Two groups of researchers have independently brought forward evidence of intrinsic weaknesses in the North American power grid. Their analyses both conclude that massive power blackouts such as the one that took out New York last summer are likely to happen again.
Last week, John Kappenman, a US Government advisor from the California-based company Metatech Corporation, told the annual meeting of the American Meteorological Society in Seattle, Washington, that geomagnetic storms could cause much larger blackouts. And, he warned, the way the grid is growing only makes it more vulnerable. "The threat is greater than anyone had previously thought," says Kappenman.
The Sun ejects streams of charged particles that can warp the Earth's magnetic field, producing dazzling atmospheric effects such as the aurora borealis. The changing magnetic field also induces a direct current in transformers. This causes huge electrical surges, because the grid is only meant to take alternating current. "It's very difficult to design a transformer that can cope with this," says Kappenman.
The effect on power grids can be devastating. In 1989, the Quebec power grid was shut down within 90 seconds of one major geomagnetic storm.
As the grid grows, and more inter-connecting wires are added to the system, it actually becomes more vulnerable to such storms, says Kappenman. "It lowers the total electrical resistance of the system, effectively making a bigger antenna for picking up induced current," he says. Over the last 50 years, there has been a tenfold increase in the lengths of power lines in the US. "The power companies have unwittingly built risks into the grid, and the risk is spiralling out of control," he says.
Mapping the grid
In a separate study, Réka Albert of Pennsylvania State University and her co-workers constructed a model of the US network, in part to work out why the system failed in last summer's blackout.
The exact cause of the breakdown hasn't been pinned down, but the outages seem to have propagated over the grid in a cascade. Power lines are automatically shut down if they reach too high a voltage, and generating stations switch off if they cannot transmit their power. As power stations and transmission substations were knocked out, power was shifted to lines further down the network, causing them to overload too.
To model that process, the team constructed a map of the US containing over 14,000 generating, transmission and distribution substations, and 19,000 connecting power lines1. They conclude that the US power grid is a so-called 'exponential network', in which most of the network functions without giant hubs that connect large sections of the network together. However, the few well-connected hubs that do exist are crucial to the power distribution. If those transmission substations that bear the highest power loads are the first to break down, failure of just 4 % of them leads to a break-up of around 60 % of the network, they found.
The situation was even worse when the researchers took into account how the failure of some substations shunts power loads onto the others, causing them to overload. In that case, the loss of just 2 % of the highest-load transmission substations cut off 60 % of the network.
Albert concludes that one way to make the grid more resilient would be to add more small power-generating substations to ease the job of transmission. The cheapest option, she adds, would be to add more connections between substations, so that there are more alternative routes when some lines fail.
But Kappenman points out that this would make the grid's vulnerability to space weather even worse. In order to protect the grid, he says, resistors would have to be installed at strategic points, which could reduce the induced currents by 60-70%. That would cost a few million dollars, says Kappenman.
"Vulnerability of the electric power grid is inherent to its organization and therefore cannot be easily addressed without significant investment," writes Albert. Experts have already acknowledged that upgrading the US grid to prevent future blackouts could cost $100 billion. All the same, says Albert, "it's got to be done."
1. Albert, R., Albert, I.. & Nakarado, G. L. Structural vulnerability of the North American power grid. Preprint, xxx.lanl.gov/abs/cond-mat/0401084 (2004). |Article|
© Nature News Service / Macmillan Magazines Ltd 2004