TORONTO — A massive electrical transmission system known as the Lake Erie Loop — the focus of the investigation into the massive blackout — has been a unique and challenging part of the U.S.-Canadian power system for many years.
Ringing the fourth largest of the Great Lakes, the loop circles from Detroit through Ohio, Pennsylvania, the Niagara Falls area of New York and southern Ontario before re-entering Michigan.
Power can flow clockwise or counterclockwise around the roughly 1,000-mile loop, depending on weather conditions and the intricacies of supply and demand. Responsibility for its oversight and operations is shared by an array of utility companies, industry councils and government agencies from Canada and the U.S. states that get power from it.
"The loop is fairly unique — I don't know of any other place where you have a lake in the middle of it," said Ron May, a senior vice president of Michigan-based DTE Energy. "It does take an effort for the guys who operate it."
The North American Energy Reliability Council, or NERC, which is charged with assessing the dependability of the electric grid system, has pointed to a section of the loop in Ohio as the likely point of origin for Thursday's blackout.
"That's the center of the focus," NERC chief Michehl Gent said. "This has been a problem for years and there have been all sorts of plans to make it more reliable."
The root cause of the problem, experts say, is that demand for power from the loop has grown, while relatively few new power plants have been built to feed the demand, primarily because of environmental concerns.
"If the system is very heavily loaded, the margin for stability is narrow," said Roger King, an electrical engineering professor at the University of Toledo. "The solution is going to be to build a lot more power plants, but that's very costly."
The Lake Erie Loop is among the largest of several power-sharing arrangements between Canada and the United States — provinces from New Brunswick in the east to British Columbia in the west have interconnected with U.S. utilities for decades.
In most cases, these arrangements were designed so that Canada, with its rich hydroelectric resources, could export surplus electricity to U.S. buyers. But one of the complications for the Lake Erie Loop has been surging demand for electricity in Ontario, Canada's most populous province — to the extent that the loop is often used, especially in cold winter months, to import American power into Ontario.
In addition, the loop has been used by U.S. power companies in the Midwest to send power through the Ontario part of the line to purchasers in eastern states.
Don Benjamin, NERC's vice president, said the loop can experience major changes of power back and forth.
"It's very difficult to build devices to control power," he said, although he noted that authorities in Ontario and Michigan were considering investment in expensive new transformers that can help force power make a desired change of direction.
Amid the post-blackout fingerpointing, people on both sides of the U.S.-Canada border have asked why their local utilities should be vulnerable to problems that might occur across the border. Officials reply that the interdependence has plusses as well as potential complications.
"There is something to be said for connecting the grid to our largest trading partner," said Ontario Premier Ernie Eves. "It has benefits for both sides."
The loop design, enabling power to flow in either of two directions, can be an asset most of the time in ensuring reliable, market-priced supplies, said Herman Hill, a professor of electrical engineering at Ohio University.
"But the configuration changes every time something is switched in," he said. "That makes it difficult to analyze, and also means you do have this possibility of cascading outages."
DTE Energy's May noted there had been several ownership changes in recent years among utilities that use the loop.
"There are a variety of entities that have some oversight," he said. "It's a little complex, but the bottom line is that it's worked well."
However, the complications of the Lake Erie Loop have been cited on various occasions in recent years, for example in a 1998 NERC report that identified the Michigan-Ontario interface as an area where a power shortfall could occur.
Last year, a company called Lake Erie Link Ltd. proposed bypassing the loop by building an underwater power line to link Ontario power plants with locations on the south shore of the lake in Pennsylvania or Ohio. As part of its proposal, which is now on hold, the company noted that operators of the Lake Erie Loop were facing costly investments in order to maintain control over unintended power flows through the loop.