Scientists pinpoint ‘weak spots’ that cause mass blackouts

Source: Christa Marshall, E&E News reporter • Posted: Monday, November 20, 2017

Scientists have developed an unprecedented map of the U.S. grid’s weak spots that could help prevent life-threatening and costly mass blackouts.

To date, it has been difficult to predict and analyze large grid failures because of a lack of data and the complexity of factors — from extreme weather to cyclical electricity demand — that can affect outages.

Northwestern University researchers say they have now filled a critical knowledge gap by identifying grid patches especially vulnerable to “cascading failures.”

In a study published this week in Science, they reported that a relatively small group of transmission lines — or about 10.8 percent of the U.S.-Canada grid — are disproportionately responsible for primary failures of lines that can multiply throughout a network.

With the new map, utilities and policymakers may be able to prioritize upgrades and increase monitoring in weak spots to prevent future problems, they say.

“Previous studies on cascades were done on small-scale systems or used models that did not account for the laws of physics,” said Takashi Nishikawa, an associate professor at Northwestern University who was involved in the research. “What is different in our study is that we look at the entire contiguous U.S.”

In total, the team examined more than 100,000 power lines. The vulnerable arteries are scattered throughout the country but often are located near populated regions.

That’s partly because there are so many lines in those areas but also because there can be many lines in dense areas tied to the same substation, Nishikawa said.

“Lines linked to such highly connected nodes tend to be more vulnerable,” he said.

The researchers analyzed data from the Federal Energy Regulatory Commission on the U.S.-Canada grid system from 2008 to 2013 to develop a model of the connectedness of networks across the continent.

Numerous simulations of the grid under a range of conditions, such as at different times of day and in different seasons, allowed detailed understanding of power line behavior.

Under some conditions, 1 percent of the entire network seemed vulnerable in the simulations. In others, it was a different percentage. But in total, the parts of the network prone to a “primary failure” that can cause a ripple effect capped at about 10.8 percent.

The study did not consider all factors that might affect power lines, such as their age, because data was not available. But Nishikawa said more simulations likely wouldn’t increase the vulnerable percentage much.

The team released a video of the research. A primary failure can occur on a power line for a variety of reasons, such as a fallen tree or storm.

Usually those primary failures stay localized, but they can cascade when other lines have to pick up the slack and get overloaded, said Nishikawa.

Not all blackouts are caused by cascading failures, but when there is such an event, it typically causes a shutdown of power to customers.

The result can be devastating. In 2003, a blackout in the Northeast contributed to 11 deaths and cost more than $6 billion, according to some estimates.

Nishikawa said one way to prevent some events would be to increase capacity within individual power lines so they are less likely to overload and cause a domino effect. Adding additional lines in some areas also could be helpful, he said.

In a perspective article in Science, University of California, Davis, computer science professor Raissa D’Souza said the study establishes important insights for the power grid that should have wider-reaching implications.

Understanding cascading failures “will be a key to eventually designing control interventions for avoidance and rapid recovery,” D’Souza said.