Mutual impedance compensation for distance relaying

Claim 1

IN A RELAYING NETWORK FOR PARALLELY ARRANGED POLYPHASE ELECTRICAL TRANSMISSION NETWORKS, FIRST AND SECOND SETS OF CURRENT INPUT TERMINALS ADAPTED FOR CONNECTION TO A FIRST AND SECOND ONE OF SAID NETWORKS, EACH SAID SET COMPRISING A PLURALITY OF TERMINALS, SAID TERMINALS OF SAID FIRST SET BEING OPERATIVELY CONNECTED TO THE PHASES OF SAID FIRST NETWORK, SAID TERMINALS OF SAID SECOND SET BEING OPERATIVELY CONNECTED TO THE PHASES OF SAID SECOND NETWORK, A ZERO SEQUENCE CURRENT RESPONSIVE RELAY HAVING INPUT AND OUTPUT CONNECTIONS, MEANS CONNECTING SAID INPUT CONNECTIONS OF SAID RELAY TO SAID SECOND NETWORK TO RESPOND TO THE FLOW OF ZERO SEQUENCE CURRENT THEREIN, SAID RELAY BEING OPERABLE IN RESPONSE TO THE FLOW OF A ZERO SEQUENCE CURRENT THROUGH ITS SAID INPUT CONNECTIONS OF A MAGNITUDE IN EXCESS OF A PREDETERMINED MINIMUM MAGNITUDE TO PLACE ITS SAID OUTPUT CONNECTIONS IN A FIRST CONDITION, A MAGNITUDE COMPARISON NETWORK HAVING FIRST AND SECOND PAIRS OF INPUT TERMINALS AND A PAIR OF OUTPUT TERMINALS, SAID COMPARISON NETWORK BEING CHARACTERIZED BY THE ABILITY TO PROVIDE A FIRST OUTPUT SIGNAL AT ITS SAID OUTPUT TERMINALS WHEN THE MAGNITUDE OF A FIRST ELECTRICAL SIGNAL APPLIED TO ITS SAID FIRST PAIR OF INPUT TERMINALS HAS A PREDETERMINED RELATION TO THE MAGNITUDE OF A SECOND ELECTRICAL SIGNAL APPLIED TO ITS SAID SECOND PAIR OF INPUT TERMINALS, FIRST AND SECOND SIGNAL GENERATING DEVICES, EACH SAID SIGNAL DEVICE HAVING INPUT MEANS AND OUTPUT MEANS, A FIRST CIRCUIT CONNECTING SAID TERMINALS OF SAID FIRST SET TO SAID INPUT MEANS OF SAID FIRST SIGNAL DEVICE TO ENERGIZE SAID DEVICE WITH AN ELECTRICAL QUANTITY PROPORTIONAL TO THE ZERO SEQUENCE QUANTITY FLOWING IN SAID FIRST SET OF TERMINALS, A SECOND CIRCUIT CONNECTING SAID TERMINALS OF SAID SECOND SET TO SAID INPUT MEANS OF SAID FIRST AND SAID SECOND SIGNAL DEVICES