Electrical grid tested by the heat

August 1, 2011
| By Pete Daly |
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Consumers Energy, DTE and other Midwestern electricity producers are breathing easier this week after the late July heat wave drove demand to record levels and raised the specter of brownouts in the eastern U.S.

Up to 2,000 Consumers Energy customers in West Michigan were without power at one time, mainly due to overheated transformers.

“That’s out of 1.8 million customers,” said Consumers spokesperson Tim Pietryga. “That’s a percentage we’re proud of.”

From 2 to 3 p.m. Thursday, July 21, Consumers met a record demand of 8,888 megawatts of power, which Pietryga said was the “all-time record send-out” of power in one hour “in the company’s almost 125-year history.”

That afternoon, MISO, which operates the electricity grid throughout all or parts of 12 north-central U.S. states and the Canadian province of Manitoba, appealed to its members to ask customers to scale back their electrical use.

Pietryga said Consumers was not in danger of a brownout due to system overload but “in order to be cautious, in order to be respectful of our neighbors (in other MISO states), we did ask our customers to reduce their use in the afternoon and until about 8 o’clock, if they could.”

Some customers are on an interruptible rate plan, which means they get a discount but agree to allow Consumers to interrupt their service for a limited number of hours if the utility requires extra temporary capacity. However, Pietryga said he was not aware that Consumers actually did that during the worst of the heat wave.

Pietryga said Consumers called some of its largest customers, including business/industrial users, and asked if they could cut back that day “and some did.” He did not identify those customers.

Pietryga said Consumers also kept its line maintenance crews on the job for extra hours that day, until about 8 or 9 p.m., in case there were problems due to the high heat.

“We had some minor issues,” primarily involving overheated transformers in some neighborhoods, said Pietryga.

Some transformers, which step the power down from distribution line voltage to household current, have been in place for 20 or 30 years, he said, and were of sufficient load capacity when installed.

“Over time, we’ve all added computers, flat-screen TVs — this and that,” he said. “Sometimes during these high-demand situations, it does test the limits of these transformers, so in some cases we just have to go into a neighborhood and simply upgrade the transformer.”

Pietryga said he was not sure what percent of the demand during the peak of the heat wave could be attributed to air conditioners, but it might be 30 percent or more.

At least several thousand DTE Energy Co. customers in southeast Michigan were without power at certain times during the heat wave. A DTE executive said the outages were due to local equipment failures, and were not “cascading” or “rolling blackouts.”

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