Case Study Performing Power Quality Studies and Troubleshooting An

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Application Note

Performing powerquality studies and

troubleshooting loads

Working from his offices inPuyallup, Washington, justeast of Tacoma, Mac McArthurperforms power quality stud-ies for commercial, industrial,and residential clients. Healso serves as an agent for

the commissioning of electri-cal systems in new buildingsand the retro-commissioning ofolder buildings.

Prelude to a power-loggerpurchase

In late 2006, McArthur foundhimself in the middle of achallenging assignment. Thesubject of his investigation wasa facility that makes corrugatedpaperboard and whose elec-

trical load was handled by a1,500 kVA transformer ownedby the local utility. The trans-former, a 277/480-volt, 4-wire,Wye, had failed because ofthermal stress with only a 65percent load on it. The util-ity hired McArthur to find thecause of the failure.

“I went in with my basicinstruments, including a single-phase power quality analyzerand my Fluke 189 (true-rms)Digital Multimeter, but I endedup renting an expensivepower logger—a black boxthat allowed me to see whatwas going on, but would notallow me to zero in on just theparameters that interested me,”McArthur explains. That meanta lot of data he didn’t need, fill-ing up the memory too fast. Andwithout a screen on the unit, hecouldn’t verify the setup.

Field Applications

Case Study

Profile: Mac McArthur, power qualityconsultant

Tool: Fluke 1735 Three-PhasePower Logger

Tests performed: Tracing andisolating harmonics; verifyingvoltage drops.

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

Using his instruments and therented power logger, McArthurdetermined that the problemwas on the customer side ofthe transformer. Of course,the utility required that thecompany correct whatever had

caused the transformer failurein order to avoid burning upanother one. So, the companyretained McArthur to diagnosethe problem.

“To put it in numbers,”McArthur says, “the transformeris good for approximately 1,800amps. The company was draw-ing between 1,100 and 1,200amps at full load, but the envi-ronment was full of dc drives.We noticed that dc current was

saturating the transformer’score with all of the equipmenton. This condition was evidentbecause the even harmon-ics were higher in amplitudeespecially the 2nd, 4th and 6th harmonics. Further testingshowed that the transformer’soutput voltage was approxi-mately six to eight volts lowerbecause of the core saturation.That was a problem.”

McArthur started taking read-ings at the service entrances

and went from there down tothe equipment—the individualloads. He found a relativelyhigh dc component beingreflected back to the trans-former and set about to isolatethe source.


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2 Fluke Corporation Performing power quality studies and troubleshooting loads

first, and he recommended itsreplacement. Company officials,however, wanted proof thatchanging out this second drivewould be the final step in

protecting the utility’s trans-former. During the first upgrade,interfacing the new drive andits controller with the existingdie cutter had been a tech-nological challenge, and thewhole project was quite costly.The company did not want torepeat the same process with-out being sure that the upgrade

would accomplish what it wasintended to.

Purchasing a powerlogger

While the initial tests, the firstupgrade, and subsequent testspinpointing the second machinetook place, McArthur looked fora power logger more suited tothis kind of work. He wantedan affordable instrument thatwould provide the baselinefindings he was looking for andprovide concise reports on only

Initially, the consultant iden-tified one drive as a sourceof wayward dc current. Itwas a die cutter’s drive thatwas reflecting a considerable

amount of the second andfourth harmonics back into thedistribution panel and fromthere into the transformer.These even harmonics indicatethe presence of dc. Therefore,at McArthur’s suggestion, plantpersonnel replaced the more-than-20-years-old offendingdrive with a more modern unit.

“We thought that would takecare of the issue,” McArthursays, “but when we started

looking at the main servicescan, we saw that we still had just about the same amplitudefor dc current, indicated by thesecond and fourth harmonics.So, we had to isolate anothermachine as the source of theadditional dc.”

Using the instruments at hisdisposal, McArthur pinpointedthe culprit: another die cutterwith a drive similar to the

the parameters that interestedhim. His search led him to theFluke 1735 Power Logger, anaffordable instrument developedfor consultants like him as well

as plant electricians and electri-cal installers, all of whom haveoccasion to investigate andcorrect disturbances in powerdistribution systems and whowould benefit from owning,rather than renting, a logger.

Not only was the recentlyintroduced Fluke 1735 capableof detecting and displaying theharmonics that were creat-ing havoc in the paperboardcompany’s electrical distribu-

tion system, McArthur sawunlimited potential for it in hiscommissioning work as well asin load studies and energy-useassessments. In addition, theinstrument could capture volt-age events—sags, spikes andinterruptions.

In McArthur’s own words,“The 1735 promised to be veryuseful in harmonics environ-ments. Using the software thatcomes with the instrument, Iwould be able to isolate each

harmonic if I wanted to and doa trend plot or histogram. Buton this particular job, all I hadto be able to do was to see theactual amplitude of the secondand fourth harmonics on thecustomer’s transformer.”

Meanwhile back atthe plant

McArthur obtained a Fluke1735 Power Logger and putit on the main transformer at

the paperboard plant. He thenturned off the suspect die cutterand sampled the electrical envi-ronment. With the die cutternot running, the second andfourth harmonics were essen-tially nonexistent. However,when plant personnel turnedthe machine on, the second andfourth harmonics went fromalmost zero amps to betweensix and 13 amps.


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3 Fluke Corporation Performing power quality studies and troubleshooting loads

“That proved right then andthere that this machine wasour culprit,” McArthur explains.“We needed to have its drivesystem brought up to date using

today’s technology. We hadto get rid of those second andfourth harmonics. We knewthat once those were gone thetransformer would perform theway that it should. And that’swhat happened.”

Finding the cause ofvoltage drops

In another case, McArthurused his recently acquired1735 Power Logger to help a

homeowner place the cause oflights dimming and computerscreen fluctuations squarely onthe shoulders of her electricutility. Because of local zoninglaws, McArthur’s client wasnot permitted to tear down herexisting home to build a newone. As a result, she added3,000 square feet to her home.She uses the addition as herprimary residence while theolder dwelling has become a“mother-in-law apartment” or,in this case, a rental apartment.

The consultant determinedthat the total calculated loadfor the two dwellings is 305amps. The meter base is ratedat 400 amps. However, theutility is supplying the housingunits with only a single-phase25 kVA transformer having afull load rating of 104 amps.

“The problem,” McArthurreveals, “is that she has a four-ton heat pump. Every time the

heat-pump motor starts, thelocked rotor amps (LRA or motorinrush) is 140 amps. When weconsidered the fundamentalload and did the math, it waspretty clear what we weregoing to see when the motorstarted: The lights dim becausethe instantaneous voltage dropwas five or six volts (duringeach episode).”

The client also reports thatdepending on the load on thetransformer, not only do herlights dim but the computerscreen in her home office some-

times shrinks slightly when theheat pump comes on. McArthurexplains that utilities oftenload a 25 kVA transformer upto 200 percent of capacity. Hesays that the loading on thetransformer supplying his clientis more than that—205 or 209percent at peak times.

“I kept telling the utility thatfor a nice steady-state rms loadthey might get away with thisway of operating,” McArthur

reveals, “but any time you injecta motor starter or somethingthat takes an instantaneoushigh current into the system,you are going to see a voltagesag. The sag will manifest itselfin the lights. The utility kepttelling my client, ‘The problem’sin your home.’”

The consultant made anagreement with the homeownerthat he would monitor the elec-trical system at the meter baseto see “what’s being delivered

and what the effects are.” Heattached the power logger fora week’s worth of monitoreddata.

McArthur found that the volt-age sags were averaging threepercent and happening at arate of two to three per hour.McArthur believes that his find-ings will require his client’sutility to address the problemand upgrade the transformer,but he also proposes additional

tests to augment his findings.“The 1735 did a beautiful jobduring the 7-day test,” McAr-thur says. “Using the instru-ment and its accompanyingsoftware, I was able to averageevents over the two-minute,20-second sample period. But Iwant to go back and do at leastone more test.”

McArthur plans either to doone-second sampling for acouple of hours or to sample inthe “event” mode. He explainsthat in his initial sampling,

the interval of two minutesand 20 seconds represented aconsiderable number of cycles.He believes that by using one-second sampling, he will beable to get down to 60 cyclesand “see” the sags in realtime. Then, the sags will, inMcArthur’s own words, “showup deeper.” Regarding usingthe events mode, McArthur saysthat he should be able to setup to detect each sag when it

occurs, with similar results—sags represented as deeper.At this writing, the 1735 is so

new to McArthur that he is stillexploring its capabilities. Still,he anticipates many uses forthe 1735 Power Logger in hisday-to-day work. He is espe-cially interested in the instru-ment’s ability to log powerevery 15 minutes for 30 days,on the same schedule that utili-ties use and the National Elec-tric Code specifies.1

1For details about using the Fluke 1735Power Logger in this way, see the FlukeApplication Note, “30 Day Load Studies withthe 1735 Power Logger”

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Specifications subject to change without notice.Printed in U.S.A. 5/2007 3034602 A-EN-N Rev A

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Case Study Performing Power Quality Studies and Troubleshooting An