Shaky Dominoes: Hardening Power Grids Against Cascading Failure

Shaky Dominoes: Hardening Power Grids Against Cascading Failure

August 26th, 2013 | by Charles Q. Choi

Ten years ago, a giant power blackout hit the northeast United States and Canada. At the time, it was the second most widespread electricity outage in history. But n researchers have found that an even bigger event is more likely than many would like to think. A recent study revealed that the power grids that span continents are even more vulnerable to catastrophic failure than previously believed.

Many kinds of networks can be linked together to form complex systems like the interlinked network of websites we call the World Wide Web. Recent studies regarding these kinds of systems, which are called interdependent, found that once a certain fraction of the nodes comprising them fail — say, 20 or 30 percent — the interdependent network would not just gradually fail, but abruptly and totally collapse.

"When you have a system where some networks depend on others, it can collapse by cascading failure. Since one network depends on others, once nodes in one network fail, you have failure in another, and then another, and so on," says Shlomo Havlin, a physicist at Bar Ilan University in Ramat Gan, Israel. 

Factoring in the real world

Previous research assumed where the nodes making up these interdependent networks were located in space was not important. In contrast, the distances between these nodes in many real-world systems are critical. In power grids, for example, the length of power lines influences how electricity gets transmitted.

The researchers unexpectedly found that when it comes to interdependent networks where space does matter, abrupt collapse of those networks can occur if they depend on each other to any degree.

"They are extremely vulnerable to failure," Havlin says. "It is frightening. We are living in a very risky world."

The mathematical framework to analyze interdependent networks on a fundamental level is relatively new, “only really existing since about 2010,” says researcher Amir Bashan, another Bar Ilan University physicist. “People first studied interdependent networks that were not embedded in space. This is the first time that interdependent networks embedded in space have been studied in depth, and we were very surprised about what we found.”

When it comes to interdependent networks where space does not matter, every node can be connected to every other node. As such, if you have a failure in one node, activity can reroute around those nodes relatively easily. However, when it comes to systems where space does matter, “you don’t have these shortcuts, and that makes them very vulnerable,” Havlin says.

The researchers tested the stability of two real-world interdependent networks with complex spatial features— the western United States and European power grids — and found they were no better than their lab models.

Depending on the nature of the system, “if any fraction of nodes fail in power grids — 10 percent, 1 percent, 0.1 percent — you can have an abrupt collapse,” Havlin says. “This could happen due to overload. An overload in one place can lead to overload in another, and then both of those can lead to overload in yet more places, and so on.”

Better data means hardened systems

The scientists are now investigating ways to make these networks more robust against catastrophic failure. “If you add a few long-range links between some nodes to serve as shortcuts, the system should behave very differently,” Bashan says.

Discovering more about the behavior of spatially embedded interdependent networks could have applications far beyond power grids. “If we can generate physical systems that behave more abruptly, we can make high-performance instruments and sensors that are much more accurate or sensitive to different changes,” Havlin says.

Conversely, research in this area could lead to new ways to attack systems. “If you can identify and know the structure of a system, you could identify nodes that are really critical for abrupt collapse of that system,” Havlin says. “It could take just one node.”

The scientists detailed their findings online Aug. 25 in the journal Nature Physics.

Top Image: Powerlines via Shutterstock.

Charles Q. Choi
 has written for Scientific American, The New York Times, Wired, Science and Nature, among others. In his spare time, he has traveled to all seven continents, including scaling the side of an iceberg in Antarctica, investigating mummies from Siberia, snorkeling in the Galapagos, climbing Mt. Kilimanjaro, camping in the Outback, avoiding thieves near Shaolin Temple and hunting for mammoth DNA in Yukon.

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