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In sulphur hexa fluoride ckt breaker, SF6 gas is used as the arc quenching medium. The SF6 is an electronegative gas and has a strong tendency to absorb free electron. The contacts of the breaker are opened. In a high pressure flow of SF6 gas an arc is struck between them. The conducting free electrons in the arc are rapidly captured by a gas to from relatively immobile ion. This loss of conducting electrons in the arc is quickly builds up enough insulation strength to extinguish the arc. The SF6 ckt breakers have been found to be very effective for high power and high voltage service.