Challenging the energy industry on SF6

Carbon dioxide may be the most well-known pollutant, yet it is just one of a stew of six atmospheric damaging greenhouse gases that cause climate change by trapping the earth's heat. Some greenhouse gases hide in products the utility industry uses every day and of which many of their employees, much less the public, have no knowledge.

Clear, odorless, and tasteless, SF6 can have a strong impact on global warming. Commonly used as insulation in utility plant conductors or "breakers," the U.S. Environmental Protection Agency declares SF6 may be "the most potent greenhouse gas known to date."

The agency says on its website that "over a 100-year period, SF6 is 22,800 times more effective at trapping infrared radiation than an equivalent amount of carbon dioxide (CO2)." With a staying power of more than 3,200 years, SF6 outlasts carbon dioxide's 1,600-year longevity. At least photosynthesis reduces CO2’s atmospheric life to just over 20 years. SF6 never loses its destructive potency.

Nor does SF6 show signs of becoming less of a problem. On the contrary, quarterly carbon data on SF6 collected by the National Oceanic and Atmospheric Administration shows levels frequently rising over the past few years and conceivably, SF6 is becoming as problematic as CO2.

Established in the 1960s, the California Air Resources Board (CARB) has been an innovator in reducing air pollution from vehicles and other sources. A successful cap-and-trade program it developed also drives down emissions from natural gas distribution, electricity generation, transportation fuels and industries. In addition, the agency set a goal for utilities of removing SF6 by first requiring them to start the phase-out of new SF6 purchases in 2024.

By 2033 CARB wants utilities to stop buying any SF6-insulated products. However, all existing SF6 installations would be allowed to operate until their end of life. The regulation provides a coordinated effort and an agreed schedule for removing SF6 that CARB reached with input from power companies, environmental organizations, and equipment manufacturers.

Pacific Gas & Electric Company (PG&E), California's largest utility, has been a national leader in reducing carbon emissions for years – despite unrelated recent negative publicity this year involving its role in wildfires. In July 2019, the company announced an initiative to eliminate one million metric tons of emissions from its operations, with part of that goal involving an earlier purchase of SF6-free high-voltage products from Siemens Energy. The purchase agreement included dead-tank circuit breakers up to 115 kV and gas-insulated switchgear (GIS) for 115 kV, 50 kA.

Siemens Energy is an international leader in developing SF6-free high-voltage products with zero-global warming potential (GWP). "Siemens Energy has been investing very heavily for over a decade in alternative technologies that remove SF6 gases," said Sohail Muhammad, Vice President of switching products for Siemens Energy North America. Speaking at the Siemens Energy Week USA earlier this year, he said the SF6-free or zero-global warming potential products "replace a very highly potent gas with a Clean Air solution that provides reliability and provides environmental capabilities in terms of climate neutrality."

The collaboration with PG&E, however, is vital for Siemens Energy. As Sohail highlighted in his discussion, the company has competitors in the SF6-free marketplace. Before the deal, the utility had already switched from SF6 to cleaner technologies for lower voltage levels. However, CARB's legislative target made it imperative the PG&E begin replacing high-voltage SF6 equipment with F-gas-free solutions.

A revised CARB regulation was required because California saw no improvement after regulating SF6 emissions for years, according to Tom Rak, the former manager of substation and T-Line standards engineering at PG&E. "The emissions of SF6 into the atmosphere have not gone down in California even though we have tightened up on our leak rates," he said. "It simply has to do with the fact there is just so much new SF6 going on to the grid that the volume of emissions has not gone down."

That will begin to quickly change over the next decade as the state's utilities switch to zero-GWP or F-gas-free conductors, live-tank and dead-tank breakers, and insulated busducts and gas-insulated switchgear (GIS). The new equipment will be less expensive to operate and manage than SF6-based technologies. "This is where utility investment and government regulation is heading – toward a global warming-free solution," Rak said.

Invented in 1901, SF6's first commercial use in the utility industry came decades later, in 1956. Before SF6 became widely available, utilities break switches had atmospheric air or oil as insulation. 

The SF6 technology reduced the risk of fire and explosion and reduced the size of the equipment. The high global warming potential was handled by closed material loops with low emissions.

With the increasing installation volume of SF6, its long life time and the demand to eliminate greenhouse gases to fight climate change, a new switching and insulation technology without any greenhouse gases has been developed. Vacuum and atmospheric air breakers compete in the breaker marketplace, but SF6 remains the most popular choice for most utilities despite the serious drawbacks. For example, PG&E's research found SF6 breakers are expensive to maintain because employees and contractors must wear complete scuba equipment to fix that equipment.

An SF6 leak costs PG&E an average of $25,000. California's regulations call for the utility to maintain a leak rate of less than 1%, leading to a situation that requires considerable and expensive leak testing. After buying equipment from one vendor, PG&E found it had to spend an additional $1 million to rework equipment to meet the 1% leakage threshold, according to an article in a 2020 T&D World article penned by Rak.

Rak’s article describes how and why the utility invested in dry-air/vacuum technology that underpinned the Siemens Energy contract for circuit breakers that use treated air, or "Clean Air," as the insulating medium along with vacuum interrupters for switching functions. While the utility chose siemens Energy technology, he noted that other companies also have similar dry/vacuum product offerings.

Rak spent the past summer traveling the Mediterranean Sea on a sailboat, visiting Croatia, Montenegro, Albania, and the Greek islands. His sparse LinkedIn profile names his job as "sea captain" in San Francisco who occasionally consults on SF6 issues. As he studies the range of responses to SF6, Rak said PG&E is far from the only utility working to remove the compound from their process. Other states have joined California in regulating SF6 as a greenhouse gas.

"Society as a whole is starting to realize that our past efforts to address climate change are failing or have failed," Rak said. "The revised effort is to eliminate the use of all climate change gases. We can eliminate three man-made climate change gases completely, and SF6 is one of them".