A recently released report by the California Public Utilities Commission concluded that the power outage and subsequent flareup at the Valero Benicia Refinery in May 2017 was the result of a failed electrical unit at Pacific Gas & Electric’s substation and the lack of adequate staff training over the component.
(File photo by Ashton Lyle)

A report by the California Public Utilities Commission said the power outage at the Valero Benicia Refinery which led to a flareup and shutdown of the Industrial Park in 2017 was the result of a failed voltage transformer at Pacific Gas & Electric’s (PG&E) Bahia Substation and not providing adequate training or documents related to the component.

On May 5, 2017, an 18-minute power outage occurred at the refinery. When power was restored, a plume of black smoke was released, prompting an evacuation of the Industrial Park and the establishment of shelters-in-place at nearby Robert Semple and Matthew Turner elementary schools. An August report by the Solano County Environmental Health division said the flaring was partly a result of a soot buildup from steam boilers not operating during the outage. A few months after the incident, Valero filed a lawsuit against PG&E, and the case is still ongoing.

Additionally, numerous government agencies have been investigating the cause of the incident.

In April, the CPUC completed an eight-page incident investigation report which was recently made available to the public following a public records request and subsequent article by KQED. The report determined a failed coupling capacitor voltage transformer at PG&E’s substation to be the culprit. The author of the report noted that the transformer “in conjunction with a planned maintenance operation at the substation caused the anti-islanding protection scheme at Valero Substation to operate” and “the operation of the protection scheme disconnected the refinery from PG&E’s Bahia Substation resulting in the subsequent loss of power.”

PG&E’s Bahia Substation is fed by two 230 kilovolt circuits, the Vaca Dixon-Bahia and the Bahia Moraga, according to the report. The CPUC laid out a timeline of events leading up to the May 5, 2017 incident provided by the third-party firm Exponent. Between May 1 and 4, the Bahia Moraga circuit had been de-energized for planned work on transmission towers, which Valero was notified of on March 2. The Moraga circuit was slated to be re-energized by 6 p.m. May 4. Station staff determined there was a filed transformer. An operator reviewed a single-line meter, relay diagram and description document for the anti-islanding protection scheme and found no protection was jeopardized by the failed transformer. The operator notified the substation maintenance and operations of the failed transformer and re-energized the Moraga line. At 5:49 a.m. the next morning, PG&E began its scheduled switching of the de-energized Vaca Dixon-Bahia, which Valero had been notified of on March 6. As routine switching was being performed at 6:40 a.m. sustained interruption occurred, resulting in loss of power.

Exponent provided five safety measures to prevent a similar incident from happening in the future, including adding Emergency Medical Services line-item alarms, performing regular reviews of anti-islanding scheme description documents and providing regular refresher training to operators.

The report said that PG&E violated General Order, Rule 12, which states that, “Substations shall be designed, constructed and maintained for their intended use, regard being given to the conditions under which they are to be operated, to promote the safety of workers and the public and enable adequacy of service. CPUC charged that PG&E violated this rule because it did not maintain the transformer for its intended use and did not provide proper training, documents or diagrams to allow operators to fully understand the anti-islanding protection scheme.

“If the Bahia Substation operators had sufficient training and documentation on the anti-islanding protection scheme, they would have properly identified and resolved the failed (transformer) and prevented the issue from occurring,” the report noted.

In an emailed statement, Valero spokesperson Paul Adler said the refinery supported the findings of the CPUC report, as well as similar conclusions made by Solano County’s environmental health division and Cal/OSHA.

“Every public agency that has reviewed the incident has reached the same conclusion — that PG&E is solely responsible for the May 5, 2017 power outage,” Adler wrote. “It is not enough for PG&E to implement corrective measures after the fact. It is time for PG&E to accept the CPUC’s (and previous) findings and take full responsibility for the lack of training and procedural errors which caused the power outage, resulting in damages to the refinery and alarming the surrounding community.”

However, Deanna Contreras– a spokesperson for PG&E’s North bay division– felt Valero was still at fault.

“PG&E denies the CPUC’s specific allegations that we failed to maintain a type of transformer for its intended use and that we failed to provide adequate training, documents or diagrams to operators,” she wrote in an email. “Additionally, PG&E maintains that the responsibility for the unplanned refinery shutdown rests with Valero.”

Contreras said the company continues to apologize for the outage and was following through on Exponent’s recommendations as well as other corrective actions.

“We take every outage seriously and we’re focused on making sure that something like this doesn’t happen again,” she said.

To read the full report, go to assets.documentcloud.org/documents/4613939/CPUC-PGE-Valero-Investigative-Report.pdf.

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