GB281863A - Improvements in and connected with the starting of motor converters - Google Patents

Abstract

281,863. English Electric Co., Dtd., and Schroeder, G. Nov. 30, 1926. Rotary transformers; field magnets, dampers on poles of. - In an arrangement for starting motor converters by producing a reduced flux in the alternating-current element of the converter, the pole-faces of the continuous-current element are provided with a winding or windings capable of acting during starting as the polyphase secondary coils of an induction motor. These may take the form of a squirrel cage which gives a high effective resistance at starting and serves as a damping winding after synchronizing. Fig. 1 shows windings 1, 3 which give a 2-phase effect in producing torque, the winding 1 serving as a compensating winding during normal running and being wound in the usual manner symmetrically with respect to the mid-polar axes and in series with the commutating-pole coils 2. The other winding 3 is symmetrical about the polar axes and is preferably in the same slots as the winding 1. As shown in Fig. 2, the windings 2, 3 form a 2-phase group connected through resistances 4, 5, preferably liquid, to the neutral point 7 and the negative bus-bar 6. The point 7 is also connected to the other end of the winding 3. The continuous-current armature of the converter is connected to the positive bus-bar 11 through a switch 10, and the field circuit 8, 9 is completed in the usual manner. For starting, the stator flux is reduced in the alternating-current element of the machine, the switch 10 is open, a switch 12 in series with the winding 3 closed and the resistances 4, 5 are inserted at full value. The resistances 4, 5 are then reduced and when normal speed is approached they are short-circuited, the stator flux is increased and the machine pulls into step. The switch 10 may then be closed and the switch 12 opened to convert the winding 3 into a damper. Thereafter, the windings 1, 2 act normally for commutating and compensating. The windings 1 and 3 may form a double squirrel cage with magnetic leakage between them or they may be wound in narrow deep slots or other means may be used to give a high effective resistance at starting. Also the commutator brushes may be lifted during starting.