Protective distance relay system for power transmission lines

Claim 1

A PROTECTIVE RELAY SYSTEM COMPRISING FIRST AND SECOND DISTANCE RELAYS CONNECTED TO OPPOSITE ENDS OF A SECTION OF POWER LINE AND EACH OPERATIVE TO ACTUATE A SWITCH FOR TRIPPING A LINE CIRCUIT BREAKER ADJACENT ITS END OF THE SECTION, EACH RELAY INCLUDING A NON-DIRECTIONAL ELEMENT FOR TRANSMITTING A CONTROL SIGNAL TO THE OTHER RELAY UPON A FAULT OCCURRING WITHIN A DISTANCE WHICH EMBRACES ALL OF A NUMBER OF ZONES OF PROTECTION EXTENDING FROM BOTH RELAYS, THE ZONES OF EACH RELAY BEING UNIDIRECTIONAL AND TOGETHER EXTENDING OVER THE WHOLE OF SAID SECTION, CIRCUIT MEANS AT EACH RELAY FOR BOTH EXTENDING THE INITIAL ZONE OF THE RELAY AND INHIBITING SAID BREAKER FROM TRIPPING UPON RECEIPT OF SAID SIGNAL BY THAT RELAY, AND A DIRECTIONAL ELEMENT IN EACH RELAY FOR BOTH INTERRUPTING THE TRANSMISSION OF SAID SIGNAL AND ACTUATING SAID SWITCH UPON DETECTION BY THAT RELAY OF A FAULT WITHIN ANY OF ITS ZONES OF PROTECTION, THE ARRANGEMENT BEING SUCH THAT SAID INTERRUPTION OF TRANSMISSION AT ONE RELAY UNINHIBITS THE BREAKER AT THE OTHER RELAY WHEREBY TO PERMIT SAID DIRECTIONAL ELEMENT OF SAID OTHER RELAY TO CAUSE ITS BREAKER TO TRIP UPON DETECTTION OF A FAULT IN ANY OF ITS ZONES.