July 21, 2004
By Ed Taylor, Tribune
Investigators think they have the straight poop on what caused the nation's largest nuclear power complex to shut down last month.
Bird droppings.
“There were eyewitnesses,” said Kwin Peterson, a spokesman for the Western Electricity Coordinating Council, which is looking into the Palo Verde nuclear plant incident that caused outages all the way to Canada.
“There was a bird on a 230 kilovolt power line west of Phoenix, and as the bird took off, it let loose as birds often do. The excrement contaminated an insulator, and electricity flashed to the tower, creating a short.”
At the time, utility officials said all three units at the station, plus the natural gas-fired Red Hawk power plant, turned themselves off because of a disturbance in the transmission system. But they did not know the cause.
There was no radioactivity leakage or danger to plant workers or nearby residents, but the loss of the 5,000 megawatts caused short power outages across Arizona to New Mexico, central California and as far as the Canadian province of Alberta.
A final report has not been completed on the cause, but evidence is strong that a bird initiated the incident, Peterson said.
Such incidents happen all the time, he said, but in this case a relay failed that normally would cause a circuit breaker to trip and contain the problem. A backup relay also failed, he said.
A circuit breaker further along the line did trip, but it was so close to the Palo Verde and Red Hawk plants that they had no way to transmit the electricity they were producing, Peterson said. In such a circumstance, the units were designed to automatically shut down.
“A power plant has to get rid of the energy as it is generated, and in this case there were not enough lines available to take the energy being produced,” he said.
The Red Hawk plant was returned to service the same day, and the Palo Verde units were running again within a few days.
Peterson said the electricity council doesn't consider it to be a major incident because most of the 50,000 customers who lost power had it back on within two hours. But a final report due in about two months will make recommendations on how to prevent a reoccurrence, he said.
A spokesman for Arizona Public Service, which operates the Palo Verde plant, declined to comment.
One silver lining in the incident was it proved the Palo Verde plant is capable of doing what it was designed to do, said Mike Gleason, a member of the Arizona Corporation Commission, which regulates Arizona utilities.
“It was the best test we've had to show it does work,” he said.
Contact Ed Taylor by etaylor@aztrib.comemail, or phone (480) 898-6537
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