Apparatus for providing distance protection and distance measurement for a high voltage transmission line

Abstract From the Canadian patent

A protective relay for detecting faults in electrical power distribution system generates a signal .DELTA.i(t) which is substantially equal to the magnitude of the power distribution system current i measured at a first time subtracted from the magnitude of the power distribution system current i measured at a second time, the second time occurring later than the first time. The signal .DELTA.i(t) is utilized to generate measurement of the distance of a fault to the relay and is also utilized to generate operate signals if the fault occurs within the zone protected by the relay.