Arc transfer in a rotary arc circuit breaker

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 high-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 authors report 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. 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