GB725852A - Improvements in or relating to variable voltage motor control systems - Google Patents

Abstract

725,852. Exciting dynamo-electric machines. IGRANIC ELECTRIC CO., Ltd. April 8, 1953 [April 17, 1952], No. 9535/53. Class 35. [Also in Group XXXVII] A variable voltage system for hoists comprises a compound motor M having a separatelyexcited field winding 13 and a series field winding 32 which is connected in series with a rectifier 39. This rectifier is so connected that, when a master controller 18 is moved in the hoisting direction, the auxiliary series field winding is in circuit and acts accumulatively with the field winding 13. However, in power lowering, the rectifier 39 prevents energization of the winding 32, but if the load is such as to cause the hoist motor to regenerate, the rectifier allows the auxiliary series field winding to be excited accumulatively with the field winding 13. The motor is supplied from a generator G having a separately-excited field winding 15 adapted for variable and reversible excitation according to the position of the controller 18 so as to provide a plurality of hoisting and lowering speeds for the motor. The generator also has a series auxiliary field winding 31 which is included in circuit in the first and second hoisting positions of the controller and acts accumulatively with the field winding 15 under these circumstances. The field winding 31 is also included in circuit in the first lowering position of the controller when it is used accumulatively with the separately-excited field winding for power lowering and differentially for regenerative lowering. The generator auxiliary series field winding is excluded from circuit on all other operating points, the voltage output being controlled by regulating resistors 19-22 in circuit with winding 15. As shown, the field windings 31, 32 are connected across separate resistors 33, 38 in the loop circuit. In a modification, the auxiliary series field windings are connected across a common resistor by means of adjustable taps, Fig. 2 (not shown). The field winding 15 is connected across the armature of the generator in the " off " position of the controller so as to reduce circulating current in the loop circuit. Specification 644,573, [Group XXXVII], is referred to.