GB610948A - Improvements in or relating to the protection of alternating current power systems - Google Patents

Abstract

610,948. Protective cut-out systems; electromagnetic relays. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. April 15, 1946, No. 11482. Convention date, April 16, 1945. [Class 38 (v)] A circuit-breaker 13 connecting an A.C. generator 10 to a load bus 12 is tripped instantaneously in the event of reduced frequency. but only after a time delay on reduced voltage. A frequency relay 16 comprises contact members 23, 26 biassed to a central position, as shown, and actuated by armatures 18, 19 to disengage a contact 27 on low frequency and appreciable voltage in lines 28, 29 or to engage a contact 25 on normal frequency and voltage. A timedelay relay 17 comprises a motor 31 which drives a cam 32 through a de-energized magnetic clutch 33 to open contacts 54, the clutch being spring-biassed into engagement. When the output from the generator 10 has attained normal frequency and voltage, a control relay 45 is energized through contacts 23, 25 so that closure of a manual switch 44 to contact 46 energizes the closing coil 14 of the circuitbreaker 13. Reduced voltage in the lines 28, 29 without any appreciable reduction in generator speed, opens contacts 23, 25 and de-energizes the clutch 33, thereby energizing the motor 31 through contacts 27, 26, 58, 37, 38 and opening the relay 45 when the contacts 54 open. As relay 45 opens, it energizes a trip coil 15 on the circuit-breaker 13. When the clutch 33 is again energized, a restoring spring 42 returns the cam 32 to normal. Reduced frequency in the lines 28, 29 without any appreciable voltage reduction also opens the contacts 26, 27, thereby opening the holding circuit 52, 58, 55 of the relay 45 and energizing the trip coil.