News From Japan

Abstract

Sulfur hexafluoride (SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) gas, which is non-toxic, non-flammable, colorless, and odorless, is an important gaseous dielectric medium for high-voltage switchgear, circuit breakers, and other electrical equipment since it is known to have a much higher breakdown strength than air or dry nitrogen and an excellent arc extinguishing ability. However, it has a global warming potential of 25,200 times that of CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Because of this, it is desirable to develop high-voltage and high-capacity apparatuses that do not or rarely use SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> gas. From this view-point, Meidensha, Tokyo, has been developing vacuum circuit breakers, as reported in this News from Japan column in the January/February 2015 issue [1]. The vacuum circuit breaker mentioned in [1] used SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> for electrical insulation, although a vacuum was used for its interrupters. Recently, Meidensha has developed a 145-kV dry-air-insulated vacuum circuit breaker for the first time [2]. This short article provides an overview of its development.