HOUSTON, Sept 11 (Reuters) - Unseasonably hot weather pushed electric consumption in 13 mid-Atlantic and Midwest states on Tuesday to a higher level than in any previous September and forced power to be cut to some customers to avoid a wider blackout, the region's grid agency said Wednesday.
PJM Interconnection, the grid operator from Maryland to Michigan, said Tuesday's power use reached 144,370 megawatts, which broke the previous September record of 129,959 MW, set in 2012.
PJM also said localized equipment problems on Tuesday led to separate power curtailments in Indiana, Michigan, Ohio and Pennsylvania.
Only 154 megawatts were curtailed, a PJM spokesman said. Some customers lost power for about 90 minutes while others were interrupted for as much as 8 hours.
PJM said in a statement it was forced to direct local utilities "to immediately and temporarily cut electricity to some customers to avoid the possibility of an uncontrolled blackout" that would have affected more people.
"Extreme heat in the western region of PJM resulted in record demand for September at a time when many power plants and some transmission lines were off for seasonal maintenance," said Terry Boston, PJM chief executive, in the release.
On Tuesday, about 4,000 MW of nuclear generation was offline in PJM, according to Reuters data.
"Our only option to prevent a potential equipment overload and failures that would cause a much bigger interruption was to call for emergency relief in the form of controlled outages," Boston said.
Chicago's high temperature was 96 degrees Fahrenheit (36 Celsius) on Tuesday, 18 degrees above normal, according to AccuWeather.com.
PJM's highest demand this year was 157,509 MW seen in July, much below the region's all-time record of 163,760 MW hit on July 21, 2011.
Wednesday's peak-hour demand in PJM reached 142,431 MW, according to an initial posting on its website as hot weather lingered.
PJM spokesman Ray Dotter said demand response programs were implemented Wednesday afternoon as demand rose.
Cooler temperatures will trim Thursday's demand to 132,000 MW, according to PJM's forecast.
Next-day PJM West power for Thursday delivery fell 30 percent to the low $80s per megawatt-hour from about $120 the previous day.
Utilities in PJM include American Electric Power Co, Dominion Resources, Exelon Corp, FirstEnergy Corp , Pepco Holdings and PPL Corp.
Detroit's city hall and dozens of public buildings lost power on Wednesday amid soaring temperatures as two of the five main lines that serve the downtown area lost power.