Pacific Gas and Electric Company Issues December 8, 1998 Outage Investigation Report.
PG&E's internal investigation has confirmed that the outage resulted when a construction crew working on an equipment upgrade project at the San Mateo Substation failed to follow established procedures and practices, and improperly removed temporary protective grounds. Separately, a transmission operator at the substation then energized the lines, but failed to engage the protective relays associated with the lines. Without the local protective system in place, the electric current was sent to ground, and the system took a half second to isolate the fault instead of the one-tenth of a second that would normally be required.
This delay resulted in a sharp drop in transmission line voltages, and the transmission system into San Francisco then experienced large power fluctuations. As they are designed to do, protective systems at other substations and at the Hunters Point and Potrero power plants separated from the transmission system to make sure that the fluctuations did not extend to other parts of PG&E's system, and that no damage occurred to equipment in San Francisco's electric facilities that could have delayed restoration of operations.
"Over the past six weeks, we have conducted a thorough review to identify what went wrong," said PG&E President and CEO Gordon R. Smith. "Our study has confirmed that it was a combination of the failure to follow procedures and miscommunications. As I have said previously, there is no excuse for what happened, and more than inconveniencing our customers, we feel we did not live up to our own high standards for delivering service reliably and safely."
The utility's investigation has found that the restoration effort generally proceeded smoothly, and given the scope of the outage, was completed in a reasonable time. Some customers were restored in as little as one hour, and most were restored within six hours.
PG&E has worked and communicated extensively with the California Independent System Operator (CAISO) from the outset, immediately notifying the CAISO of the outage. PG&E and the CAISO are using the lessons learned in this event to strengthen their communications.
The investigation has also found that the transmission system design is consistent with the requirements of the North American Electric Reliability Council and the Western Systems Coordinating Council, and performed as designed given the initiating event that occurred. As a result of this finding, the company is not proposing modifications to the system design. Rather, actions PG&E is taking are focused on preventing such an initiating event.
The executive overview of PG&E's December 8 outage investigation report can be found on the company's website at www.pge.com. In addition, PG&E is filing a similar report today in response to a request by the California Public Utilities Commission.
For more information about PG&E, please visit our web site, http://www.pge.com