GB1237862A - Monitoring electric switch contact operation - Google Patents

Abstract

1,237,862. Monitoring switch operations. ENGLISH ELECTRIC CO: Ltd. June 17, 1968 [June 20, 1967], No.28315/67. Heading G1U. In an arrangement for monitoring the operation of switch contact arrangements connected in parallel connected electric circuits which have substantially different impedances when contacts are closed, e.g. as in a circuit breaker 22 incorporating main interrupters 26, 27 and auxiliary interrupters 28, 29 in series with resistors 30 respectively across the main interrupters, a separate monitoring circuit 16-19 is provided for connection with each such electric circuit. Each monitoring circuit includes in series relation an A.C. test signal source, a test signal response monitoring arrangement for presenting an indication of the state of the associated switch contact arrangement and rectifier arrangements 33 preventing interaction between the test signal sources. Impedance matching arrangements 32 are associated with one or more monitoring circuits to match the impedances of the associated electric circuits such that the respective impedances to the flow of current in the monitoring circuits are less than a given value when the respective contact arrangements are closed. The separate A. C. sources are provided by respective secondary windings on a transformer 2 whose primary is coupled to a signal generator 1. The monitoring arrangement incorporates respective transformers 9 connected in the monitoring circuits, with secondaries connected to styli 13, which mark a moving sensitive paper 15 when current flow in the monitoring circuits is above a given amount, i.e. when the corresponding interrupter is closed. The impedance matching arrangements are transformers 32 with full bridge rectifiers 33 in their secondary circuits providing,current isolation between the separate monitoring circuits. Due to the impedance matching, each monitoring circuit responds only to the condition of the associated interrupter.