Read More: New Scientist
In July 2012 India experienced the largest power outage in history. More than 620 million people were left without electricity after a transmission line in the northern part of the country failed, buckling under too much electrical load. Nearby power lines that took up the slack also failed, and lights across 22 Indian states went out. All power grids are at risk of this rare domino effect, called a cascading failure, and pinpointing which parts of the grid are most vulnerable could prevent future costly blackouts. Takashi Nishikawa at Northwestern University in Evanston, Illinois and colleagues modelled this risk in the North American power grid. Surprisingly, they found that only 10.8 per cent of all links in the US and southern Canada were at risk of failing in a cascade event. Their model incorporated data from the Federal Energy Regulatory Commission between 2008 to 2013, and accounted for factors like changing seasons and power demand levels. Nishikawa says more vulnerable links are located near densely populated cities, where there are a greater number of power lines that are connected to each other. Building redundancy “With almost 100,000 lines considered, this is the largest study of cascading failures I have seen so far,” says Stefan Kettemann at Jacobs University in Bremen, Germany. Kettemann says that this simulation goes beyond previous studies in that it incorporates how quickly these power lines heat up and fail. Power grids protect against failures by building redundant paths – if a line is damaged by wildfires or falling trees another can take over – but cascading failures take out these redundancies too. When the failed line’s power is rerouted to another line, that line can also become overloaded and fail. Unlike when Puerto Rico’s electrical grid went down because of damage from Hurricanes Irma and Maria, cascading failures happen because of what’s happening inside the grid. Initial failures that are close together are more likely to lead to larger cascades, Nishikawa says. Utility companies can now prioritise the upgrade and maintenance of those weak links with the highest frequency of past failures, he says. Identifying which lines are most vulnerable presents a cost-effective way of preventing future cascades and improving grid resilience.