Generating station returned to service after being damaged by California wildfire

The San Francisco Public Utilities Commission’s (SFPUC) largest hydroelectric generating station was returned to service Sept. 27 following weeks of assessment and repairs after being damaged by the Rim Fire, a wildfire that has burned more than a quarter million acres of wooded land east of the San Francisco Bay area.

“We had testing and then some scheduled maintenance,” after which the Holm powerhouse was returned to service, an SFPUC spokesperson told TransmissionHub Sept. 30. The Hetch Hetchy hydroelectric system returned to its full operating capacity. The system’s Kirkwood powerhouse, which was also damaged by the fire, was returned to service over the Labor Day weekend.

Both powerhouses were taken offline on Aug. 19 when incident commanders asked SFPUC to deenergize transmission lines leading from the powerhouses as a safety precaution for firefighters battling the Rim Fire, which started two days earlier. Ultimately, that fire damaged both powerhouses and knocked out of service a 12-mile stretch of 230-kV transmission that carries the power generated by the power system on the Hetch Hetchy Reservoir to the utility and its municipal customers.

Durng the outage, the utility replaced the power from the facilities that were, and continue to be, out of service by accessing power in an existing power bank and purchasing power on the open market. A third facility, the Moccasin powerhouse, escaped undamaged and generated electricity uninterrupted.

The three powerhouses have a total generating capacity of approximately 380 MW. The Moccasin and Holm powerhouses have two generating units each, with total generation capacity of 100 MW and 160 MW, respectively. The Kirkwood powerhouse has three generating units with a combined capacity of approximately 120 MW. The power is transmitted to San Francisco along city-owned transmission lines and is distributed to the city’s municipal facilities, including its famous cable cars, as well as retail customers, retail city tenants, residences and businesses. In addition to electricity, SFPUC provides retail drinking water and wastewater services to San Francisco, and wholesale water to three Bay Area counties.

The fire also damaged transmission and distribution facilities belonging to Pacific Gas & Electric (PG&E). The blaze damaged 70 poles and 25,000 feet of conductor owned by the utility, but affected service to fewer than 200 customers. The damaged facilities were repaired and returned to service on or before Sept. 5., a PG&E spokesperson told TransmissionHub.

As of midday Sept. 30, firefighters continued to battle hot spots in “isolated smoldering [area] interior to the fire containment lines” for the Rim Fire, according to the fire command’s incident information system. The fire, which is considered 92% contained, has blackened more than 257,000 acres, destroyed 11 homes and 98 outbuildings, and has cost almost $126m to fight. The cause is still under investigation.

PG&E is a subsidiary of PG&E Corporation (NYSE:PCG)