Improvements in Braking Polyphase Induction Motors

• Main Author: RUDOLF BRAUN
• Format: Patent
• Language: English
• Published: 25.10.1906

22,195. Braun, R. Oct. 31. Motors, controlling. -A polyphase induction motor is braked by converting it into a continuouscurrent generator by disconnecting the primary member from the alternating-current source and connecting either the primary or secondary member to a source of direct current, the circuit of the other member being closed either upon itself or through a regulating-resistance, the braking effect being regulated by varying either the direct-current supply or the resistance in the circuit of the shortcircuited member of the motor. In the case of a three-phase induction motor 1 connected to the source of supply 2, 3, 4 by means of the switch 5, a three-way switch 6 connects the motor to a direct-current source 7 and regulating-rheostat 8. The contacts 9, 10 of the switch are connected together and to one terminal of the direct-current source 7. To brake the motor, the switch 5 is opened and the switch 6 is closed, the directcurrent supplied to the motor being adjusted by - means of the rheostat 8. The rotor then rotates in a stationary field and generates a current dependent upon the resistance of the rotor winding. In the case of a motor supplied with slip-rings connected by an adjustable, resistance, the braking effect may be further regulated by varying the resistance in the armature circuit. The terminals of the three-phase motor winding may be con. nected to the direct-current source at different points of the delta or star formation, and, in the case of a two-phase motor,-either phase may be excited alone or the two-phase windings in series. Parts only of the motor windings may be connected to the direct-current source. The invention is particularly applicable for producing a constant creeping speed in motors connected to winding- engines &c. In the case of high-tension motors, it is preferable to connect the direct-current source to the secondary winding of the motor. The direct-current source may be a separately-disposed shunt-wound generator, or a series generator mechanically coupled to the winding-engines. To avoid sparking when the direct-current source is disconnected, the direct-current voltage is first reduced to zero by increasing the resistance in the shunt field or by short-circuiting the series field.