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Jan 22 (Reuters) - U.S. federal energy regulators on Wednesday preliminarily determined several companies had violated various reliability standards, causing a blackout in 2011 that left about 2.7 million homes and businesses in the Pacific Southwest without power.
The staff at the Office of Enforcement at the U.S. Federal Energy Regulatory Commission (FERC) did not include any penalties in its so-called notice of alleged violations.
The outages affected parts of Arizona, southern California, and Baja California in Mexico. Some customers were without power for up to 12 hours, FERC said.
The companies alleged to have violated the reliability standards are Pinnacle West Capital Corp's Arizona Public Service utility, the California Independent System Operator, Imperial Irrigation District, Edison International's Southern California Edison, Western Area Power Administration and the Western Electricity Coordinating Council Reliability Coordinator.
The outage started with the loss of Arizona Public Service's Hassayampa-North Gila 500-kilovolt power line that transports electricity from generators in Arizona through the Imperial Irrigation District service area in Southern California and into the San Diego area.
But FERC and the North American Electric Reliability Corp (NERC), which oversees the nation's reliability rules, said in a report in April 2012 the loss of one big power line was not the sole cause of the widespread outage.
The loss of the Hassayampa-North Gila line caused the power flows to move onto lower voltage power lines, creating overloads that eventually resulted in the blackout, FERC and NERC said in the 2012 report.
During the event, FERC and NERC said in the report that the WECC reliability coordinator issued no directives and the transmission operators took only "limited mitigating actions."