Sweating it out at NStar

Few people in Boston were feeling the heat yesterday more than Werner Schweiger and Larry Gelbien .

The two are top NStar executives who oversee the utility's Boston command center, where the ultimate responsibility lay for keeping the lights and air conditioning on as hot weather drove demand for electricity to a record high.

Most days the Massachusetts Avenue facility, whose front wall features a 200-foot-wide schematic diagram of all of NStar's major power lines, is quiet, with technicians mainly waiting for alarms to flash on computer screens about overloaded circuits and broken-down transformers.

But facing the most intense strain on its system in history, Schweiger, NStar's senior vice president of operations, and Gelbien, its vice president of engineering, had a half-dozen engineers on duty all day at computer consoles checking power-line loads and ordering switches flipped to keep demand from overwhelming the NStar grid.

Across NStar's service territory, which includes 1.1 million homeowners and businesses in Boston and 80 Eastern Massachusetts communities, the utility was taking other extraordinary steps to keep the lights on.

Four hundred extra line crew workers were called in, some off vacations, to tackle any blackouts, on top of the normal 1,100 scheduled workers. Helicopter crews flew by high-voltage lines on a special inspection looking for potential trouble spots. For the first time , NStar used an automated, pre recorded phone-message system to call 700,000 customers with tips for saving energy, like turning up the air conditioner thermostat and covering windows with drapes to keep rooms cool.

``I know this is going to be a rough week, but it feels like we're getting through it pretty well so far -- and I hope I don't have to eat those words," NStar chief executive Thomas J. May said yesterday during a visit to the utility's ``war room."

At various times in the past two days, NStar crews worked on outages affecting between 5,000 and 10,000 customers, but many were blackouts that had nothing to do with the heat, including construction crews hitting underground power lines, squirrels short-circuiting equipment, or motorists crashing into utility poles.

As temperatures soared to 98 degrees at Logan International Airport in mid afternoon and touched 100 elsewhere in New England, regional power grid officials appealed to consumers and businesses to shut off lights and appliances.

Shortly after 1 p.m. they also ordered a 5 percent voltage reduction, or reduction in regional electric output, to stretch supplies, which New Englanders could see showing up as dimmer lights, slower-opening electric garage doors, and slightly smaller television screen pictures.

Demand for electricity hit 28,021 megawatts between 2 p.m. and 3 p.m. yesterday, a record that was 620 megawatts above the previous high set a day before. Dozens of businesses, institutions, and government agencies that participate in so-called demand response programs that pay them money to curb electric use on the hottest days of summer were called upon to restrict use, according to Consumer Powerline and EnerNOC , two companies that manage the programs.

The increase in power demand from Tuesday to yesterday -- driven overwhelmingly by air conditioning and refrigeration systems -- was the equivalent of 460,000 normal-sized homes suddenly appearing in New England.

At Constellation NewEnergy Inc., a Boston energy services company in the Prudential Tower, employees shut off their office lights and worked by computer glow and daylight to help the grid stretch out available power supplies, a company spokesman said. In a worst-case scenario, grid officials would have to impose rolling blackouts if electric demand were to exceed supply.

For NStar, maintaining balance between electric demand and supply yesterday meant doing a whole lot of little things. With Cape Cod facing a particularly tough power pinch, the utility called up the Otis Air National Guard Base and asked commanders to switch over to their own generators for the afternoon, Schweiger said. That freed up between 2 and 3 megawatts of electricity, enough to cover demand from about 2,000 homes.

Throughout the day, Gelbien said, engineers yesterday were manually rerouting about a half-dozen power circuits, or feeder lines, that bring electricity to towns and neighborhoods. For virtually all service areas, NStar has at least two circuits it can use to deliver power. Scrolling through computer screens, engineers were at work identifying feeders close to being overloaded, then consulting line diagrams to figure out how to switch clusters of customers to less-taxed power circuits.

In most cases, that process can be done through a radio signaling system that opens and closes circuits, but in several locations engineers were still calling crews to physically pull switches.

``There's a lot of scrutiny today around what every feeder and every transformer is doing," Schweiger said. ``The whole idea of it is to stay ahead of what's happening out there."

Peter J. Howe can be reached at howe@globe.com.