Transformer delays cause stir at ACC meeting

Two transformers being built for the Westwing Substation northwest of Phoenix failed initial tests at the manufacturer, forcing a delay of more than two months in their delivery to the Valley, Arizona Public Service officials said.

At a meeting of the Arizona Corporation Commission on Friday, APS officials tried to assure commissioners and the public that the Valley will still have adequate power supplies this summer.

They said expansion of the San Tan Power Plant in Gilbert, which will add 550 megawatts to the Valley’s power supplies when it’s turned on later this spring, should prevent a repeat of last summer’s electricity crisis triggered by a fire at Westwing.

But several of the commissioners weren’t convinced.

"I’m tense now and will be through mid-June," chairman Jeff Hatch-Miller said.

"I’m very concerned," commissioner Kris Mayes added. "We are looking at a situation with an extremely thin cushion."

The Westwing substation, a critical component of the Valley’s electricity system, was severely damaged in a fire July 4, knocking out six transformers that step down the voltage of power delivered from major electricity generating plants outside the Valley.

Only conservation by consumers and the emergency delivery of a replacement transformer from the Bonneville Power Administration in Washington saved the region from substantial blackouts.

APS officials had expected that replacement transformers for Westwing would begin being delivered March 30 and all would be in place in time to handle the peak loads this summer, when demand for electricity to run air conditioners is highest.

But Friday, they said unexpected problems have developed at the ABB factory near Montreal, where the first two replacement transformers failed tests during the first week in March.

The cause of the problem has been identified, and the units are being fixed, said Jan Bennett, APS vice president of customer service. He said new tests will be conducted on the first replacement unit in about 10 days.

"We are reasonably confident it will pass, but it still must be shipped out here and tested again," he said.

Assuming there are no further delays, the first unit is expected to be operating in mid-June, he said. That unit will replace the smaller, stopgap Bonneville transformer, adding an additional 300 megawatts to the Valley’s electricity supply, Bennett said.

Three more transformers are expected to be operating by mid-July, giving a comfortable margin over the anticipated peak electricity demand, which in most years doesn’t occur until late July and early August, he said. Two more units, one of which is a backup, will be delivered by the end of this year, he said.

Even if, in the worst case scenario, in which no new transformers are delivered to Westwing this summer, the addition to the San Tan plant plus the the new Gavilan Peak Substation north of the metro area will give the Valley an excess of 312 megawatts over the anticipated peak demand of 10,860 megawatts this summer, said Cary Deise, APS director of transmission operations and planning.

Still, he admitted that’s an uncomfortably thin margin. If some other major problem occurs this summer such as a fire at another substation or if wildland fires force the shutdown of a major transmission line, curtailment of electricity service is the only option, he said.

Mayes said she was "a little disappointed" that the preparations for this summer’s air conditioning season aren’t further along. She was particularly critical that planning is not yet completed on improvements to fire protection at Westwing. "It’s almost negligent for APS not to have solved this issue by now," she said.

In an interview, Mayes said the commission will push Valley utilities to "turn over every stone" to find sufficient energy supplies this summer, including making sure existing generators are operating at peak efficiency.