DOE’s Oak Ridge Lab Advances Semiconductor-Based Breakers for Future DC Power Systems

Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) are utilizing 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, which can help reduce future electricity costs and expand capacity in an overburdened U.S. grid.

Circuit breakers 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. Traditional breakers work well with alternating current, or AC. AC is easy to interrupt because it changes direction 60 times per second, while direct current, or DC, flows in only one direction.

ORNL researchers are designing and increasing the capacity of a new type of semiconductor-based circuit breaker, which can operate faster as compared to mechanical switches. This will help 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 does not have to be converted between DC-based power electronics and an AC-based grid.

A DC-only system wastes less power, increasing power grid capacity and reducing energy costs, while better supporting the multi-directional power flows of the modern grid.

Medium-voltage circuit breakers are crucial for DC power distribution. DC systems rely on fast-acting power electronics, which require equally fast protection.

Semiconductors offer both speed and greater safety for DC systems. Traditional mechanical breakers rely on a physical gap that is less effective in stopping DC, which is capable of sparking across a gap in an arc of explosive energy. To avoid the possibility of arcing, the current can instead be routed away through a semiconductor-based device, reducing safety risks and wildfire risks.

Currently, semiconductor breakers are expensive to either compete economically with mechanical breakers for AC, or to facilitate expanded use of DC grids. No type of commercial breaker can handle DC above 2,000 volts, and most are not able to achieve half of the capacity

Prasad Kandula, lead researcher and his team set out to find a cost-effective solution to fill this performance gap. They focused on an older, industry-accepted semiconductor called a thyristor, which is affordable to make semiconductor-based switches competitive for the first time.

Thyristors cannot be directly switched off, so the team also had to design an external circuit to forcibly reduce the current. In ORNL’s Grid Research Innovation and Development Center, or GRID-C, engineers built and tested a circuit breaker prototype to interrupt a current at 1,400 volts in less than 50 microseconds, which is four to six times faster than had been demonstrated with thyristors previously.

Researchers connected the breakers in a series, meaning one after another along the same electrical path, to prove the technology could be scaled up to handle higher voltages. The approach came with several technical challenges like:

• The voltage must be shared evenly across all breakers, to prevent any single device from becoming overloaded and failing.
• Creating a series of breakers should not delay the system’s rapid reaction time.

ORNL researchers designed solutions and tested them in a series of breakers operating up to an 1,800-volt testing capacity. They are working on adding to the series for eventually scaling up to 10,000 volts, anticipating the larger energy demands of future DC grids.

The project is part of an ORNL initiative to develop a menu of stackable medium-voltage building blocks for expanding new power applications in U.S. transportation, manufacturing and data centers. Other researchers who contributed to the project, which is supported by the DOE Office of Electricity, include Marcio Kimpara and Elvey Andrade.

UT-Battelle manages ORNL for the Department of Energy’s Office of Science, the supporter of basic research in the physical sciences in the United States.