PG&E: Bucks line was scheduled for hardening

The Pacific Gas and Electric Company responded to more questions Wednesday from United States District Judge William Alsup concerning the Bucks Creek at 1101 circuit that is suspected of causing the Dixie Fire in July.

Alsup continues to press the company on why it did not shut down the entire line on the morning of July 13, when the line lost power. In Wednesday’s response, the company offered a further explanation to a question Alsup asked in mid-November that after learning at 2:43 p.m. on July 13 at least one fuse had blown and the company was going to have trouble reaching the fuse, and that there was limited cell and radio service from the site — what did the operator think was causing the outage or what possibly could have caused the outage? And could that cause make it prudent to cut the power?

The company noted that the operator was an apprentice who was being supervised by a more experienced operator who the company says listened to the phone call at 2:53 p.m. that day.

In that phone call, the Dixie troubleman told the operator that he saw at least one open fuse but had not yet been able to reach the fuses. The more experienced operator, which court filings referred to as operator No. 3 thought the cause of the power outage was the open fuse condition described by the Dixie troubleman.

But the operator said he did not know the cause of the open fuse condition, however, he told the court in his experience the operation of one or more fuses is a routine event and is not in itself a reason to de-energize the line and cut off power to all users.

According to the filing, “The operation of fuses is designed to end fault events by preventing current from continuing downstream from the source on the conductors experiencing the fault. In NDCC Operator No. 3’s experience, there are numerous potential causes of fuses operating, with the most common being faults caused by birds, squirrels, tree limbs falling, tree contacts, the wind blowing lines together and other similar events.”

The company also said that at about 2 p.m. when operator No. 2 briefed him about the line, which was about an hour before the troubleman’s call, operator No. 3 did not see in the real-time data any indication of a ground fault or anything in the data indicating a reason to de-energize the entire line.

In mid-November, in response to a question by Alsup on how Bucks Creek 1101 Circuit was ranked 11 out of 3,635 circuits with respect to the Equipment Risk, the company said that about seven months before the fire it had determined that the line was in need of hardening.

That work was set to begin in 2022.

The company said in the filing that the 2021 model that came up with the ranking assesses the risk of wildfire ignition, spread and consequence associated with equipment failure related to the approximately 25,000 miles of overhead distribution conductor facilities in the High Fire Threat Districts Tiers 3 and 2.

According to the filing, “the Equipment Risk Model is comprised of two sub-models: one that produces a Probability of Ignition (“POI”) from equipment failure, and a second that simulates the Consequence of Ignition (“Wildfire Consequence”).”

The company says considers these to be the components of the wildfire risk formula: Wildfire Risk equals Probability of Ignition times Wildfire Consequence.

“The Probability of Ignition for each CPZ is derived using a machine learning regression model to examine a number of covariates, or variables, associated with PG&E’s overhead distribution conductors, and environmental and weather conditions in the specific area where the conductor is located, against known historical ignition events to produce a relative occurrence rate, i.e., a Probability of Ignition.”

The Bucks Creek 1101 had an ignition rating of 181 according to PG&E which said that it for that ranking because of its low precipitation average, copper made conductor material used on the line which has a higher likelihood of failure relative to other conductor material, and the maximum tree height in the segment.

The company also noted that the size of the 44-year-old conductor was also a factor.

Because of the 2021 risk rank, PG&E identified the Bucks Creek 1101 as a priority for system hardening and quickly began to develop a plan to harden this circuit, which was approved in January 2021.

But the company also said that due to various factors, including weather and multiple agency dependencies (including railroad, Caltrans, U.S. Forest Service, Cal Fire, and local counties), the project was slated to start construction in 2022.

To get the Wildfire Consequence estimation in the 2021 model, the company said it uses “the Technosylva fire modeling simulation software to estimate fire propagation in terms of rate of spread, flame length and fire intensity known as fire behavior index; and wildfire consequence in terms of estimated acres burned, structures impacted, and population impacted using an 8-hour fire simulation (assuming no suppression) based on estimated ground fuel conditions and historical elevated fire weather conditions.”

The company says it takes these “natural units” and converts them into a multi-attribute value function score in line with the company’s 2020 risk assessment and mitigation phase report and the 2018 safety model assessment proceeding settlement agreement.

That simulation output scored the area occupied by the Bucks Creek 1101 as 3,512 multi-attribute value function points which was ranked at 200, driven by elevated acres burned and fire behavior index score.

The company says it the overall risk score was calculated by multiplying Probability of Ignition (0.000265) by Wildfire Consequence (3,512) to produce a overall risk rank in the 2021 Equipment Risk Model of 11 (of 3,635 circuit segments).

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