H02H 3/335

Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection {; integrated protection } responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at corresponding points in different conductors of a single system, e.g. of currents in go and return conductors using summation current transformers {with means to produce an artificial unbalance for other protection or monitoring reasons or remote control the main function being self testing of the device}