Researchers at the Department of Energy’s Oak Ridge National Laboratory are breaking technical barriers with faster circuit breakers to enable and protect the modern electric grid. The ORNL team developed medium-voltage circuit breakers capable of handling increasing levels of direct current at a lower cost, an advance that can help reduce future electricity costs and expand capacity in an overburdened U.S. grid.
“The lack of medium-voltage circuit breakers for direct current has been an obstacle to flexibility in delivering electricity,” said Prasad Kandula, lead researcher. “Developing this technology helps keep the grid working safely and reliably while keeping more energy available to support our growing population and economy.”
Circuit breakers are a longtime safety feature in the grid that automatically interrupt the flow of electrical current if it exceeds its intended magnitude or a fault in the system allows the current to follow an unintended path. For example, if a power line touches the ground, a mechanical circuit breaker or fuse can cut the flow of current, reducing the risk of a fire or power outage. Traditional breakers work well with alternating current, or AC, which is the kind of electricity that flows through most of the power grid and into buildings. AC is easy to interrupt because it changes direction 60 times per second. But direct current, or DC, flows in only one direction.
“Once you go to DC, that ‘zero current’ moment is gone — and without it, a mechanical switch isn’t fast enough to stop a fault before heat builds up and a fire starts,” said Kandula, who leads ORNL’s Grid Systems Hardware group.
To tackle this problem, ORNL researchers are designing and scaling up the capacity of a new type of semiconductor-based circuit breaker, which can operate a hundred times faster than mechanical switches. This enables wider use of DC in the electric grid as it becomes more attractive to energy system designers for its efficiency, flexibility and compatibility with modern energy sources and loads.
DC systems can provide more affordable electricity for energy-intensive economic development projects such as AI data centers. This is because DC flows with less resistance through power lines, losing less energy in transit. Additional losses are prevented when current doesn’t have to be converted between DC-based power electronics and an AC-based grid.