GB436136A - Improvements in or relating to starting systems for electric motors or other electric apparatus - Google Patents

Abstract

436,136. Control of D.C. andA.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. May 17, 1935, No. 14504. Convention date, Mav 18, 1934. [Class 38 (iii)] Self reducing resistance 6 is connected in series with an electric motor or similar apparatus 1 to prevent excessive starting current, and a repeated switching - in before the resistance is sufficiently cooled is prevented by automatically rendering inoperative the operating coil 9 of an electromagnetic switch 7 in the main circuit. The coil 9 may be connected in parallel with an additional selfreducing resistance 12 which carries current during the whole of the working period, so that, after the main circuit is opened, the resistance 12 must cool sufficiently to allow an operative current to flow through the coil 9 when the circuit is reclosed. A resistance 13 in the circuit of the resistance 12 is dimensioned so that the resistance 12 cools sufficiently only after the resistance 6 is sufficiently cooled to control the motor 1 effectively. In a modification the self-reducing resistance in the main circuit serves also to control the coil 9. In this arrangement, Fig. 2, not shown, the coil 9 is connected across the self-reducing resistance in the main circuit when the switch 7 is opened, and disconnected therefrom when the switch is closed. The arrangements are applicable to three-phase supplies, and in further modifications, Fig. 3, not shown, the circuit of the coil 9 includes contacts of a thermal switching element heated either by the main current or by the heat of the selfreducing series resistance.