The U.S. Advanced Research Projects Agency-Energy (ARPA-E) is funding research at Georgia Tech to come up with an alternative to sulfur hexafluoride gas (SF₆) used to protect circuit breakers from overloads and other faults.

The need for a new material stems from the negative impact of SF₆. While it “is a fantastic insulator,” according to Johan Enslin, a program director at ARPA-E, “it's very bad for the environment—probably the worst greenhouse gas you can think of.”

Sulfur hexafluoride has a global-warming potential nearly 25,000 times higher than carbon dioxide, according to IEEE Spectrum, a magazine published by the Institute of Electrical and Electronics Engineers. It’s currently used to insulate almost all high-voltage circuit breakers around the world, but the European Union and California are phasing it out, meaning there is a need to find another gas.

Current circuit breakers stop a current during a lightning strike or other emergencies using a mechanical interrupter in an enclosure containing SF₆, a nonconductive insulating gas. When a fault occurs, the device breaks the circuit by “mechanically creating a gap and an arc, and then blasting high-pressure gas through the gap. This halts the current by absorbing free electrons and quenching the arc as the dielectric strength of the gas is increased,” according to Spectrum.

Georgia Tech’s design uses supercritical carbon dioxide, a safer material, researchers say, to quench the arc. Made by putting CO₂ under very high heat and pressure, it transforms into something between a gas and liquid. Researchers believe it can quench an arc and avoid reignition of a new arc in faulty circuits by slowing electron flow.

While the use of supercritical CO₂ isn’t new, designing a circuit breaker around it is. Researchers had to build the breaker with components capable of withstanding the high pressure needed to sustain supercritical CO₂.

One component had to be specially created for this project. There were no bushings able to withstand 120 atmospheres of pressure, so Georgia Tech designed one, using mineral-filled epoxy resins, copper conductors, steel pipes and blank flanges.

Testing has begun on a synthetic circuit. If successful, this first-of-its-kind device will be put through real-world simulations at KEMA Laboratories in Chalfont, Pa. If those tests are successful, it could eventually replace conventional high-voltage breakers.

The ultimate goal is to limit heat-trapping air pollution and move to renewable energy, thereby reducing greenhouse gas emissions. Just 1% of SF₆ leaks result in roughly 9,000 tons of harmful fumes. Georgia Tech has also been working on improvements to the power lines so they can accommodate more renewable energy.