| 摘要 |
719,654. Control of A.C. motors. GENERAL ELECTRIC CO., Ltd., and FRIEDLANDER, E. S. April 9, 1953 [April 9, 1952], No. 9095/52. Class 38(3) A traction system comprises a synchronous motor 15 which also acts as a phase converter and drives a variable speed frequency converter machine 21 having windings supplied with three phase current from the machine 15 and other windings arranged to supply traction motors 25. The traction motors may be of the squirrel cage induction type and are adapted for pole-changing. The motor 15 may drive the frequency changer 21 directly or through an electrical transmission comprising a Ward Leonard generator 16 and motor 20, the generator having a boosting or bucking exciter 50 controlled by a reversing potentiometer 30, 31. An auxiliary frequency converter machine 70 is mechanically coupled to one of the traction motors and has stator windings fed from the supply to these motors. The machine 70 is shown as connected to a pole changing switch 90 so that the number of poles of the machines 25 and 70 are changed simultaneously. The output of the auxiliary frequency converter, which is dependent upon the slip of the traction motor, is applied to a hysteresis motor 71 driving a direct-current tachometer generator 72. A field winding 52 of the exciter 50 is connected to the generator 72 and exerts a modifying influence on the excitation of the direct-current generator 16 tending to reduce the slip of the traction motors. The output of the tachometer generator 72 is also applied to a safety device 91 which may consist of a relay arrangement permitting the traction motors to be connected to the frequency converter only when the output of the tachometer generator is small. In this manner, the traction motors are not energized unless the output frequency of the machine 21 corresponds closely with the speed of the traction motors. The auxiliary frequency converter 70 may be replaced by a number of separate machines of fixed pole numbers, an appropriate auxiliary machine being selected according to the number of poles for which the traction motors are connected. Specification 719,652 is referred to. |
