CSE Pure Power - Fall 2008 - (Page 32)

❯❯ PURE POWER // FALL 2008 32 400 200 v 0 case study HANDLING A -200 -400 300 250 200 150 100 50 0 500 250 v NUISANCE TRIP By Bruce Lonie, president, PowerCET Corp., Santa Clara, Calif. A Vms (val) THE A sig caus niﬁcant serv ed trips building ice b t reak o a 4,00 remode er. 0 am l p s main 4,000 amp service breaker associated with a research and development facility has experienced a number of unexplained trips. A power monitor was installed on the service to determine if the cause of the circuit breaker’s operation was the result of a fault condition in the building’s electrical distribution, a utility supply issue, or a problem with the electronic control circuitry (trip unit). Because the building was undergoing a signiﬁcant remodel, the general consensus was that there was a wiring problem introduced during the construction activity. A Dranetz-BMI PowerGude 4400 (PG4400) power monitor was connected to the load side of the 4,000 amp circuit breaker. Voltage connections for phases A and C were connected to the utility supply side of the breaker, and phase B was connected to the load side; this conﬁguration ensures that the event capture anytime the breaker trips. LEMFlex RR3035 current probes were installed on the respective phases and neutral to document current levels at the time of event capture. The PG4400 was conﬁgured for crosschannel triggering, i.e., any event trigger will result in all voltage and current changes being recorded. The following is a summary of these lesser events: ◆ Utility sag between 1:30 and 1:40 p.m. on Wednesday ◆ Load sag between 12:30 and 12:40 p.m. on Thursday ◆ Load sag between 4:30 and 4:40 p.m. on Thursday. UTILITY SOURCED VOLTAGE SAG The voltage sag shown in Figure 2 is typical of a utility fault clearing operation. The duration is ﬁve to six cycles, and both the voltage and current decrease indicating a utility sourced fault. Phase C was the most impacted and decreased to approximately 241 Vac during the sag. Most rotating equipment will ride through these types of events, but some electronic loads (tools) may respond the short duration voltage sag. Typical solutions for equipment impacted by these types of events would be some type of voltage regulation or voltage support (uninterruptible power supply or some other type of energy storage device). CIRCUIT BREAKER OPERATION Figures 3 and 4 show the circuit conditions at the time of the two breaker operations (trips). In both cases, the pre-trigger waveform data show no abnormal current surges that would account for the operation of the breaker either from a phase-to-phase or ground fault condition. Zero sum calculations of the monitoring data do not show any signiﬁcant current that could account for the breaker’s unplanned operation. It is as though it (or someone) just turned the breaker off. Based on the data from the two recorded breakers operations, the most likely cause is the breaker’s electronic trip circuitry. The suspect 4,000 amp circuit breaker is equipped with additional control/diagnostic electronics that can provide state and fault conditions on breaker trips. The additional electronics requires an optional power supply to provide the additional functions. The circuit breaker will operate without the additional power supply, but will not provide any state or fault conditions information in the event of a breaker KEY FINDINGS Three signiﬁcant events were recorded during the monitoring period. A graphical summary of the events is shown in Figure 1. Two of the events were associated with a trip of the problem breaker. The other event was a utility sourced sag, most likely the result of fault clearing operations somewhere in the utility distribution system. The following is a summary of the signiﬁcant events: ◆ Event #104 on Tuesday at 8:13 a.m. (see Figure 2) ◆ Event #687 on Saturday at 6:53 a.m., ﬁrst breaker trip (see Figure 3) ◆ Event #808 on Sunday at 2:12 a.m., second breaker trip (see Figure 4). In addition to the three signiﬁcant events, the monitor data revealed other sag-related events, one utility sourced and, most likely, two load turn-on events. These events were not sufﬁcient to cause an event trigger of the PG4400. www.purepowermagazine.com http://www.purepowermagazine.com

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CSE Pure Power - Fall 2008

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