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Significance:

Part 3 – Recorded surge occurrences and surveys

Part 5 – Monitoring instruments

The paper reports an extensive project of monitoring power quality performed with typical instruments 

available in the mid-eighties. Note that during the period of monitoring, the proliferation of low-voltage 

metal-oxide varistors had probably not yet involved all the sites covered by the monitoring. Nevertheless, 

the results indicated that the maximum surges ever recorded in this project had only a 368 V peak. This 

somewhat surprising result needed an explanation.

The discussion offers such an explanation: the monitors that were used for the survey had a built-in 

varistor in their power supply input, a reasonable precaution from the designers of the instrument. With 

hindsight – too late for the researchers – it was realized that the power supply of the monitor was plugged 

in the same receptacle from which the monitored voltage was acquired: small wonder then, that the 

maximum surge voltage that could be observed was simply the let-through voltage of the varistor.

For the purposes of this discussion, only the most relevant pages concerned with surge occurrences have 

been reproduced. The full copyrighted paper is a rich source of data on other disturbances.
ppy

RURAL ALASKA ELECTRIC POWER QUALITY 

3. D, Aspnes, Senior Member, IEEE B. W. Evans, Student Member, IEEE R. P. Merritt, Member IE

Electrical Engineering Department 

University of Alaska 

Fairbanks, A1 aska 99701 

Abstract - Poor quality electric power has traditionally been blamed for electrical and electronic 

equipment malfunctions and failures in rural Alaskan 

communities. This paper reports results of a recently 

completed project in which disturbance analyzers 

provide the first comprehensive power quality data from 

A1 askan v,i 11 ages. 

Power, systems of four widely separated coimunities 

were studied for a total of 1,010 days. These results 

are important because of the trend in rural Alaska 

toward more sophisticated equipment that is sensitive 

to power system disturbances. These data represent a 

first step in developing appropriate countermeasures to 

protect electrical systems connected to isolated rural 

60 Hz power generator facilities. 

INTRODUCTION 

*Increasingly sophisticated electrical and el ectronic equipment is being utilized in small Alaskan 

villages. This ranges from communications satellite 

earth .stations, computers and office equipment to 

controllers and circulating pump motors. The isolated 

qlectric power systems of these communities are almost 

universally supplied by diesel engine-driven generators 

in .the 100 to 1,000 kVA range and are often characterized by small distribution transformers with long 

secondaries. 

Poor electric power quality has repeatedly been 

blamed for electrical equipment malfunction and 

failures, even though data to substantiate this viewpoint were lacking. A project undertaken to remedy 

this lack of data was recently completed and the 

results are reported in this paper. Although extensive 

studies monitoring power line disturbances have been 

~ompleted more than a decade ago [I], the authors 

believe that this paper represents the first 

comprehensive electric power quality data from isolated 

rural Alaskan villages to appear in the open 

literature. Data were collected from four communities 

for a total of 1,010 days. These data help identify 

the scope of the power quality problem in rural Alaska 

and help approach the larger question of what equipment 

is necessary and appropriate to protect in a 

cost-effective way the electrical and electronic 

systems used in remote Alaskan locations. 

SITE IDENTIFICATION 

The process of choosing villages was determined by 

several considerations: (a) reviewing power avail - 

a b i l i t y f o r small earth stations [Z]; (b) Public Health 

84 SM 640-9 A paper recommended and approved 

by the,IEEE Surge Protective Devices Committee of 

the JEEE Power Engineering Society for presentation.at the IEEE/PES 1984 Summer Meeting, Seattle, 

Washington, July 15 - 20, 1984. Manuscript submitted February 1, 1984; made available for printing 

May 10, 1984. 

Service (PHS) circuit ayailabil i ty; (c) 

Aviation Administration (FAA) facility and 

outage reports; (d) accessibility to c

villages; and (e) state facilities availab

placement of equipment. The power availab

earth stations and PHs circuit availabil

categorized into four breakdown causes: (1) 

caused by power; (2) environmental ; (3) eq

and (4) unknown. Two separate lists of c

villages were made; one from the earth stat

and the other from PHS circuit availability. 

The resulting 1 ists included villag

reported the most outages. All four b

categories were weighted equally in the pr

selection. Hence, a village with a high n

outages in one category and low numbers in t

three would not lend itself to candidacy. 

a single list was made by choosing villag

each list that matched in data reported from 

sources, thereby reducing the possib

erroneous data. The FAA reports were c

follows : (1) scheduled maintenance; (2

outages; (3) improvements; (4) power failu

power failure standby; (6) propagation con

(7) weather effects; (8) software; (9) unkn

(10) other. 

The list of candidate villages result

FAA reports was determined in a similar fa

that used for the earth station and PHS 

availability list. The final selection 

data from a1 T above sources. 

This study was primarily concerne

measuring electric power qua1 i ty at user 1 

1 ikely to receive sensitive office automa

computer equipment. Therefore, in three of 

villages the data collecting site was an off

public building. In the fourth site, Amb

were recorded at the service entrance of th

school. In all cases a single phase 120V 

neutral, 60 Hz source was monitored, suppl

four wire grounded wye system. Page lim

preclude a more detailed power system des

All four data collecting sites were in re

modern buildings following National Electri

requirements for wire size and distr

Overvoltage protection was not present at a

The power generating plants and data co

sites were centrally located in all communi

Type and character of electrical loads 

site were standard office equipment, fluores

incandescent 1 ighting, small refrigerato

freezers, circulating pumps. and air 

equipment. The probable maximum individu

rating at any location was less than 10 hp. 

DESCRIPTION OF DISTURBANCE ANALYZER MEAS

CAPABILITIES 

The power 1 ine disturbance analyzers 

in all cases for data collecting were Drane

606-3 units with option 101 (overlunder f

monitoring). They provided the f

information [MI. 

0018-9510/85/0003-0608$01.0001985 IEEE 
Overlunder frequency monitoring to 0.25 Hz 

accuracy. 

RMS voltage level based on a 10 second moving 

average of the measured voltage to an accuracy of 

+1% of reading +I% of nominal input at 60 Hz. 

This is also referred to as slow-average voltage 

in the heading of Table 11. 

RMS value of each AC cycle compared with the 10 

second moving average of measured voltage to an 

accuracy of 21% of reading +I% of nominal input at 

60 Hz. A single-cycle measurement lower than the 

slow average is a sag. A higher single-cycle 

measurement is a surge. 

Transient impulses with duration between 0.5 and 

800 microseconds are recorded to an accuracy of 

+5% of reading rl% of nominal input +6 dB over the 

entire range of impulse width. , 

Outages, defined as loss of line voltage for 

periods greater than 0.5 second, are recorded. 

The disturbance analyzer returns to normal 

operating mode 10 seconds after line voltage is 

restored. 

Saglsurge duration and timing of all events 

including power outages are a1 so recorded. 

The Dranetz 606-3 power line disturbance analyzer 

has isolated circuits for three individual phase 

inputs. These inputs are isolated from each other, the 

internal power supply and ground. In all but one of 

the data sites the only power source available was a 

single phase branch circuit feeding a single duplex 

outlet. For uniformity, the disturbance analyzers were 

in all cases powered by the same single-phase circuit 

that was being monitored. 

There has been concern that the disturbance 

analyzer power supply might affect impulse 

measurements. The units which provided data for this 

paper have power supplies which present a 0.01 VF 

capacitance across the power line regardless of whether 

the unit is turned on or off. This low-pass filter 

type of input circuit is common in household and office 

appl iances. For microsecond pulses (1 MHz), this 

capacitance represents 16 a reactive impedance. This 

impedance would have a small effect on transients 

generated in low impedance sources such as a power 

system having 100 kVA or greater capacity as determined 

by our own laboratory measurements. 

POWER SYSTEM DISTURBANCE DATA SUMMARY 

The following tables and figures present data 

taken during a total of 1,010 days in four remote 

Alaskan communities. The data categories are: 

frequency deviations from 60 Hz, 10 second moving 

average, surgelsag , impulses and known outages. 

Table I shows the number and percentage of days in 

which the maximum power system frequency deviation 

occurred within various ranges for each village and for 

the overall project. A +0.5 Hz threshold for frequency 

monitoring was used at all sites except at Kotzebue 

where the threshold was set at t1.0 Hz. In an effort 

to be consistent with computer manufacturers' power 

system performance specifications, we have reported 

only worst-case frequency deviation data when line 

voltage was within a useable range. Precise frequency 

excursion duration information is not available. 

Table I1 gives the number and percentage of days 

in which the smallest and largest 10 second moving 

average rms system voltage occurred within specified 

ranges for each village and for the total project. 

Reference value is taken to be 120V rms. Thus, the +6% 

to +lo% range corresponds with 127V to 132V; the -13% 

to +6% range corresponds with 104V to 127V; the -20% to 

-13% range corresponds with 96V to 104V; the -40

-20% range corresponds with 72V to 96V; and 

final -100% to -40% category corresponds with 

72V. The slow average threshold voltage settin

all disturbance analyzers was 3V except for the 

at Ambler, for which the threshold was set a

In the case of Kotzebue, there were days in 

the 10 second moving average both rose into the 

to 10% range above 120V and dropped below the 

threshold. Both events were counted independe

giving percentages that do not total 100% and 

which do not sum to the total number of measur

days at that site. This was done to provi

clearer picture of system disturbances. Durati

slow average deviations are not reported he

detail but typically range between one and 

minutes. 

Table I11 provides number and percentag

days in which the worst case sag and surge occ

within specified ranges. These ranges are: 

lo%, 10% to 20% and >20% above a 120V referenc

-20% to -13%, -40% to -20% and -100% to -40% 

the 120V reference. Sag/surge threshold set

were as follows. Ambler: 10V; Fort Yukon: 3V 

40 days, then 5V for the project duration; Kotz

5V; St. Marys: 3V for the first 146 days, the

for the remainder. The maximum surge dur

measured during the entire project for a 

worst-case surge was 231 cycles. Maximum 

duration measured for a daily worst-case sag wa

cycles. Typical saglsurge duration was observ

be less than 40 cycles. 

Table IV shows the number and percentag

days in which the maximum impulse occurred wit

50V to 99V range or had an amplitude greater 

99V. The number of impulses in each catego

given as well as the average of the monthly ma

impulse magnitudes recorded at each location. 

maximum impulse measured at each site is 

included. Impulse voltage threshold at all 

was 50V. 

Table V gives a summary of outage 

Included is the total number of known dur

outages at each data collection site, total n

of outages, total known duration outage 

average outage duration and average number of 

between outages. 

Figures 1 through 4 provide one represen

month of power system disturbance data for 

community included in the study. Included 

daily basis are maximum and minimum frequ

maximum and minimum average voltage, maximum sa

surge voltages, maximum impulse voltage and 

number of impulses (50V thresh01 d) , number of 

and sag duration and number of surges and 

duration (3 to 5V threshold). Thus these fig

give more detailed information than is possib

show in Tables I through V. 

ESTABLISHED LIMITS OF ACCEPTABLE POWER QUA

Several references define acceptable 

quality limits for computer systems [14, 19, 2

for example] and at least one addresses comm

tions systems [22]. General agreement exists 

+6% and -13% rated voltage steady-state limit

necessary, although at least one computer ma

turer is reported to require +4% tolerance 

Opinions about acceptable power quality diffe

transients lasting less than 2 seconds. 

American National Standards Institute (

Standard C84.1 requires +15% and -20% vo

tolerance for transients between 0.05s and 

duration and +20% and -30% voltage toleranc

transients between 0.008s and 0.05s duratio

reported in 1201. A different tolerance envelo

suggested in [I91 resulting from U.S. Navy test
St. Marys (331 

Project Total (1,010) 

5,796 28,278 

88 per day 1 107 per day 1 262v 1 

average average 

23,138 46,463 172V 

64 per day 72 per day 

average average 
y(y, y, )g 

glimpse into an area which few power engineers in the United States see. The problems of rural electric power systems are frequently multifarious, 

including voltage support, frequency control, surge surpression, conductor sizing, and economic operation. The authors have focused on a few areas which relate to siting of specialized, high technology installations. 

Their remarks nonetheless apply to a wide range of rural electrification 

settings. 

I would like to ask the authors whether problems of reconductoring 

and upgrading of components were also considered. Perhaps a table of 

peak load and MWh served annually would be helpful for the reader 

to assess the impact of added loads in the four towns included in the 

study. This question comes to mind since many rural sites have little 

generation margin for expansion. Sites in Latin America, for example, 

often have distribution conductor limitations which would oreclude expansion without considerable expenditure for upgrading capacity. Is this 

also the case in rural Alaska? 

A second area which I would like to discuss concerns the presence of 

harmonics in rural power systems. In many isolated systems of limited 

capacity, loads such as fluorescent lighting and motors with solid state 

controllers cause a significant harmonic distortion. Were tests also made 

in this area? The total harmonic distortion should be considered in rural 

electric systems for which wmputer loads are planned. In our experience, 

a total harmonic distortion greater than 10% (bus voltage) has the potential of interfering with computer timing signals. This has been observed 

at sites in the continental United States and Latin America. 

I would certainly encourage the authors of this paper and others to 

report on other findings relating to rural electric power systems. The 

specialized procedures of design and operation of these systems have been 

neglected in the literature. 

Manuscript received August 2, 1984 

Francois D. Martzloff (General Electric Co., Schenedtady, NY): This 

paper is indeed a very useful contribution to the data base on the occur- - - 

rences of power system disturbances. However, the section dealing with 

the results obtained on the occurrence and levels of "imoulses" might 

still be misleading even though the authors make a referenceto 

the question on the effect of the built-in surge suppressor of the Dranetz 

Analyzers used the measurements. 

The problem arises from a characteristic of the Dranetz equipment, 

which exists for both Models 606 and 626, and which was not recognized at the time the measurements were made but is now pointed out in more recent Dranetz instruction manuals. 

In order to protect the electronics of the Disturbance Analyzer from 

damage by overvoltages in the power supply to these internal electronics, 

a surge suppressor has been provided in the input to the power supplynot to the monitoring input of course. However, if the ac power system 

being monitored is the same as the power system in which the instrument power supply cord is plugged-a likely possibility in the general 

case, and which is precisely situation of the measurements reported in 

the paper-then the observations of surge occurrences on that power 

system are those of a system whose transients have been suppressed! 

To support this claim, Fig. 1 shows an oscillogram recorded at the 

output of a surge generator which provides both 120 V ac power and 

the IEEE/ANSI C62.41 (formerly IEEE 587) ringwave, Category B. The 

oscillogram shows the surge without the Dranetz analyzer plugged in the 

test system output, and, superimposed, the effect of plugging the POWER 

CORD ONLY of the Dranetz analyzer in the test system output. Without 

the analyzer, the open-circuit voltage is 3 kV; with the analyzer plugged 

in, the output voltage is reduced to 1.1 kV. 

The Category B characteristics are 6 kV open-circuit voltage, 500 A 

short-circuit current, therefore a source impedance of 6000 : 500 = 12 

ohms. From the circuit values of Fig. 2, the unknown effective impedance 

of the analyzer, Z, can be computed to be only 7 ohms. The authors 

cite a 16-ohm impedance at 1 MHz; assimilating the first loop of the 

test wave to a half sine wave with a duration of 2.5 microseconds, the 

equivalent frequency in Fig. 1 would be 200 kHz (a period of 5 

microseconds) for which the impedance resulting solely from a capacitor 

would be higher than the 16 ohms at 1 MHz. Thus, it appears that there 

is additional parallel impedance on the line wrd input, since the simplified 

computation of Fig. 2 yields only 7 ohms. That low impedance, when 

Fig. 1. Open-circuit voltage output of KeyTek Surge Generator 

711 with P1 Plug-in and Voltage with Dranetz 606 powe

connected at output of generator. 

Vertical : 1 kV/div 

Sweep : ps/div 

connected in parallel with the voltage measurement leads, will lo

source of the transient and yield lower voltage recordings than 

tual occurrence would have been without the analyzer connecte

situation makes my facetious remark in the 1970 paper [l] com

("the best surge suppressor is a surge monitor!"). 

The authors make the statement that, according to their own lab

measurements, this effect should be negligible on a 100 kVA 

system. That statement seems to imply that there is a correlation b

the 60 Hz impedance of a system (which indeed decreases as th

rating increases) and the effective impedance at the equivalent fr

cy of the impulse; I have some difficulty in accepting that impli

It would be interesting to know the details of the measuremen

by the authors, and compare them to other references, such as t

paper 121 from which Fig. 3 is excerpted. If we accept the valu

by Bull, 50 ohms at 100 kHz, then the 7 ohms effective impeda

the analyzer will reduce the voltage recordings in a 8 : 1 ratio (7

8), regardless of the low 60 Hz impedance of the 100 kVA sys

While it is too late for data already recorded, there is a very 

solution to the problem. Ferroresonant line conditioners not on

vide surge isolation at their output, but also decoupling of the inpu

the output [3]. Fig. 4 shows the open-circuit output of the surge ge

at 6 kV (upper trace) and the output with the line conditioner f

the analyzer plugged in (lower trace). There is no detectable ef

the impinging surge. Thus, by merely inserting the line conditio

the power cord of the analyzer, the issue disappears, and measur

can be obtained without the present ambiquity which can cause 

of false security in the relatively low levels of impulse cited. 

Fig. 2. Computation of effective input impedance of the distu

analyzer power supply. 
J. D. Aspnes, B. W. Evans and R. P. Merritt: We thank the discussers 

for their thoughtful and detailed comments. 

With reference to the questions posed by Dr. Heydt, we recognize the 

problems of reconductoring and upgrading rural systems and the impact of such system modifications on electric power quality. This w z, 

however, outside the scope of the project discussed in this paper. A study 

of economic costs and potential power quality benefits of various system 

upgrades would certainly be a useful follow-up to our initial work. 

Peak load and annual megawatt-hour generation data for the four 

isolated electrical systems are included in Table 1 111. 

Tests to determine presence of harmonics were not done. This would 

also be a valuable addition to future investigations. 

- - REWEICY IYHJ TABLE 1-Utility data 

Fig. 3. Impedance of "Power Mains" as a function of frequency, compared to SO-ohm, 50-uH series combination. (From Ref. [2].) Utility installed Net generation Peak demand 

Location nameplate capacity (kW) (MWH) (MW) 

Ambler 420 348 0.1 

Ft. Yukon 1,050 2,013 0.5 

(estimated) 

Kotzebue 4,825 11,531 2.2 

St. Marys 1,500 1,599 0.4 

Fig. 4. Output voltage of KeyTek 71 1/P1 surge generator. 

Top trace: no connected load 

Lower trace: Line conditioner 

GE Cat 9T91L130G3 

Plugged in output 

Vertical: 2 kV/div 

Sweep: 2p/div 

REFERENCES 

1. F. D. Martzloff and G. J. Hahn, "Surge Voltages in Residential and 

Industrial Power Circuits." ZEEE Trans. on Power Apparatus and 

System PAS-89, pp. 1049-1056, July-August 1970. 

2. J. H. Bull, "Impedance of the Mains Supply at Radio Frequencies." 

Proceedings of the 1st Symposium on EMC, Montreux, 75CH1012-4, 

pp. 357-362, May 1975. 

3. F. D. Martzloff, "The Propagation and Attenuation of Surge Voltages 

and Surge Currents in Low-Voltage AC Circuits" Trans. on Power 

Apparatus and Systems PAS-102, pp. 1 163-1 170, May 1983. 

Manuscript received August 10, 1984 

We turn next to the interesting points raised by Mr. Martzloff. A power 

system impedance function characterized by a parallel 50 ohm, 50 fiH, 

RL network is provided in Fig. 3 of his closure. If this is a true representation of the power systems tested, and if the Dranetz Model 606 analyzer 

may be represented by a 7 ohm impedance, then we agree with Mr. Martzloff's conclusions. However, the resulting 8:l impulse attenuation would 

imply measured averages of monthly maximum impulse magnitudes ranging between 906V and 2944V. Intuitively, these numbers seem excessively 

large. 

To gain some idea of actual impulse attenuation caused by the Model 

606 analyzers used in this project, a Dranetz Disturbance Simulator 

(Model 604A) was used as an impulse generator. We found that the 

unerengized Model 606 power supply attenuated these impulses approximately the same as a 0.01 microfarad capacitor connected across the 

disturbance simulator terminals. A higher energy, lower impedance impulse generator was assembled and a correspondingly lower attenuation 

was noted. 

It would be very interesting to repeat our impulse measurements at 

the original data-gathering sites using a suitably isolated surge monitor. 

However, we have not yet had the opportunity to do so. We again wish to express our appreciation of the discussions which 

have added to the value of our paper. 

REFERENCE 

[I] U. S. Dept. of Energy, Alaska Power Administration, Alaska Electric Power Statistics, 1960-1981, Seventh Edition, August 1982. 

Manuscript received October 25, 1984