Event 47988 June 3, 2012 AUTOSTART OF “B” EDG DUE TO LOSS OF OFFSITE POWER CIRCUIT 767
“At approximately 0239 hours on June 3, 2012 the ‘B’ Emergency Diesel Generator (EDG) automatically started when offsite power circuit 767 was de-energized. The EDG started and re-energized Safe Guards busses 16 and 17. The selected Service Water (SW) pump ‘B’ automatically started to supply cooling to the EDG.
“The operators responded to the loss of circuit 767 using abnormal operating procedure AP-ELEC.1 ‘Loss of 12A and/or 12B Busses’.
“Offsite power was restored to 12B bus using ER-ELEC.1 ‘Restoration of Offsite Power’ on circuit 7T at 0318 hours. The ‘B’ EDG was shutdown at 0445 hours.
“The initial investigation of the loss of circuit 767 indicates that the likely cause was due to wildlife, e.g., raccoon.”
A portion of Circuit 767 is run underground in a conduit.
According to Ginna UFSAR Section 8.2, “Different span lengths are employed on the four main circuits with structural anchoring utilized at regular intervals along the right-of-way. In addition, the capacity of any single 115-kV line greatly exceeds
- the power requirements of engineered safety features, which are satisfied by two 2500-kVA diesel generators,
- the auxiliary plant load, which is about 24 MVA, and
- the capacities of circuits 751 or 767, which deliver power at 34.5 kV to the plant.
Circuit 767, one 34.5-kV offsite source, is fed from the 115-kV/34.5-kV transformer 6 at substation 13A and is routed underground to 34.5-kV/4.16-kV transformer 12B at Ginna Station. A voltage regulator was installed on circuit 767 in 1996.”
Comment: This is yet another type of external event that can interrupt Vital Electrical Power. In this case it was necessary for the “B” Emergency Diesel Generator Start and Load its associated Emergency Bus. Attached Drawing shows Circuit 767 and its connection to 12B Startup Transformer.
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