UWM tests the world’s first ‘supercritical CO₂’ circuit breaker – College of Engineering & Applied Science

Jun 11, 2025

UWM has taken a pioneering role in advancing the future of the U.S. electrical grid by hosting the world’s first testing facility dedicated to high-voltage circuit breakers that are more cost-effective and environmentally friendly than current technology.

Doctoral student Sadeed Hossain, electrical engineering, has been instrumental in this effort, helping to build and operate the test facility, called a “synthetic test circuit.” It is designed for evaluating next-generation circuit breakers in both high-current and high-voltage environments.

Traditional circuit breakers at substations rely on sulfur hexafluoride (SF₆) as an insulating medium needed to interrupt the flow of electrical current and protect infrastructure when something on the grid goes wrong.

However, SF₆ is an expensive and potent greenhouse gas that has toxic byproducts. As the grid ages, leakage has become a problem because, once in the atmosphere, SF6 lingers for literally thousands of years.

Georgia Institute of Technology developed a different kind of circuit breaker that uses supercritical CO₂, as a viable replacement for SF₆, created by putting CO2 under very high pressures and moderate temperature, supercritical CO₂ is a substance that’s somewhere between a gas and a liquid.

Lukas Graber, associate professor of electrical and computer engineering at Georgia Institute of Technology, collaborated with former UWM faculty member Chanyeop Park, to bring the testing part of the grant to UWM. Hossain has kept the project on schedule, culminating in the completion of tests in November.

The new circuit breaker is designed to interrupt extremely high fault currents – up to 20,000 amperes (peak) – and is rated for operation at 72,000 volts, roughly the levels used to power large-scale facilities, such as major league baseball stadiums.

“Our industrial lab is the only university-based synthetic test circuit in U.S.,” Hossain said. “We built it to accommodate testing of supercritical CO2, but it can be used to test any kind of high-voltage circuit breakers.”

“Now that the basic science has been completed through this partnership, Midwest companies can take advantage of this facility and work with us to design and test new high-voltage circuit breakers,” said Andrew Graettinger, associate dean for research in UWM’s College of Engineering & Applied Science. “It’s a great example of academic collaboration opening doors to support the economy.”

As an undergraduate research assistant, recent graduate Samuel Catania (’25 BS, Electrical Engineering) developed a remote “command center” that allows high-voltage testing to be conducted safely from a separate control area outside the testing zone. To enhance electrical isolation and safety, the system is connected using fiber optic cables instead of traditional copper wiring.

The work behind this new circuit breaker and testbed was funded by the Department of Energy’s Advanced Research Projects Agency-Energy.