Investigations on lightning impulse breakdown characteristics of SF6 N2 gas insulated 22 kV medium voltage circuit breaker

Abstract

Electrical power network is protected by the high voltage HV and medium voltage MV circuit breakers capable of making carrying and breaking currents under normal and fault conditions MV and HV circuit breakers are the key safety devices in electrical power network and they have to separate faulty parts of the grid fastly and reliably If the protective device does not function properly when an over load or short circuit occurs then there is a chance for fire and shunt down of entire power system Based on the nature of insulating medium used in the circuit breaker it can be classified as Air Circuit Breaker Oil Circuit Breaker Vacuum Circuit Breaker and SF6 Circuit Breaker SF6 gas insulation has an excellent insulating property and high electro negativity property ie high affinity of absorbing free electron Therefore when compared with other common gases available for insulation purpose overall mobility of the charged particle in the SF6 gas is much less The mobility of charged particles is majorly responsible for conducting current through a gas medium Hence SF6 gas gives very high dielectric strength This gas has good heat transfer property because of low gaseous viscosity SF6 is 100 times more effective as an arc quenching media than air circuit breaker The major advantage of this gas is that it has fast recovering and self healing property which is useful during arcing conditions of circuit breakers In addition decomposition by products of this gas can be easily filtered and removed It is used for both medium and high voltage electrical power system from 33 kV to 800 kV The fault interruption capability of MV and HV circuit breakers are increased over the last decades and now days SF6 circuit breakers capable of interrupting 20 GVA per unit are designed newline