Over three years, GRU witnessed four or five similar events and all of these events were related to a faulty capacitor bank switching. However, because the evidence obtained from the field was inconsistent in all of the previous events, the utility could not positively identify the root cause of these transients; it could, however, verify that they all exhibited similar conditions.
The suspected transients captured by PMI's Eagle 330 PQ recorder may have been caused by a bad batch of vacuum switches, bad connections or bad cutouts. After further investigation of a failed capacitor bank by qualified personnel, it was determined that A & B phase arrestors had blown, and B phase insulator on the main line had been burnt and had to be replaced.
It was clear and safe to assume the capacitor bank was hit by some voltage surge, possibly lightning. And, with a high degree of probability, the transient overvoltage caused by the switching capacitor bank resulted in the MCC B&C fuses to blow. None of this analysis and investigation would have been possible without the use of the Eagle 330 portable power monitor...
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