PJM believes isolation of power system was automatic

The operator of the power grid in Pennsylvania, New Jersey and Maryland said automated controls shut down some high-voltage lines on Aug. 14, sparing millions of customers from the blackouts of neighbouring states.
Lines connecting the PJM Interconnection transmission system to FirstEnergy's in northern Ohio and Consolidated Edison's in New York were shut by pre-programmed devices called relays, said Robert Hinkel, a general manager at PJM. The devices were triggered at 4:11 p.m., about the same time that blackouts cascaded across the eastern US and Canada, he said.

At least one power-line owner has said uncoordinated shutdowns of lines by utilities that escaped the blackout may have caused the failures to spread, contributing to the biggest blackout in North American history.
"I personally don't believe the separation of our system is why theirs collapsed," Hinkel said at the group's headquarters campus in Norristown, Pennsylvania. "Our equipment operated automatically, with no manual intervention." Without PJM's relay triggers, "more systems would have collapsed," he said.

What's still not clear is what caused the power lines to fail, Hinkel said. PJM is conducting an internal investigation in conjunction with a broader probe led by US Energy Secretary Spencer Abraham and his Canadian counterpart, Herb Dhaliwal. The blackout spread across eight states and Ontario and knocked out 61,800 MW of power demand, or enough electricity for about 49 mm average US homes.
Officials with the North American Electric Reliability Council, which is coordinating the power industry's portion of the investigation, have said the cascading blackouts probably began with a series of transmission-line failures on FirstEnergy's grid in northern Ohio, near Cleveland. One of the lines short-circuited after overheating and sagging into a tree.

FirstEnergy, based in Akron, Ohio, has acknowledged the failure of a power plant and four transmission lines on its system in the hours before the blackout, while maintaining that failures occurred elsewhere in the eastern US Industry officials and experts have assigned a range of underlying causes to the blackout, from the lack of investment in new high-voltage lines to regulators being unable to enforce reliability standards. Joseph Welch, CEO of International Transmission, owner of eastern Michigan's power grid, said in a hearing that uncoordinated shutdowns of lines by utilities trying to protect their systems were the "tsunamic action" in the blackout.
"We've yet to get to the problem of why the system was so vulnerable that day," said Lawrence Makovich, a senior director at Cambridge Energy Research Associates, a Massachusetts-based energy consultancy. "We had some normal component failures, but we had an inability to respond either automatically or with human decisions to contain this problem to a small area."

About 4,500 MW of electricity demand were lost in the PJM service area, representing about 7 % of total demand on the system just prior to the blackout, according to the group. Homes and businesses were darkened in Public Service Enterprise Group's grid in north-eastern New Jersey and FirstEnergy's grid in north-western Pennsylvania.
PJM's line failures prevented the blackout from affecting customers of Pepco Holdings in Washington, Exelon in Philadelphia and Constellation Energy Group in Baltimore, Hinkel said. Also spared were the electric systems of Maryland-based Allegheny Energy Inc. and FirstEnergy's utilities in central and north-western New Jersey.
"People have been asking us, `Why did you separate part-way into New Jersey?'" Hinkel said. "The quick answer to that is that the electrical system doesn't exactly reflect geopolitical boundaries."

Early on Aug. 14, PJM control-room operators took steps to gird for what was expected to be unusually high air-conditioner use amid hot and humid weather, Hinkel said. Generators in the region were ordered to raise voltage levels to 1 % to 2 % above normal. It was a precaution based on lessons learned from the summer of 1999, when a power shortage caused voltage levels to drop and nearly collapsed the system, he said.
Sometime between 3:30 p.m. and 4 p.m., power that had been flowing east into PJM from the Ohio grids of American Electric Power Co. and FirstEnergy suddenly reversed course, Hinkel said. Reasons for the shift were unclear and are still under investigation, he said. "It was not something you could relate to a scheduled change," he said.

The operators consulted by phone with their counterparts from the Midwest Independent Transmission System Operator, which monitors the grids in Michigan, Indiana and northern Ohio. They took no action, and the next sign of distress came as a series of power failures in the two minutes before 4:11 p.m. on the American Electric system and PJM's own system, he said.
In the control room in Norristown, engineers watched the darkness spread as blinking alarm lights on a transmission map the width of a tennis court. "All these lines suddenlylighted up," Hinkel said. "We can't see literally what's going on in New York, but we could see that our facilities going into New York were no longer in service."
Among the lines lost were connections to the Stolle Road and Watercure substations of Energy East's New York State Electric & Gas utility in western New York, he said. Also severed were connections to FirstEnergy's substations near Erie, Pennsylvania, he said.