Auxiliary test block for differential protection circuit breaker - permits remote operation of test circuit on circuit-breaker and has fuse and protective contact shunted by resistance lamp parts

摘要

The circuit-breaker (12) is equipped with differential protection consisting of a transformer (30) and polarised relay (32). A test circuit for the protection consists of current taps (36, 38) one on each side of the differential transformer, a resistance (40), a safety switch (44) and a test ush-button (42). The auxiliary block permits actuation of the test circuit from a remote point. Current tap points (20) lead into the block via conductors (16, 18), through respectively a fuse (46) and a resistance with protective contact (52) on to connectors (48, 54) and remote leads (24, 26) to push-button (28). The protective contact is actuated by a bimetal strip heated by the resistance. Both these, and also the fuse, are shunted by resistance-lamp paths (66, 68; 60, 62). In the event of faults developing on the remote leads (24, 26) or of over-long passage of test-path current, either the fuse or the protective contact operates and the coresponding lamp lights.