GB766032A - Improvements in the thermal protection of dual voltage electric motors - Google Patents

Abstract

766,032. Control of A.C. motors. GENERAL ELECTRIC CO. March 30. 1955 '[March 31, 1954], No. 9291/55. Class 38(3) A bimetallic protective element for a dual voltage motor is subjected to the same current at both operating voltages, and will therefore open the motor circuit at substantially the same temperature of the motor windings whichever voltage supply is used. As shown, for operation at the lower voltage, the running windings 3, 4, of the motor are connected in parallel, and a bimetallic disc 14 and heater 16 are in series with winding 4. A starting winding 9 is disconnected by a centrifugal switch when the motor reaches a predetermined speed. Deflection of the disc 14 will diengage a movable contact 13 from stationary contacts 12, 21, and so de-energize both running windings of the motor. When operating at the higher voltage, the disc 14, heater 16, and both the windings 3, 4, are connected in series so that the bimetallic disc carries substantially the same current as in the previous arrangement. As shown, the current in the starting winding 9 passes through the disc 14 and heater 16. However, in another arrangement, the starting circuit does not include the disc or heater, Fig. 3 (not shown). In a further modification, the starting current flows through the disc but not the heater.