys on the 

same ~raph. Figure 2 shows the relative distributions of the findings. 

normahzed for voltage level and frequency of occurrence for each 

survey re ort. The slope of the lines is what can be compared. not 

the abso P ute rale of occurrence. 11 is remarkable that do es are 

relvx is site-dependent. 

similar among the surveys, although the absolute frequency o f occur- 
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8-I - Dub1 L Ymrhmrcot 114) H - Marrrloff & Hahn 

Can - Cannova 171 

1151 

C-S - Coldacrln L Sporarr 161 WSS - Uerns~rom OK al. 

Coo - Coedblood 

r111 

I121 

Clock - point. rc 2 and 

6 kV lor casm history 

rmpartod In ROC 171 

Figure 2 - Rate of surge occurrence 8s 8.iuactioa of peak voltage 

WORKING TOWARD MORE CONSISTENT SURVEYS 

The ambiguities plaguing the field of site surve have become 

a arcnt lo ma interested researchers, resultin in t f e formation by IE~E of a new%orl;in ~roup on Monitorin hetrica~ Quality. me 

scope of r Recommended I rrctice being prepared & this group reads: 

This Recommended Practice concerns the application of 

instruments used for monitoring electrical disturbances on 

power systems. The scope includes the definition of 

disturbance terms, the calibration and connection of the 

instruments, and the interpretation and reporting of the results. 

It does not include specific design aspects of the instruments. 

The disturbances of interest are those conducted on ac power lines for single or polphase systems with direct o ratin 

voltage connections to t e instruments not exceeding k '8 

RMS. De ending on the design of the instruments, the 

duration or the recorded disturbances may range from nanoseconds to many seconds, or more. 

While the prime interest is focused on monitoring low-voltage 

ac power systems (SO, 60 or 400 Hz). suitable interfaces may allow monitoring systems of higher voltage; dc systems Fay 

also be monitored with these instruments. It is also recogn~zed that available instruments may be capable of monitoring other 

arametcrs such as radiated EM1 or environmental conditions; 

!owever, the scope of thir document is limited to conducted 

electrical parameters (voltage, current, and derived parameters). 
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EXPECTATlONS VERSUS RF'i ON POWER QUALITY 

lrnproved credibility of power quality data offers an opportuni 

to revis~t existing standards or develop new standards dealnng wit 

power quality. Three areas would benefit from this review: 

1 

1. More realistic definitions of rhe limits of system voltages. The 

limits currently defined are relatively small percentages (5 to 15%) of 

nominal values, Many anecdotal stories have been told on momentary 

overvolta es exceeding the limits of the only standard addressing these limits. & SI C84.1 (16). Until well documented, these stories can only 

remain anecdotal. However, ignoring them can lead to misapplication 

of surge protective devices by attempting to suppress surges at a level 

tao close to the momentary overvoltages that do occur. 

2 Imprwtd comtosus on Lhc cbafacteristio of surges. The IEEE 

Guide on Surge Voltages (91, dating back to 1980, attempted lo 

simplify the situation by describing the surge environment wth only two waveforms and an upper practical limit. Unfortunately, this Guide 

was misconstrued by some users as a mandatory standard. A revision 

is underway, proposing two additional waveforms and presenting the 

information in a manner that should discourage the misguided use of 

the document as a performance standard. 

3 Im rwcd Consensus on harmonic oontrol. Harmonic causes and 

effects R ave been the subject of many studies and technical papers. but no performance standard exists to settle potential dis Utes between 

rwrcer and receivers of harmonic distortion. The prevaiEng document 

is a Guide (131; significant improvements are expected from a revision 

currently being conducted. 

Power quality measurements. typically performed by site surve s. 

have evolved from the simple mon~toring of surge voltages to t K e 

sophisticated analysis of many criteria of power quality. There is still 

room for improvement in the procedures -- an tmprovement that can 

be guided b voluntary standards. Detailed observation of the issues 

lead to the fol r owing conclusions: 

1. Considerable progress has been made in the recording ca ability of monitoring instruments as the result of progress in the har $ ware and 

software used in digitizing systems. improvements include multichannel synchronized recording of different parameters, fast data 

acquisition, automated data reduction. and improved resolution. 

2. lmprwemeots in consistency must be made, commensurate with 

the steady progress and expanded capability of instruments. This 

greater consistency is needed in the definitions of the disturbance 

parameters and the methods of application of the monitoring 

Instruments. 

3. Site-to-site variations in the occurrence of disturbances revent 

base, 

making precise predictions for a specific site from an overa P 1 data 
4. Diirenots among results indicated by a cursory comparison can 

be resolved by a closer examination of the conditions under which the 

surveys were conductcd. lhwever, some differences are less likely to 

be explained if raw data have ken processed and the initial parameter 

measurements are no longer available for review. 

5. A new WEE Workiig Croup on Monitoring Electrical Quality has 

been formed with a broad scope that encompasses this process of 

improving consistency in definstions and interpretation of ower 

disturbances. In addition, the lEEE Working Croup on Surge C E aracterization is also attemptin to obtain a broader data base for the 

revision of the Guide on Surge b oltqes. 

6. lmprovcd ooopention. promoted by the process of voluntary 

standards development and the exchange of ideas made possible by 

forums such as the Energy Technology Conference, will avo~d some of 

the difficulties on sharing the data PI recited in this paper. This 

paper is presented in sup rt of thls effort and to promote greater 

participation among intereste S" workers and usen. 

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