July 25, 2012 / 5:17 PM / 5 years ago

UPDATE 1-US Midwest power demand breaks record due to heat-MISO

* New all-time power demand record at 98,576 MW

* Grid met peak demand with little problem

By Scott DiSavino

July 25 (Reuters) - Demand for electricity in the U.S. Midwest reached record breaking levels on Monday as homes and businesses across the region cranked up their air conditioners to escape a heatwave, the operator of the Midwest power grid said on Wednesday.

The Midwest Independent Transmission System Operator (MISO), which operates the power grid in 11 U.S. Midwest states and the province of Manitoba in Canada, said in a release that electricity usage reached 98,576 megawatts (MW) on Monday afternoon.

That just broke the previous all-time record of 98,526 MW set in July 2011.

For a factbox on U.S. and Canadian record peaks, see

To help keep consumers’ air conditioners humming on Monday, the MISO did not have to take any steps that customers would notice.

The MISO did, however, tell generators and transmission owners not to conduct any unnecessary maintenance during the heatwave, which is a common grid management step also used by other U.S. power system operators during hot weather.

Temperatures in Chicago, the biggest city in the U.S. Midwest, reached 98 degrees Fahrenheit (37 degrees Celsius) on Monday, but dropped to 88 F on Tuesday, according to AccuWeather.com.

On Wednesday, the mercury was expected to return to the 90s again in the Windy City, topping out at about 95 degrees before dropping back to near normal levels in the mid 80s again on Thursday, AccuWeather.com said.

The MISO forecast that demand for power on Wednesday would only reach about 93,000 MW as thunderstorms start to cool parts of the region.

The biggest utilities in the MISO include units of Duke Energy Corp, Xcel Energy Inc, Ameren Corp , Berkshire Hathaway Inc’s MidAmerican Energy, DTE Energy Co and CMS Energy Corp.

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