Steps Being Taken To De-Energize Transformers Found To Have Moisture In Oil
San Francisco - As a precautionary measure, Pacific Gas and Electric Company is de-energized five transformers in downtown San Francisco with elevated levels of moisture in the oil contained in the high-voltage chambers attached to the transformers. Independent laboratory tests of oil samples taken from these transformers determined the presence of moisture above levels the utility believes are prudent for normal operation.
Although moisture content in the five samples were at levels that are unlikely to lead to immediate failure or pose a risk to the public or to PG&E employees, PG&E decided to disconnect all five transformers today and is replacing the oil in these primary chambers, to ensure continued safe operation of the transformer equipment.
No customers are expected to lose power as a result of this work. PG&E crews expect to replace the oil and return these five transformers to service tonight, but if not, they can remain de-energized without causing customer outages, if necessary to complete the process.
PG&E will conduct additional testing and examination of these high-voltage chambers to determine the source of moisture intrusion and make all repairs necessary to prevent it from occurring in the future.
The oil testing program of 1,115 transformer high-voltage chambers was launched by PG&E as soon as it learned that moisture intrusion into the oil of the chamber was the cause of the August 19 underground vault explosion at Kearny and Post streets in San Francisco. The independent expert PG&E asked to lead this investigation found that moisture had gradually entered the transformer's oil-filled high-voltage chamber due to an improperly seated gasket. Over time, the moisture levels rose to the point that the oil no longer properly insulated the energized equipment in the chamber, which lead to arcing and eventually a short circuit.
PG&E began this oil testing program two weeks ago, and expects to complete the effort in approximately eight more weeks. PG&E has committed to taking similar action as it has today, should its ongoing testing of the remaining high-voltage chambers reveal elevated levels of moisture in the oil.
SOURCE: Pacific Gas and Electric Company