FEW technological failures have been as widely predicted as the power cut to 50 million people in the north-eastern US and Ontario last week. Experts have repeatedly warned of problems with the ageing North American power grid. Its capacity has expanded little while the amount of power it is being asked to carry has soared, leaving safety margins razor-thin.
Alarm bells sounded in government last year when the National Transmission Grid Study, commissioned by the US Department of Energy, warned that North America鈥檚 limited grid capacity increased the risk of blackouts. The main reason is that the transmission system is not keeping up with the needs of deregulated power generation and delivery markets, says Brendan Kirby of the Oak Ridge National Laboratory in Tennessee. Investment in the US grid alone has dropped from about $5 billion a year in 1975 to $2 billion today.
The answer, says the industry-backed Electric Power Research Institute, is to spend between $50 to $100 billion on the grid. But no one expects to see a difference in the short term. On top of the expense, people do not want new high-voltage lines in their backyards, fearing property blight or alleged health problems. That means approval of a new line鈥檚 path can take a decade or more.
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The underlying problem is that the North American grid was designed decades ago merely as a back-up that would allow local suppliers to tap emergency power from neighbouring utilities. But a decade of regulatory changes has split power generation from transmission and distribution, so suppliers can now choose to buy electricity from power stations far away. This has led to heavy long-distance transmission on a grid that was not designed for it.
To regulate loads on the grid, transmission contracts must be approved by the North American Electric Reliability Council (NERC), a body created in the aftermath of a massive blackout in 1965. Michehl Gent, NERC鈥檚 president, said last week鈥檚 failure occurred because the rules were inadequate 鈥� or someone cheated.
Current flow through the grid depends on the power-draining loads attached. Technicians monitor this flow, switching power stations and transmission lines in or out to prevent damage to equipment and ensuring that demand does not exceed supply. These measures usually prevent failures affecting too many people, but on 14 August an unexplained failure on a 345-kilovolt line near Cleveland, Ohio, triggered a cascade of failures.
Current from the failed line automatically diverted to others, causing one to overheat and divert power in turn to other lines, one of which overloaded as well. Owner of the lines, FirstEnergy of Akron, Ohio, does not yet know why its monitoring system failed to alert operators. Eventually the cascade of lost lines and closed power stations caused strong swings in power transmission to Canada and the eastern US, triggering a rapid series of generator and grid shutdowns in Michigan, Ohio, Ontario and New York.
Last week鈥檚 failure is still being investigated, but it is clear that the fundamental problem is that the grid is operating closer and closer to system limits, says Mariesa Crow, an electrical engineer at the University of Missouri-Rolla. More capacity is needed, she says.
Any large power system is vulnerable to such failures, says Daniel Kirschen, a power specialist at the University of Manchester Institute of Science and Technology in the UK. But national grids in Europe are less vulnerable than in North America, because they tend to carry lighter loads over less distance, he says.
New technology offers other options. Cables can be added to existing routes but more pylons would be needed. High-temperature superconducting cables have potentially huge capacity, but a trial at a Detroit Edison power plant had to be abandoned last year because cryogenic coolant leaked from cable shrouds. A more promising technology, under test, will allow power companies to remotely switch off some heavy loads for short intervals during peak demand, says Kirby.