Patent GB-513114-A (GB)
Title: Improvements in and relating to electric motor control systems
IPC: H02P5/685
Filed: 1938-03-17
Abstract: 513,114. Master control of D.C. motors; controllers. BRITISH THOMSON-HOUSTON CO., Ltd. March 17, 1938, No. 8297. Convention date, March 17, 1937. [Class 38 (iii)] With combinations of resistances, field and armature control; dynamo-electric braking. With an accelerating master controller 28 and a braking master controller 29 in their off positions closure of a control switch 152 energizes a braking switch 34 and a field controlling contactor 149 to establish coacting connections for the motors 10, 11, and 13, as shown in Fig. 7. Simultaneously a coil 71 is energized to operate valves 69 and 70 of a fluid actuating device 24 for a controller 25, 26. The part 25 of this controller may be as described in Specification 456,123. Thus pressure is applied to a chamber 73 but movement of the controller 25, 26, is prevented by the energization of a coil 84 which closes a valve 77 in a passage connecting an operating piston 66 with the chamber 73. Upon operation of the controller 28 to a switching position, the switch 34 and the contactor 149 are opened and line circuit-breakers 30, 31, are closed. Thus the motors 10-13 are connected to the supply in series with resistances 18, 19, 20 and with their fields 14-17 shunted by reaclances 55, 57. The field shunting circuits include resistances 54, 56 controlled by a fluid pressure actuated diaphragm 42 operating contacts 50, 51, and when the circuit-breaker 31 closes, the operating coil of a valve 45 is energized to effect operation of the contacts 50, 51, to insert the resistances 54, 56, in the field shunting circuits. The controller 28, when operated to a running position, energizes a contactor 38 to exclude the resistance 20 from the motor circuit, and the device 24 operates the controller 25 from a position A to a position B progressively to remove the resistance 18 from the motor circuit. A coil 84 is at this time energized and is effective to permit the valve 77 to open so that the controller is moved at high speed. The coil 84 is controlled by an accelerating relay 27 having a coil 110 carrying the motor current and is effective to slow the controller down if the motor current exceeds a predetermined value. Upon a further increase of motor current the relay 27 energizes a coil 83 and the valve 77 is closed to stop movement of the controller. The relay 27 is provided with a shunt coil 111 opposing the coil 110 and effective to cause de-energization of the coil 83 immediately after it is energized. Thus the controller 25 moves very slowly at a speed dependent on the time the contacts of the relay 27 remain closed. Movement of the controller 28 to further running positions is effective to adjust a spring 28 biassing the relay 27. When the controller 25 reaches its position B and the resistance 18 has been excluded from circuit a switch 39 is operated through contacts 85 on the controller 26, to exclude the resistance 19 from circuit and reinclude the resistance 18. The operation of the switch 39 de-energizes the valve coil 71 to operate the valves 69 and 70 and effect return of the controller 25 to its initial position A. Thus the resistance 18 is again excluded gradually from the circuit. When the position A is reached contacts 88 on the controller 26 effect de-energization of the coil of the valve 45 and a spring 44 operates the contacts 50, 51, upwardly progressively to shunt the. motor fields. The speed at which the contacts 50, 51, operate is controlled by the relay 27 in a manner similar to that in which the speed of operation of the controller 25 is controlled; the relay 27 controlling a coil operating a valve 58. In order to introduce braking the controller 28 is operated to its " off " position, the circuit-breakers 30, 31, and the contactors 38, 39 being opened and the contactors 34 and 149 closed. The motors are thus connected as shown in Fig. 7, but the shunting of the field windings prevents any generator action, and to effect braking the controller 29 is operated to a service position whereupon the operating coil of the valve 45 is energized and the field shunt circuits opened. The operation of the controller 29 also de-energizes the coil 83 and the controllers 25, 26 are operated to their positions B, the resistance 18 being progressively removed from circuit at a rate controlled by the relay 27, the coil 109 of which is in the braking circuit. When the position 13 is attained the switch 39 is operated to reinsert the resistance 18 and eliminate the resistance 19. The operation of the switch 34 prepares a circuit for the contactor 38 which is completed when the contactor 39 operates but the contactor 39 in operating locks the contactor 38 open. The controller 25 is then returned to its position A to progressively cut out the resistance 18 and when the position A is attained the switch 39 is deenergized to reinsert the resistances 18, 19. This operation of the switch 39 releases the contactor 38 which operates to cut-out resistance 20. The controller 25 is then operated to its position B to exclude the resistance 18 a third time whereupon the switch 39 is operated again to reinsert the resistance 18 and eliminate the resistance 19. The controller 25 then returns to its position A progressively to cut out the resistance 18 for a fourth time and give the final braking circuit. A relay 40 is provided which functions to predetermine the amount of resistance in the braking circuit during coasting before operation of the braking controller. A coil 100 is connected across the fields 14, 15 and positions a cam 94 in accordance with the motor speed. This cam co-operates with a winding 103 to control a contact 92, a conducting finger 98 and a latch 102. Upon operation of the controller 28 to its switching position the coil 100 is energized, and in the running position of the controller 28 the coil 103 is energized to release the cam 94 for movement in accordance with the energization of the coil 100. The initial energization of the coil 100 moves the cam 94 to the extreme right hand position where it is maintained during the accelerating operation. When the field shunting circuits are completed the cam 94 begins to move towards its left hand position. It takes up a position corresponding to the motor speed when braking it to be initiated, and upon operation of the controller 28 to its off position it is latched in this position. The stop coil 83 is de-energized and the controller 25 is operated until contacts 91, 92, reclose to re-energize the coil 83. Thus the resistance 18 is eliminated to an extent depending on the coasting speed so that the braking action starts immediately the controller 29 is operated to its service position. If the coasting speed is so low that braking is to set in with the resistances 19 or 20, eliminated contacts 98, 97, 96, are effective to perform this control. An additional winding 255 on the relay 40 is effective to release the latch 102 when the flow of braking current is appreciable so that the controller 29 may be operated to its off position to de-energize the coil of the valve 45 and terminate the braking at any stage, the cam 94 being moved to its left hand position to close contacts 91, 92, and the re-establishment of the braking control being effected by returning the controller 29 to a service position. The operation of the controller 29 to its off position the coil 83 is energized and the controller 25 held in its particular position until braking is resumed. Reference has been directed by the Comptroller to Specifications 458,390 and 459,640.