GB857024A - Improvements in and relating to electrical protective or alarm arrangements - Google Patents

Abstract

857,024. Protective cut-out arrangements; thermal switches. ENGLISH ELECTRIC CO. Ltd. Oct. 21, 1957 [Oct. 19, 1956], No. 31838/56. Class 38 (5). In a protective or alarm arrangement, particularly for semi-conductor rectifier installations, any one of a plurality of fault-indicating devices responds to fault conditions in the protected circuit and at the same time as an alarm or tripping-device which is common to all the fault-indicating devices. In Fig. 1, the D.C. bus-bars 10, 11 are connected to the rectifier phases by conductors 12 and series striker-pin fuses 13. When any fuse 13 blows, its spring-biased pin 14 displaces a bar 15 against light compression-springs 17 to actuate the micro-switch 18. Alternatively main fuses fuses (Fig. 3, not shown) may be shunted by fuses of the striker-pin type but having lower current rating and arranged to operate in the manner described. The micro-switch contacts of a number of units are arranged when actuated to complete respective circuits a-a . . . d-d, so as to light a lamp 20 from the tapped transformer 28. Other lamps 20 are not lit since they are each effectively in series with two resistors 21. The bridge-rectifier connected relay 24, however, is energized, in series with one resistor 21, so that it opens contacts 24a to de-energize the coil 26 of the rectifier input contactor (not shown), closes contacts 24b to operate an alarm hooter 27 and closes contacts 24c for remote indicating or protective gear. Operation of a push-button 30 will then energize a relay 31 having contacts 31a, 31b arranged to disconnect the hooter 27 and " hold in the relay 31 until the contacts 24b are opened. Operation of the respective switch 32 of the lighted lamp disconnects the relay 24 which resets and is ready to operate in response to further fault conditions. The left-hand lamp 20 is energized by the operation of switches 34 controlled by the flow of cooling fluid to the rectifier. Testing push-buttons 33, 30a are provided; the former to disconnect the relay 24 and light all the lamps 20 and the latter to energize the hooter 27.