GB271443A - Improvements relating to indicating systems for dynamo-electric machines adapted to be connected to a common bus-bar - Google Patents

Abstract

271,443. British Thomson-Houston Co., Ltd., (Assignees of Finney, A. C.). May 21, 1926, [Convention date]. Protective arrangements.-A green lamp 27 is illuminated when none of the alternating current generators 3 - - 6 is connected to the bus-bar 7, and a red lamp 22 is illuminated when two or more of the generators are connected by their associated switches 13 - - 16 to this bus-bar. The generators are connected to the supply bus-bar 9 through switches 8, only one phase being shown, and the bus-bar 7 is the earthed neutral, it being desirable to have not more than one generator connected thereto because of the possibility of circulating currents, especially those of triple frequency. When all the switches 13 - - 16 are open, the associated series connected contacts 12 are bridged and the lamp 27 is illuminated from a supply 23. Closure of any switch breaks the circuit, and completes another at the associated contacts 17 through a resistance 26 and coil 19 of a differential relay, but the current through this coil is insufficient to cause movement of the relay. However, if two or more of the switches 13 -- 16 are closed, then a corresponding number of resistances 26 are connected in parallel, and consequently the current through the coil 19 is increased sufficiently to cause closure of the relay contacts 20, 21 and the illumination of the lamp 22. In a modification the contacts 12 are omitted and the relay is provided with centering springs, so that with no switches closed, one relay contact is closed to illuminate the green lamp and' also ring a bell, with two switches closed the relay is centred, and with more than two another contact is closed to illuminate the red lamp and ring another bell.