Electricity Transmission and Distribution Greenhouse Gas Emissions
In 2007, the California Air Resources Board (CARB) approved the reduction of sulfur hexafluoride (SF6) emissions from electricity transmission and distribution equipment as an early action measure. This was required by the Global Warming Solutions Act of 2006 (Assembly Bill 32). CARB adopted the Regulation for Reducing Sulfur Hexafluoride Emissions from Gas Insulated Switchgear in 2010, which requires switchgear owners to reduce their emission rates, reaching a 1 percent emission rate by 2020.
SF6 is a potent greenhouse gas; over a 100-year period, SF6 is 22,800 times more effective at trapping infrared radiation than an equivalent amount of carbon dioxide. SF6 is also a very stable chemical, with an atmospheric lifetime of 3,200 years. Although considerable progress has been made in the past decade to develop non-SF6 gas-insulated equipment (GIE), new technologies have not been widely adopted. In order to drive this transition, CARB amended the regulation in 2021 to phase out the acquisition of SF6 GIE. Other changes are also adopted to cover other greenhouse gases beyond SF6 and enhance accuracy of emissions accounting and reporting. The amended regulation became effective January 1, 2022.
The most common use for SF6 is as an electrical insulator in high-voltage equipment that transmits and distributes electricity. Since the 1950s, the U.S. electric power industry has used SF6 widely in circuit breakers, gas-insulated substations, and other switchgear used in the transmission system to manage the high voltages carried between generation stations and customer load centers. Fugitive emissions of SF6 can escape from gas insulated substations and switchgear through seals and can also be released during equipment installation and when equipment is opened for servicing.
Manufacturers of gas-insulated equipment now offer market-ready non-SF6 GIE or have announced plans to develop them in the future. When establishing a timeline for phasing out acquisition of SF6 GIE in California, CARB staff consulted with manufacturers currently developing non-SF6 GIE to learn when their products are expected be commercially available. Three common types of alternative GIE that do not use SF6 are vacuum-solid dielectric, vacuum-dry air, and alternative gases. In order to ensure that there is a competitive marketplace for non-SF6 GIE, to reduce costs for these devices, and in response to stakeholder comments, CARB staff based the phase-out schedule in the regulation on the anticipated dates when two or more manufacturers have stated that non-SF6 GIE will be available plus an additional three-year period to ensure the new products are safe, reliable, and deployable.