First Supercritical CO2 Circuit Breaker Debuts as Grid-Scale SF6 Alternative

Figure 1: Visual representation of the BeyondTrust vulnerability chain

Researchers at Georgia Institute of Technology have demonstrated a 72-kilovolt circuit breaker that uses supercritical carbon dioxide as its insulating medium, offering a potential replacement for sulfur hexafluoride in high-voltage electrical equipment. The prototype, developed under funding from the U.S. Department of Energy's ARPA-E CIRCUITS program, addresses growing regulatory pressure to eliminate SF6 from power grid infrastructure.

Sulfur hexafluoride has served as the standard insulating gas in high-voltage circuit breakers and switchgear for decades due to its exceptional dielectric properties. The gas presents a significant environmental problem: SF6 has a global warming potential 25,200 times greater than carbon dioxide over a 100-year period and persists in the atmosphere for approximately 3,200 years, according to the U.S. Environmental Protection Agency.

The Georgia Tech team, led by professor Lukas Graber, achieved arc interruption at 72 kilovolts using supercritical CO2, which operates above its critical point of 73 atmospheres and 31 degrees Celsius. At these conditions, carbon dioxide exhibits properties between liquid and gas phases, providing sufficient dielectric strength for high-voltage applications while eliminating the extreme greenhouse gas impact of SF6.

The European Union's updated F-gas Regulation, which took effect in 2024, mandates phaseout of SF6 in new medium-voltage switchgear by 2026 and restricts its use in high-voltage equipment. Utilities and equipment manufacturers face increasing pressure to identify alternatives that can match SF6's performance characteristics without its environmental consequences.

The Georgia Tech research team published results demonstrating successful arc interruption in a 72-kV class circuit breaker using supercritical CO2 as the insulating medium. The work represents the highest voltage rating achieved with this alternative technology to date.

ARPA-E's CIRCUITS program, which stands for Creating Innovative and Reliable Circuits Using Inventive Topologies and Semiconductors, provided funding for the research. The program specifically targets development of SF6 alternatives for grid-scale electrical equipment.

Professor Lukas Graber's team at Georgia Tech's School of Electrical and Computer Engineering conducted the testing at the university's high-voltage laboratory. The researchers demonstrated that supercritical CO2 could successfully interrupt fault currents at transmission-class voltage levels.

The prototype operates at pressures exceeding 73 atmospheres, the critical pressure of carbon dioxide. At these conditions, CO2 transitions to a supercritical state where it exhibits enhanced dielectric properties compared to its gaseous form at atmospheric pressure.

Figure 2: How the authentication bypass vulnerability works

The Georgia Tech researchers claim their supercritical CO2 circuit breaker achieved successful arc interruption at 72 kilovolts, matching the voltage class of many transmission-level circuit breakers currently using SF6. The team reported that supercritical CO2 provides sufficient dielectric strength for high-voltage applications when operated above its critical point.

According to IEEE Spectrum reporting, the supercritical CO2 approach offers advantages over other SF6 alternatives under investigation, including vacuum interrupters and alternative gas mixtures. The supercritical fluid provides both arc-quenching capability and dielectric insulation in a single medium.

The EPA documents SF6's global warming potential at 25,200 times that of CO2 over a 100-year timeframe. The agency notes that SF6 concentrations in the atmosphere have increased substantially since the 1970s, with electrical equipment representing the largest source of emissions.

EU regulatory documents confirm that the updated F-gas Regulation establishes binding timelines for SF6 phaseout in electrical equipment. Medium-voltage switchgear faces restrictions beginning in 2026, with high-voltage equipment subject to progressively stricter requirements through 2030 and beyond.

Supercritical CO2 circuit breakers could eliminate one of the most potent greenhouse gas sources in electrical infrastructure. Replacing SF6 with CO2 reduces the global warming impact of insulating gas leakage by a factor of more than 25,000.

The technology uses carbon dioxide, an abundant and inexpensive gas compared to manufactured SF6. Utilities would face lower costs for insulating gas procurement and potentially simplified handling procedures.

Successful demonstration at 72 kilovolts indicates the technology could scale to transmission-level applications. Grid operators managing high-voltage infrastructure would gain an alternative to SF6 that meets regulatory requirements without sacrificing performance.

The research positions American manufacturers to compete in markets where SF6 restrictions already apply. European utilities must comply with F-gas Regulation timelines, creating demand for alternative technologies.

Figure 3: Privilege escalation from user to SYSTEM level

Supercritical CO2 systems require operation at pressures exceeding 73 atmospheres, significantly higher than the 5-7 atmospheres typical of SF6 equipment. The elevated pressure requirements increase mechanical complexity and may affect equipment reliability.

The technology remains at prototype stage. Transitioning from laboratory demonstration to commercial products requires extensive engineering development, testing, and certification processes that typically span years.

Existing SF6 equipment represents decades of installed infrastructure. Utilities face substantial costs to replace functioning equipment, even when alternatives become available. The economic case for replacement depends on regulatory requirements, equipment age, and leak rates.

Supercritical CO2 does not match SF6's dielectric properties at equivalent pressures. Achieving comparable performance requires either higher operating pressures or larger equipment dimensions, both of which affect cost and installation requirements.

Circuit breakers protect electrical systems by interrupting fault currents, which can reach tens of thousands of amperes during short circuits. When contacts separate to break the circuit, an electrical arc forms between them. The insulating medium must extinguish this arc and prevent re-ignition while maintaining electrical isolation.

SF6 excels at arc interruption because its molecules capture free electrons, rapidly cooling the arc plasma and restoring dielectric strength. The gas also provides excellent electrical insulation, allowing compact equipment designs.

Supercritical CO2 operates above carbon dioxide's critical point: 31 degrees Celsius and 73 atmospheres. In this state, the fluid exhibits properties intermediate between liquid and gas. The higher density compared to gaseous CO2 improves dielectric strength, while the fluid nature allows it to flow and cool arc regions.

The Georgia Tech design maintains CO2 above its critical pressure throughout operation. When contacts separate during a fault, the supercritical fluid absorbs energy from the arc and provides the dielectric recovery needed to prevent re-ignition.

Technical context (optional): Dielectric strength measures a material's ability to withstand electric fields without breakdown. SF6 at atmospheric pressure has dielectric strength approximately 2.5 times that of air. Supercritical CO2 at 100 atmospheres approaches SF6's dielectric performance, though the pressure differential creates engineering challenges for equipment design.

The electrical equipment industry faces a fundamental transition away from SF6 over the coming decade. Regulatory pressure in Europe has already begun, and similar restrictions may emerge in other jurisdictions as climate policy evolves.

Equipment manufacturers including ABB, Siemens, and Schneider Electric have invested in SF6 alternatives including vacuum interrupters and alternative gas mixtures. The supercritical CO2 approach represents a distinct technical path that could compete with or complement these efforts.

Utilities managing aging SF6 equipment must plan for eventual replacement regardless of regulatory requirements. SF6 prices have increased as production faces scrutiny, and leak detection and reporting requirements add operational costs.

The research demonstrates that academic institutions can contribute meaningfully to grid infrastructure challenges. ARPA-E funding for high-risk, high-reward energy research enables exploration of approaches that commercial entities might not pursue independently.

The Georgia Tech team has not published detailed cost projections for commercial supercritical CO2 equipment. Economic viability depends on manufacturing costs, installation requirements, and maintenance needs that remain undefined at the prototype stage.

Long-term reliability data does not exist for supercritical CO2 circuit breakers. SF6 equipment has accumulated decades of operational experience, while the alternative technology has only laboratory testing history.

The pathway from 72-kV demonstration to higher voltage ratings remains uncertain. Transmission systems operate at voltages up to 765 kV, and scaling supercritical CO2 technology to these levels presents additional engineering challenges.

Regulatory acceptance of supercritical CO2 equipment has not been established. Standards organizations and grid operators must evaluate the technology before utilities can deploy it in critical infrastructure.

ARPA-E program reviews will provide updates on the Georgia Tech project's progress toward higher voltage ratings and commercial development partnerships. The agency typically publishes project outcomes and transition plans.

Equipment manufacturers may announce licensing agreements or development programs based on the supercritical CO2 approach. Commercial interest would signal industry confidence in the technology's viability.

EU F-gas Regulation implementation will create market pressure for SF6 alternatives. Utility procurement decisions in Europe will indicate which alternative technologies gain commercial traction.

Additional academic and industry research on SF6 alternatives will clarify the competitive landscape. Vacuum interrupters, alternative gas mixtures, and supercritical CO2 each have distinct advantages and limitations that ongoing research will illuminate.

1. IEEE Spectrum, "SF6 Circuit Breaker Alternative Uses Supercritical CO2," April 9, 2025. https://spectrum.ieee.org/sf6-circuit-breaker

2. U.S. Environmental Protection Agency, "SF6 Basics," EPA SF6 Emission Reduction Partnership for Electric Power Systems. https://www.epa.gov/eps-partnership/sf6-basics

3. European Commission, "EU Legislation to Control F-gases," Climate Action, updated 2024. https://climate.ec.europa.eu/eu-action/fluorinated-greenhouse-gases/eu-legislation-control-f-gases_en