FERC questions SCE on transmission line classification

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Southern California Edison is being directed by FERC to provide additional information on its request to have certain 115-kV facilities classified as distribution and not part of the bulk electric system.

After SCE in April asked FERC to determine that some of its 115-kV facilities are not part of the BES, the Western Electricity Coordinating Council and NERC filed comments suggesting the utility address potential reliability issues associated with the possible failure of local network protection systems associated with transformers connected to the facilities.

In its application (FERC Docket No. RC15-1), SCE noted that when FERC approved the definition of the BES, it set a “bright line” that classifies facilities above 100 kV as part of the BES, but those same orders recognized that there may be rare instances with facilities operated above 100 kV are used in local distribution and do not affect the reliability of the BES.

The 115-kV facilities identified in the application are the Devers, El Casco, Mirage, Valley, Victor, Vista and radial facilities north of the Lugo substation. The facilities span about 2,000 circuit miles and include more than 50 substations. SCE, a unit of Edison International, told FERC that the facilities are radial in nature, eliminating the possibility of power flowing into the local facilities and back onto the transmission network. It also said the facilities are not currently classified as transmission and are not under operational control of the California ISO.

SCE indicated that it uses normally open breakers to maintain the radial nature of the facilities, and that it only closes the breakers under emergency conditions using a special “drop and roll” procedure that prevents creating parallel paths with the BES.

FERC on Sept. 2 told the utility to describe the “drop and roll” procedure and to explain how it defines an emergency that would result in the breakers being closed, along with any emergencies over the past five years in which the breakers were closed and a summary of the events.

The Sept. 2 letter from Michael Bardee, director of FERC’s Office of Electric Reliability, also instructed SCE to explain how it will ensure that any faults on the 115-kV facilities will not harm the BES, especially since WECC and NERC expressed concern that the SCE system is susceptible to fault-induced delayed voltage recovery events.

Bardee said a response must be filed within 21 days of the letter.

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