CSE Pure Power - Fall 2008 - (Page 34)

❯❯ PURE POWER // FALL 2008 34 case study operation. In this case, the 4,000 amp circuit breaker was not equipped with the optional power supply. The circuit breaker and associated trip circuitry were tested and found to be in satisfactory operating condition. Discussions with the manufacturer’s applications support group revealed that using the circuit breaker, without the optional power module, under low load conditions with harmonics present can result in nuisance tripping. The breaker in question was carrying 300 to 400 amps of current at the time of the breaker trips. Also, from the current waveform, it is apparent that harmonics are present. Figure 5 shows the current time plot versus the third, ﬁfth, and seventh harmonics. Both of the trips coincided with lower current levels and slightly elevated harmonic levels. The ﬁfth and seventh harmonics are actually increasing as a percentage of the fundamental, which is a function of the types of loads remaining in operation. Apparently, the unpowered control circuitry responds under these somewhat unusual conditions. The breaker had been in service for quite some time without an incident, and the low current (load) levels were the result of the remodeling activity. This appears to be an example of “Murphy’s Law”: if anything can go wrong, it will. Operating a 4,000 amp circuit breaker at only a few hundred amps is an unusual situation brought about by the remodeling/construction activity, coupled with some load generated harmonics—not all that unusual— and the decision not to implement the breaker’s electronic features on the original installation. These factors created the “perfect storm” for this situation to develop. Once the problem was identiﬁed, then the most cost-effective solution would be to install the power supply for the circuit breaker’s electronics, which should resolve the problem. www.purepowermagazine.com ABOUT THE AUTHOR Lonie is president and a co-founder of PowerCET Corp., Santa Clara, Calif. Previously, he was vice president of ONEAC Corp. and product support manager for the telecommunications division of ROLM Corp. His experience with GTE included operations, customer support, and engineering management positions. A recognized expert in the evaluation of power and grounding problems for the data and telecommunications industries, Lonie has written two books and regularly publishes articles on power quality and the electromagnetic environment. He is co-publisher of PQToday and serves on the editorial advisory board for Power Quality Assurance Magazine. He is a graduate of the University of Redlands, a member of IEEE, and has more than 30 years of experience in computer and telecommunications service and equipment protection. Event details/waveforms 400 200 v 0 -200 -400 AV 300 250 200 150 100 50 0 A Vms (val) 500 250 B Vms (val) C Vms (val) BV CV amps v 0 -250 -500 500 400 AI br : ns . 2 pe Noer o k ea BI CI DI amps 300 200 100 0 A Irms (val) 2:11:41.20 Sunday 2:11:41.25 2:11:41.30 B Irms (val) C Irms (val) 2:11:41.35 D Irms (val) 2:11:41.40 2:11:41.45 Figure 4: Breaker trip No. 2 recorded on Sunday (May 18, 2008) at 2:11 a.m. Source: PowerCET Corp. Time plot amps 1,000 1 No. Trip 700 600 500 400 300 200 100 0 percent 17.5 15.0 12.5 10.0 7.5 5.0 2.5 0.0 A I HG03 Tuesday B I HG03 Wednesday C I HG03 A I HG05 Thursday B I HG05 C I HG05 Friday A I HG07 B I HG07 Saturday A Irms B Irms C Irms C I HG07 Sunday Figure 5: Time plot comparison of load current versus current harmonic content for third, ﬁfth, and seventh harmonic. Source: PowerCET Corp. Trip 800 No. 900 2 http://www.purepowermagazine.com

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CSE Pure Power - Fall 2008 In the News Commissioning CHP Enhancing Emergency Lighting Data Centers for Uncle Sam Handling a Nuisance Trip Sustainable Projects and Partnerships New Products Ad Index

CSE Pure Power - Fall 2008

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