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Original photo: Emily Waltz []Researchers this month will begin testing a high-voltage circuit breaker that can quench an arc and clear a fault with supercritical carbon dioxide fluid. The first-of-its-kind device could replace conventional high-voltage breakers, which use the potent greenhouse gas sulfur hexafluoride, or SF[6.] Such equipment is scattered widely throughout power grids as a way to stop the flow of electrical current in an emergency. "SF[6] is a fantastic insulator, but it's very bad for the environment--probably the worst greenhouse gas you can think of," says Johan Enslin, a program director at U.S. Advanced Research Projects Agency-Energy (ARPA-E), which funded the research. The greenhouse warming potential of SF[6] is nearly 25,000 times as high as that of carbon dioxide, he notes. If successful, the invention, developed by researchers at the Georgia Institute of Technology, could have a big impact on greenhouse gas emissions. Hundreds of thousands of circuit breakers dot power grids globally, and nearly all of the high-voltage ones are insulated with SF[6]. A high-voltage circuit breaker interrupter, like this one made by GE Vernova, stops current 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.GE Vernova On top of that, SF[6] by-products are toxic to humans. After the gas quenches an arc, it can decompose into substances that can irritate the respiratory system. People who work on SF[6]-insulated equipment have to wear full respirators and protective clothing. The European Union and California are phasing out the use of SF[6] and other fluorinated gases (F-gases) in electrical equipment, and several other regulators are following suit. In response, researchers globally are racing to develop alternatives. Over the past five years, ARPA-E has funded 15 different early-stage circuit-breaker projects. And GE Vernova has developed products for the European market that use a gas mixture that includes an F-gas, but at a fraction of the concentration of conventional SF[6] breakers. Reinventing Circuit Breakers With Supercritical CO[2] The job of a grid-scale circuit breaker is to interrupt the flow of electrical current when something goes wrong, such as a fault caused by a lightning strike. These devices are placed throughout substations, power-generation plants, transmission and distribution networks, and industrial facilities where equipment operates in tens to hundreds of kilovolts. Unlike home circuit breakers, which can isolate a fault with a small air gap, grid-scale breakers need something more substantial. Most high-voltage breakers rely on a mechanical interrupter housed in an enclosure containing SF[6], which is a nonconductive insulating gas. When a fault occurs, the device breaks the circuit by mechanically creating a gap and an arc, and then blasts the high-pressure gas through the gap, absorbing free electrons and quenching the arc as the dielectric strength of the gas is increased. In Georgia Tech's design, supercritical carbon dioxide quenches the arc. The fluid is created by putting CO[2] under very high pressure and temperature, turning it into a substance that's somewhere between a gas and a liquid. Because supercritical CO[2] is quite dense, it can quench an arc and avoid reignition of a new arc by reducing the momentum of electrons--or at least that's the theory. Led by Lukas Graber, head of Georgia Tech's plasma and dielectrics lab, the research group will run its 72-kilovolt prototype AC breaker through a synthetic test circuit at the University of Wisconsin-Milwaukee beginning in late April. They group is also building a 245-kV version. The use of supercritical CO[2] isn't new, but designing a circuit breaker around it is. The challenge was to build the breaker with components that can withstand the high pressure needed to sustain supercritical CO[2], says Graber. The team turned to the petroleum industry to find the parts and found all but one: the bushing. This crucial component serves as a feedthrough to carry current through equipment enclosures. But a bushing that can withstand 120 atmospheres of pressure didn't exist. So Georgia Tech made its own using mineral-filled epoxy resins, copper conductors, steel pipes, and blank flanges. "They had to go back to the fundamentals of the bushing design to make the whole breaker work," says Enslin. "That's where they are making the biggest contribution, in my eyes." The compact design of Georgia Tech's breaker will also allow it to fit in tighter spaces without sacrificing power density, he says. Replacing a substation's existing circuit breakers with this design will require some adjustments, including the addition of a heat pump in the vicinity for thermal management of the breaker. If the tests on the synthetic circuit go well, Graber plans to run the breaker through a battery of real-world simulations at KEMA Laboratories' Chalfont, Penn. location--a gold-standard certification facility. A high voltage circuit breaker against a solid color background.The Georgia Tech team built its circuit breaker with parts that can withstand the very high pressures of supercritical CO2.Alfonso Jose Cruz GE Vernova Markets SF6-Alternative Circuit Breaker If Georgia Tech's circuit breaker makes it to the market, it will have to compete with products from GE Vernova, which had a 20-year head start on developing SF[6]-free circuit breakers. In 2018, the company installed its first SF[6]-free gas-insulated substation in Europe, which included a 145 kV-class AC circuit breaker that's insulated with a gas mixture it calls g^3. It's composed of CO[2], oxygen and a small amount of C[4]F[7]N, or heptafluoroisobutyronitrile. This fluorinated greenhouse gas isn't good for the environment either. But it makes up less than 5 percent of the gas mixture, so it lowers the greenhouse warming potential by up to 99 percent compared with SF[6]. That makes the warming potential still far greater than CO[2] and methane, but it's a start. "One of the reasons we're using this technology is because we can make an SF[6]-free circuit breaker that will actually bolt onto the exact foundation of our equivalent SF[6] breaker," says Todd Irwin, a senior product specialist in high-voltage circuit breakers at GE Vernova. It's a drop-in replacement that will "slide right into a substation," he says. Workers must still wear full protective gear when they maintain or fix the machine as they do for SF[6] equipment, Irwin says. The company also makes a particular type of breaker called a live-tank circuit breakerwithout the fluorinated component, he says. All of these approaches, including Georgia Tech's supercritical CO [2,] depend on mechanical action to open and close the circuit. This takes up precious time in the event of a fault. That's inspired many researchers to turn to semiconductors, which can do the switching a lot faster, and don't need a gas to turn off the current. "With mechanical, it can take up to four or five cycles to clear the fault and that's so much energy that you have to absorb," says Enslin at ARPA-E. A semiconductor can potentially do it in a millisecond or less, he says. But commercial development of these solid-state circuit breakers is still in the early stages and is focused on medium voltages. "It will take some time to get them to the required high voltages," Enslin says. The work may be niche, but the impact could be high. About 1 percent of SF[6] leaks from electrical equipment. In 2018, that translated to 8,200 tonnes of SF[6] emitted globally, accounting for about 1 percent of the global-warming value that year. From Your Site Articles * Atom Power Is Launching the Era of Digital Circuit Breakers > * Inside the Lab That Pushes Supergrid Circuit Breakers to the Limit > Related Articles Around the Web * Sulfur hexafluoride - Wikipedia > * Sulfur Hexafluoride (SF6) Basics | US EPA > circuit breakersclimate techsupercritical carbon dioxidesolid state circuit breakersgrid {"imageShortcodeIds":[]} Emily Waltz Emily Waltz is a features editor at Spectrum covering power and energy. Prior to joining the staff in January 2024, Emily spent 18 years as a freelance journalist covering biotechnology, primarily for the Nature research journals and Spectrum. Her work has also appeared in Scientific American, Discover, Outside, and the New York Times. Emily has a master's degree from Columbia University Graduate School of Journalism and an undergraduate degree from Vanderbilt University. With every word she writes, Emily strives to say something true and useful. She posts on Twitter/X @EmWaltz and her portfolio can be found on her website. The Conversation (0) The silhouette of a man standing outside a pub illuminated by a camping lamp during a blackout. The surrounding area is nearly pitch black. EnergyNews Rules, Not Renewables, Might Explain the Iberian Blackout 2h 4 min read Illustration of a gloved hand holding a computer chip against a gradient background. CareersSemiconductorsInterview Why the Semiconductor Industry Can't Abandon Women 7h 6 min read Schematic collage of an alumni nuclear thermal propulsion system surrounded by a dark starry sky. 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