Sulfur Hexafluoride (SF6): A GHG and Environmental Challenge

What is SF6?

Sulfur Hexafluoride or SF6 is an artificial gas commonly used in high voltage electrical equipment such as circuit breakers and substation switchgear, primarily as an insulation medium due to its great arc quenching characteristics.

What about discharges?

In most instances SF6 is contained in closed systems that remain sealed throughout the equipment’s entire lifespan. Actual SF6 discharges predominantly occur during manufacturing, installation, or subsequent maintenance. Consequently, equipment dismantling generally poses a more significant problem than actual leaks from previously installed products. As new apparatuses have improved over the last few years, leak rates have decreased with each new generation.

 

How about the by-products?

Arcing processes that are part of everyday operation of equipment (e.g. circuit breaker operation) cause the decomposition of SF6 into highly corrosive and toxic by-products. These decomposed by-products react with the inner components of the equipment and reduce surface stability, causing major breakdowns to occur. A critical prerequisite to form these decomposed by-products are reactants like water (H2O) and air (N2O).

Why does SF6 remain an environmental issue particularly given the focus on CO2 emissions?

Sulfur hexafluoride is one of the strongest green house gases noted by the Kyoto protocol. It can potentially impact global warming by a factor about 23,900 times larger than that of carbon oxide, CO2 emissions. Despite concerted efforts over a number of decades, the international science community and equipment manufacturers have not been successful in finding a more environmentally benign substitute. Globally, industry manufactures about 7,500 tons of SF6 each year, approximately 25 % of which is used in new electrical apparatus. The balance of production is used to compensate for leakage in old electrical apparatus. The total global leak rate has been estimated at 5 to 6 thousand tons per year.

How is SF6 Controlled?

The equipment manufacturers, service companies, and utilities using SF6-based equipment ensure that any equipment with SF6 is properly handled during inspection, maintenance, repair, and replacement/ recycling activities  ensuring strict compliance with applicable environmental authorities.