Breaking principle: self expansion LF circuit breakers use the SF6 gas self expansion technique. This technique is the result of many years’ experience in SF6 technology and major research work. It combines the effect of thermal expansion with a rotating arc to create arc blowing and quenching conditions. The result is reduced control energy requirements and arcing contact erosion; this increases mechanical and electrical endurance. The operating sequence of a self-expansion breaking chamber, whose moving part is driven by the mechanical operating mechanism, is as follows: