Oak Ridge National Laboratory (ORNL) says it has cleared a stubborn hurdle in power distribution: how to shut off medium-voltage direct current quickly and affordably. The lab’s team has built a semiconductor-based circuit breaker that interrupts a 1,400-volt DC fault in under 50 microseconds and has demonstrated a stacked design that handles up to 1,800 volts.
The lab’s development arrives at a key moment: AI-era data centers are chasing more megawatts than local grids can easily supply. DC distribution, protected by microsecond-class breakers, can make the electrons already available go further and safer. The promise is a protective device fast enough for DC systems, and cheap enough to deploy at scale.
In a throwback to earlier decades, the ORNL work focused on the basic science of electricity. Circuit breakers are a needed safety feature to prevent electrical overload. Legacy circuit breakers are well equipped to handle alternating current, AC, which is the electricity that commonly flows through most power grids. But direct current, DC, moves only in one direction and is much faster and more efficient—but it proves more challenging for circuit breakers.
“The lack of medium-voltage circuit breakers for direct current has been an obstacle to flexibility in delivering electricity,” said Prasad Kandula, who leads ORNL’s Grid Systems Hardware group.
The solution ORNL found doesn’t use next-gen silicon. The prototype relies on thyristors, a mature component first used in the 1950s. Thyristors are robust and inexpensive, but they don’t turn off on command. ORNL created an external circuit that forcibly drives current to zero, allowing the device to clear faults in tens of microseconds—far faster than the tens of milliseconds typical of mechanical breakers. That speed slashes energy during a fault, reducing fire risk and collateral damage.
Data centers are inherently DC. Each conversion step to interface with an AC-centric grid wastes energy and adds cost. Direct-current feeders can simplify those paths and handle bidirectional electricity flows. But DC electrical problems are unforgiving: mechanical devices struggle to quench arcs before heat builds. The ORNL circuit breaker could potentially solve this problem.
The ORNL development isn’t ready for commercial use. Medium-voltage distribution in data centers can involve thousands of amps. ORNL’s work focused on voltage and speed, while important issues like sustained current, thermal performance, and repeated fault endurance still need to be proven. Reliability certification and coordination with upstream/downstream protection will be essential before real world grids can adopt the design.
If those hurdles are cleared, the potential is significant. Faster, non-arcing interruption reduces wildfire risk and equipment damage, and could play a key role in supporting today’s massive data center buildout.
Kandula’s team positions the breaker as one building block in a broader push for modular, stackable power hardware that can be mixed and matched for data centers and other industrial uses. As Oak Ridge moves from prototypes toward higher voltage and current, the question shifts from how fast DC can be switched to whether DC can be switched affordably and at scale. ORNL’s answer uses old silicon with new control, a pragmatic approach that could provide a much-needed boost to today’s stressed electrical grids.
