Full Title

Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection (specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems H02H7/00; systems for change-over to standby supply H02J9/00 ) > 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 (H02H3/347 takes precedence)