Arc transfer in a rotary arc circuit breaker

Abstract

Rotary arc circuit breakers interrupt low-level fault currents through the extinction of a free burning arc between the load current contacts but utilise an electromagnetic field for spinning the arc, transferred into a coil, for interrupting higher-level fault currents. The operation of such circuit breakers relies upon using the arc additionally for switching the coil into the circuit to produce the arc-controlling magnetic field. The paper reports the results of investigations into factors which affect the transfer of the arc root from the load current carrying contact to the annular contact that supports the arc during electromagnetic rotation and simultaneously allows the magnetic field producing coil to be activated. The influence of a number of parameters is considered including the peak arc current, point on wave switching, nature and pressure of the arcing medium and the contact/coil geometry. The results show that for SF6, in the current range of several hundred amperes, the arc transfer time may be prolonged by as much as 25 ms. However, by suitable design of the contact/coil geometry, this arc transfer time may be substantially reduced to promote improved circuit breaker performance through an earlier interruption of the fault current.