Substation disturbance reported minutes before Woolsey Fire ignition in California

Southern California Edison reported to state regulators that a circuit at its Chatsworth Substation, located just south of Simi Valley, California, "relayed" at 2:22pm on Thursday 8 November 2018, meaning a sensor detected a disturbance and switched the circuit off. Cal Fire said the Woolsey Fire is believed to have started about two minutes later, at approximately 2:24pm, in the area of Alfa Road south of Simi Valley. The utility said it was not clear whether the disturbance contributed to the fire, whether the fire caused the disturbance, or whether the two were unrelated, and that crews had not been able to access facilities in the area where the fire began. It added that there were no signs at that stage that its infrastructure caused the blaze. The source reports the fire had by then burned about 70,000 acres, forced some 200,000 people from their homes and destroyed an unknown number of structures across Ventura and Los Angeles counties. The California Public Utilities Commission said it would incorporate the report into its assessment of compliance of electric facilities in fire-affected areas.

A sensed electrical disturbance on a circuit tied to the substation triggered a protective relay and an outage shortly before the reported fire start time. The cause of the disturbance had not been identified at the time of reporting, and no link to the fire had been established.

1. Utilities operating in wildfire-prone areas should report equipment anomalies to regulators promptly when they coincide in time and place with nearby ignitions.
2. Coincidence in timing is not evidence of causation, and independent investigation is needed before any cause is attributed.
3. Restricted access to fire-affected infrastructure can delay damage assessment and root cause work, so remote monitoring and inspection capability has value.

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