GB656158A - Improvements in and relating to control systems for electric motors - Google Patents

Abstract

656,158. Control of several A.C. motors. IGRANIC ELECTRIC CO., Ltd., and WEST R. A. May 28, 1948, No. 14487. [Class 38(iii)] A system of electric motors which drive a travelling structure which runs on two rails and has independent motors for the driving wheels of the two rails comprises four polyphase induction motors, two for driving the wheels of one rail and two for driving the wheels of the other rail, wherein two of the motors appertaining to different rails are connected together and supplied so that their rotors move in synchronism, and the other two motors are connected in cascade with the first two motors. A travelling structure which runs on two rails has four independent polyphase induction motors for the driving wheels of the structure, motors 8 and 9 appertaining to one rail and motors 10 and 11 to the other. The stator windings 12 and 13 of the leading motors 8 and 10 are connected in parallel to three-phase supplylines through reversing contactors 17 and 18, the rotor winding 19 of the motor 8 is connected to the rotor winding 20 of the motor 9, and the rotor windings 24 and.25 of the motors 10 and 11 are similarly interconnected. The rotor circuits of the motors 8 and 10 are joined by synchronizing connections 29, 30, 31 which pass current from one motor to another if the motors fall out of synchronism in such manner as to restore the motor speeds to equality. The stator windings 32, 33 of the motors 9, 11, are interconnected, a regulable resistance 34 being provided for controlling the four motors. The cascade connection, and the mechanical coupling through the rails, of the motors 8, 9, and 10, 11, provides a synchronous speed of half that of a single independent motor, which is a suitable condition for obtaining a heavy synchronizing torque between the two sets of motors. A switch 35 disconnects the motors 10 and 11 from the mains when it is desired to correct mis-alignment. This switch has contacts in the stator circuit of the motor 10 and in the leads 29, 30. During coasting the stator windings 12 and 13 remain connected to the mains, maximum resistance being placed in circuit with stator windings 32, 33 which are virtually on open circuit. A heavy synchonizing current flows through conductors 29, 30 and 31. In a modification. Fig. 4 (not shown), the stator windings 32, 33 have separate control resistors.