GB853304A - Improvements in and relating to pilot circuit protection - Google Patents

Abstract

853,304. Protective arrangements. METROPOLITAN-VICKERS ELECTRICAL CO. Ltd. May 22, 1957 [May 25, 1956], No. 16273/56. Class 38 (5). In a protective arrangement a D.C. pilot circuit is supervized by the application of an A.C. signal to the pilot wires for the operation of an A.C. responsive device when the pilot circuit becomes defective. In the intertripping arrangement shown, a trip relay 3 at station B is energized from a D.C. source 2 at station A when intertrip contacts 4 are closed. The contacts 4 are normally open and are interconnected with normally closed contacts 6. An A.C. source 5 is connected in series with the pilot circuit at station A and a winding 7 of a wattmetric induction-type relay WR is connected in series with the pilot circuit at station B, a further winding 8 of the relay WR is supplied from an external source. Under normal conditions, the windings 7 and S are energized and maintain contacts 9, 10 open. If the pilot circuit is interrupted or the wires 1 become short-circuited, the winding 7 is de-energized and contacts 9, 10 close after time delay produced by the braking action due to a permanent magnet (not shown) to complete a detecting, indicating, controlling or supervizing circuit 11. A reversal of the pilot wires will reverse the torque of the relay WR and cause the contacts 9, 10 to close.