GB180075A - Improvements in and relating to the operation of alternating-current repulsion motors - Google Patents

Abstract

180,075. British Thomson - Houston Co., Ltd., (General Electric Co.). Feb. 23, 1921. Alternating-current commutator machines.- For dynamically braking a repulsion motor, the exciting component of the stator winding is connected across the supply line and the com. pensating part of the stator winding is connected in parallel with the exciting winding with reversed polarity, the result being that up to a certain speed the machine runs with shunt, characteristics and beyond this speed a braking induced current flows in a closed circuit through the stator coils. As shown in Fig. 1, the exciting and compensating coils 13, 14 are connected to the mains 15 through a resistance 16 and coupled single and doublepole switches 17, 18, 19. For normal running, the switches are thrown to the left, the circuit being through the blade 19, coils 14, 13, resistance 16, and blade 17. For braking, the switch is thrown to the right so as to connect the exciting winding 13 to the mains at 17, 18 and the compensating coil 14 in parallel with the coil 13 through the conductor 19<1>, sufficient resistance being included at 16 to limit the current to the desired value. In the form shown in Fig. 2, a relay 25 is included in the braking circuit to open the connection of the intermediate switch blade 18 to the exciting coil 23 when the braking current reaches a predetermined value. When this occurs, the stator windings are cut off from the line and the motor continues to give a braking torque by running as a self-excited generator. An alternative form is shown in which the motor runs on an autotransformer connected across the line instead of running directly on the line as in Fig. 2. The method is particularly applicable to crane motors where the lowering of the load is controlled by braking action.