* Power grids do not expect demand to break records
* Some demand response programs activated
* Temperatures to reach near-record levels in mid 90s F
June 20 (Reuters) - A heat wave blanketing the U.S. Mid-Atlantic and Northeast on the first day of summer forced utilities to ask customers to conserve electricity and led to brownouts in parts of New York City.
Electrical grid operators said they expected to have more than enough power resources to meet soaring demand on Wednesday and Thursday in New York, New England and the 13 states served by regional transmission organization PJM.
The New York grid operator revised its power consumption forecast for Thursday, saying its new forecast of 33,700 megawatts would exceed last summer's peak of 33,295 MW.
Temperatures in New York City, the biggest metropolitan area in the United States, were expected to reach a near-record high of 96 degrees Fahrenheit (35.6 degrees Celsius) on Wednesday, 97 degrees on Thursday and 92 on Friday before dropping to the 80s over the weekend. The National Weather Service issued a heat advisory until Thursday night.
Average highs in New York at this time of year are about 81.
New York's Consolidated Edison Inc reduced electric voltage on some equipment in Queens and Brooklyn Wednesday evening.
The reduction, called a brownout, is used to protect equipment and maintain service while crews worked on the problem, the power distributor said in a release.
Con Edison asked customers to conserve electricity and turn off nonessential equipment. Customers don't lose power in a voltage reduction, which primarily affects incandescent lights, hot water heaters and some motors.
The New York Power Authority (NYPA) and the New York Independent System Operator activated demand response programs in the city and parts of the state Wednesday afternoon to curb peak demand.
PJM issued a hot-weather alert for both days, telling generators and transmission owners to put off unnecessary maintenance on their plants and power lines until after the heat wave passes.
PJM is the biggest power grid in the United States, serving 60 million people in much of 13 Mid-Atlantic and Midwest states.
Regional grid operator ISO New England also said it expected normal operating conditions and asked transmission owners and generators to delay unnecessary work, spokeswoman Marcia Blomberg told Reuters.
ISO New England also said it was aware of maintenance on Spectra Energy Corp's Algonquin Gas Transmission natural gas pipeline, but added that the power grid was still operating under normal conditions.
For competitive reasons, the ISO could not say whether any power plants had their gas supplies interrupted.
Spectra said on its website that the maintenance was affecting some interruptible customers who typically pay less for gas with the understanding that service may be cut at certain times.
The PJM grid did not expect to activate demand response or energy conservation programs, spokesman Ray Dotter said, but noted some local utilities or power marketers might ask customers to reduce their power use.
In Pennsylvania, utility regulators urged consumers to cut back on energy usage over the next couple of days.
NYPA said it had activated a demand-response program called Peak Reduction to reduce demand in New York City by 30 megawatts Wednesday for as long as six hours.
NYPA's government customers will lower electric use at about 80 locations in the five boroughs, including subway stations, public schools and police facilities, according to a release.
NYPA also said it might activate the program again Thursday.
Demand-response programs like NYPA's cause minor inconveniences - hot subway cars, longer waits for elevators and darker office lobbies - but utilities say they keep the lights on and air conditioners humming for everyone as well as keep power prices from climbing too high.
Besides reducing usage, demand-response participants can run onsite power generators to take the load off the grid.
Power prices in PJM, the most active hub in the United States, jumped about 70 percent on Wednesday to the $150s per megawatt hour for Thursday delivery. New England prices jumped almost 80 percent to the $170s for Thursday.
RECORDS TO BE TESTED
The New York ISO, which operates the state's power grid, said Wednesday's demand was approaching 31,500 MW and raised Thursday's projection by 800 MW to 33,700 MW which would exceed last summer's record and approach the all-time record of 33,939 MW set in August 2006.
PJM expects demand for power to peak at just under 150,000 MW on Wednesday and a little higher Thursday, well below the all-time high of 163,760 MW set during a heat wave last July.
ISO New England, which operates the grid in the six New England states, forecast peak demand 22,760 MW on Wednesday and 25,320 MW on Thursday. That is well below the all-time high in New England of 28,130 MW, also set in August 2006.
The biggest utilities and generators in the Northeast include units of Illinois-based Exelon Corp, Ohio-based FirstEnergy Corp and American Electric Power Co Inc , North Carolina-based Duke Energy Corp and New York-based Con Edison Inc.