Detroit Edison Co. (DE) has received approval from the Michigan Public Service Commission for
10-year sole-supplier contracts for electric power and related services with Chrysler, Ford,...
around for a long time, since before World War II."
Loehr says Hydro-Quebec has two major DC interconnections with the United States-one with New York and one with New England. Loehr says Hydro-Quebec uses DC for technical reasons. "It could not interconnect with the Eastern Interconnection or with other Canadian provinces, but they were able to overcome that problem by using DC ties," he explains. "ERCOT also was a separate interconnection and found that to tie into the Eastern Interconnection to buy and sell power was much more feasible by using DC," he notes.
Loehr claims that use of DC would have avoided the August blackout. "The advantage of DC is that it is not subject to Kirkoff's laws," Loehr points out. "With an AC system, if something happens at one end of an AC system, then that is broadcast to the other side," he explains. "So if the lines trip in Ohio, we feel it in New York, but if you have DC, that is not the case."
"Let's say you have a situation on Aug. 15 where New England, New York, and Ontario are operating as a separate interconnection, with DC ties to the rest of the world," offers Loehr. The problems in Ohio would not have caused any problems in those three areas. "The only effect you could have on a neighboring system is the neighboring system would have maybe the loss of any power that had been flowing on the tie," but Loehr adds "you would plan for that anyway, even if it were an AC system."
Loehr also believes the proposed DC system would cost less to upgrade the North American grid than numbers being thrown around post-blackout. "I did estimates of the cost for DC, and they all seemed to average out to about $100,000 per mega-watt at each end of the line to converter stations," he says. He did the math and came up with estimates of between $7 billion and $8 billion. Those costs would match the capabilities of the present grid, which might need to be enhanced in some places and lessened in places. -L.A.B.
Toward Bigger Blackouts?
The 2003 blackout was larger than the 1965 blackout geographically, and George Loehr believes any future blackouts will be even bigger.
He makes that conclusion based on the existence of many more high-voltage transmission lines today. The resulting effect is that impedances between one point in the system and another point decline. Loehr explains that if you take Point A and Point B with one transmission line through it, and now have impedance X, and then build another identical line, impedance is now X divided by two. Then build two more, it is X divided by four. That leaves one-quarter the amount of impedance between those two points than existed with just one line. Basically, the grid is infinitely more complicated, and when more transmission is built, impedance is lowered across the system. If something happens somewhere in the interconnection, it is going to be felt more strongly by places far