California ISO orders second day of rotating outages

With demand running above forecasts, the California Independent System Operator ordered utilities to shed 400 Mw of firm load in rotating outages at midafternoon Tuesday for the second straight day. The grid operator said the length of the blackouts will be evaluated on an hourly basis and called for conservation to lessen the impact.


By the OGJ Online Staff

HOUSTON, May 8 -- With demand running above forecasts, the California Independent System Operator ordered utilities to shed 400 Mw of firm load in rotating outages at midafternoon Tuesday for the second straight day.

The grid operator said the length of the blackouts will be evaluated on an hourly basis and called for conservation to lessen the impact.

During a briefing, director of grid operations Jim McIntosh said demand was up about 1,000 Mw over Monday thanks to a heat wave and accompanying air conditioning use.

"The main thing is load is running higher," he said, and there is not enough supply in California to satisfy demand. He said the state is receiving about 5,600 Mw of imports.

Southern California Edison Co. said it began cutting load immediately after the ISO's request to prevent a potential widespread disturbance to California's electric transmission grid.

The company said the order was being accomplished by taking groups of circuits out of service on a rotating basis. The initial groups include 71,000 customers in small portions of 59 cities, among them Long Beach, Tulare, Yucaipa, San Marino, Newport Beach, Palm Desert, Santa Monica, and San Bernardino. The outages were expected last up to 1 hr for affected customers, but could be shorter or longer in duration, depending upon circumstances.

If necessary, the process will be repeated with the interruption of a different set of widely scattered circuits each hour until the ISO can sustain reserve levels above 1.5% of energy demand.

Earlier in the day, the ISO issued a Stage 1 emergency indicating reserves were below 7%. A heat spell, including a record 93° in San Francisco, has caused a surge in air conditioning use, McIntosh said. Meanwhile, total of 12,088 Mw worth of generation remains unavailable with power plants off line for maintenance and plant malfunctions.

Four nuclear units are off line in the western US for refueling or repairs. In addition, McIntosh said an additional 2,000 Mw of generation from the state's qualifying facilities (QFs) is unavailable. Peak demand on the transmission system is expected to reach 34,469 Mw about 4 p.m. Tuesday.

More than 88,000 California customers of Southern California Edison and Pacific Gas & Electric Co. were without power for about an hour late Monday afternoon. McIntosh had said he believed the ISO would be able to get through the day without having to ask utilities to cut firm load, but demand stayed stronger than expected throughout the day.

Since January, the ISO has ordered blackouts Jan. 17-18 and Mar. 19-20.

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