At least 10 million people experienced a blackout in Northeastern Brazil this morning when an electric substation knocked out transmission lines and temporarily shut down generation capacity.

Problems at the Luiz Gonzaga substation in the state of Pernambuco likely caused the automatic shutdown in part of the national transmission grid. Minister Edison Lobao said in a televised press conference that one of the circuits failed at the substation, and when workers tried to reconnect the circuit a problem occurred that shut down both of the circuits from the substation. That caused an automatic shutdown of part of the region's generators to avoid overloading the system. The northeast also was isolated from the rest of the national grid to avoid problems elsewhereleading to a drop in energy supply to the northeast region. Supply dropped to 800 MW, from the normal supply of 8800 MW, the Wall Street Journal reported.

Associated Press reported that the power failures began in the early morning and quickly spread across seven states in the vast region. The blackouts hit four cities scheduled to host World Cup football matches in 2014, but Lobao said officials were confident that energy supplies would not be a problem during the events.

Electricity was restored to the region within about five hours, Lobao said.

Brazil experienced another widespread outage a couple of years ago, this time in the southern half. In November 2009, a power failure started with the Itaipu dam, the world's second biggest hydroelectric producer, which supplies 20 percent of Brazil's electricity. Brazilian authorities blamed storms that took down power lines and towers, causing a domino effect that rippled across the region.

This time, Lobao said Brazil's grid was robust and modern, and that such failures can happen in any nation. "There are flaws," he said of Brazil's energy grid, "but there are flaws in systems all over the world."

According to the AP report, energy expert Jose Jardini, a professor of electrical engineering at the University of Sao Paulo, said the failure was likely an "abnormality, an accident" and that it didn't seem to point to more severe problems, such as supply not meeting energy demand, since the blackout happened in the early morning hours when demand is low.