On new DC vacuum circuit breaker based on artificial current zero

An improved scheme is proposed based on the conventional artificial current zero vacuum DC circuit breaker.By means of a reverse parallel diode connected with the vacuum switch,a zero voltage period of vacuum dielectric recovery can be obtained after the current zero due to the free-wheel of the diode.This greatly improves the dielectric strength of the vacuum gap thus to enable the vacuum switch to break the highly-rising short-circuit current in an thin vacuum gap.As a result the current limiting and breaking abilities of the DC circuit breaker are enhanced.A prototype of the new circuit breaker is designed,which has been used for short circuit tests.The results show that the circuit breaker can limit a short circuit current with initial di/dt of 20 A/μs under 10 kA in less than 1.1 ms and meet the demand of protecting modern ships in short-circuit conditions.