Numerous factors, both human and nonhuman, have caused emergencies in the US power grid in the past, The Washington Post reported Friday.

Random acts such a hawk landing on a power-line insulator, a raging brush fire beneath a wooden power pole, a failed circuit breaker, lightning, tree limbs, and hot weather trigger dozens of emergencies in the nation's power grid each year, investigative reports by the North American Electric Reliability Council (NERC),the power grid's monitor, were quoted as saying.

Human error, faulty planning and violations of operating rules have also been factors, particularly in a small number of cases in which emergencies cascaded into widespread blackouts.

The same mix of factors is likely to turn up as causes of last week's massive power outage from Michigan to New York, according to officials involved in the Energy Department-led investigation.

"My guess is it's a constellation of things," said one official who would not be identified.

The NERC's annual probes into what it calls "system disturbances" for the past three years and its other reports have carried pointed warnings about "preconditions" -- the existence of weaknesses in parts of the power-transmission networks, particularly in the Midwest where last week's blackout is believed to have started.

The NERC warned two years ago that the rapid increase in long-distance shipments of electricity around the country was straining regional control centers that must respond to emergency disruptions.

In its report, the council expressed concern that generating companies might be cutting back on maintenance or operating safeguards in order to improve profitability, as the industry shifted more power deliveries from regulated sales at fixed rates to unregulated wholesale transactions.

In the 58 power-grid disturbances the council reviewed in 2000, including 35 that caused outages, half involved severe weather and12 involved human error either in maintenance or operations.

The NECR report said as systems are being run "closer to the limit" than ever before, the risk of a disturbance precipitating a cascading outage is great. "Unfortunately, it usually takes a system disturbance to highlight weaknesses in the operation of the electric system."

In its assessment of the outlook for power problems for the summer released in May, the NERC warned of a continuing need for power-system operators in states where last week's blackout erupted to coordinate actions carefully because of the risk of large unanticipated power flows through the area.

Referring to the region monitored by the East Central Area Reliability Council, which includes Michigan and Ohio but not New York, the report said the area's transmission system will be more congested this summer than last and parts of it are vulnerable to large unexpected power flows.
 
(Xinhua News Agency August 23, 2003)