While coal-fired power plants continue to be portrayed as the primary target of carbon dioxide regulation, emissions of a lesser known but more potent greenhouse gas from the electric utility industry is being regulated for the first time in California.

Sulfur hexafluoride (SF6) is a colorless, odorless, non-toxic, and non-flammable gas that has been used in the electric utility industry in the United States since the 1950s. However, because SF6 has a 100-year global warming potential (capacity to heat the atmosphere) that is more than 22,000 times that of carbon dioxide and an atmospheric lifetime of 3,200 years, it is by far the most potent of all recognized greenhouse gasses.

Primarily used in electricity transmission and distribution systems as an insulator and arc interrupter for circuit breakers, switchgear, and other electrical equipment, emissions of SF6 occur during equipment installation, servicing and disposal, as well as escaping through seals in older equipment. SF6 largely replaced flammable insulating oils -- its advantages include allowing for more compact substations in urban areas. The EPA says that currently there are no available substitutes for SF6 in this application.

California First to Act

By virtue of a vote of its Air Resources Board in February, California became the first jurisdiction to formally regulate SF6 emissions from electrical equipment in the United States. Starting in 2012, owners of equipment containing SF6 will be allowed to leak no more than 10% of their total capacity into the atmosphere. The cap will decline until they reach the ultimate target of 1% of their SF6capacity in 2020 – which equates to a 70% reduction of SF6 emissions from all electric utility applications in the state.

The regulations exempt several other uses of SF6, including medical uses, nuclear power plant testing and equipment calibration. Everyone else will be prohibited from purchasing, selling, owning or using SF6in the state after January 2011. The Air Resources Board estimated that the rule would affect 75 utilities, government agencies and other owners of electrical equipment. The cost of implementing this measure has been estimated to be $4.5 million to $7 million over the 10-year period, which is anticipated to result in an increase in electricity rates of 1 to 2 cents per year.

Compliance will be achieved through plugging leaks, recycling the gas, and refurbishing or replacing equipment. Through improvements in the leak rate of new equipment, refurbishing of older equipment and the use of more efficient operation and maintenance techniques, utilities can over time find more economical solutions to reduce SF6 emissions.

Actions at the Federal Level

The electric transmission and distribution industry has already been working with the U.S. Environmental Protection Agency (EPA) on this issue for more than a decade. A voluntary industry-EPA program called the SF6Emission Reduction Partnership was initiated in 1999 with 49 charter partners from the electric utility industry. The program’s primary objective is to share information and resources to reduce SF6emissions via cost-effective technologies and practices. Partners agree to estimate current and annually inventory actual emissions using an established protocol; establish a strategy for replacing older leakier pieces of equipment; implement SF6 recycling; and ensure that only knowledgeable personnel handle the gas. Each partner submits annual progress reports to the EPA. Overall, the Partnership’s SF6emission rates4 have dropped from 17% in 1999 to 6.5% in 2006. During this time the Partnership has grown to 77 members representing more than 45% of the industry.

Meanwhile, the EPA has been busy developing its own mandatory regulatory regime to address SF6 emissions. The agency had originally proposed to include leaks of SF6 from electrical equipment in its mandatory reporting rule that came into effect on January 1, 2010, but chose to defer requiring annual inventories until additional analysis of data collection procedures and methodologies. As of mid-March, EPA had completed drafting these rules and they had been cleared by the Office of Management and Budget.

Convergence of EPA and California Initiatives

The efforts and advances from EPA’s program will hopefully make compliance with the new California requirements more feasible. Five California utilities are members of the SF6Emission Reduction Partnership, including Pacific Gas and Electric (PG&E) which was one of the first companies to join the EPA’s voluntary program in 1999. After discovering that more of its equipment was leaking than the company previously thought, PG&E implemented an enhanced leak detection program that included use of a laser camera to identify leaks, which more than paid for itself through cost savings gained by leak reductions. By 2009, PG&E reported that its SF6leak rate had been reduced by more than 50% since 1998.

— Andy C. Byers, associate vice president, Black & Veatch

4 Emission rate relative to the total amount of SF6 containing electrical equipment (calculated by dividing total emissions by total nameplate capacity).

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