GB510336A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

510,336. Master control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 31, 1938, No. 3036. Convention date, Jan. 30, 1937. [Class 38 (iii)] Field and armature control. -A number of resistances 18, 19, in the armature circuit of a hoist motor 10 are shunted in succession by contactors 27, 28 operating in sequence, and the contactor 28 operated last in the sequence is controlled by a relay 32 having a coil connected in series with a rectifier 33 across one or more of the resistances 18, 19, so that this contactor 28 is prevented by the relay 32 from operating to shunt the last resistance 19 when the motor 10 is motoring in the lowering direction, but is allowed to operate when the motor is motoring in the hoisting direction or is overhauled in the lowering direction. Upon movement of a master controller 15 to its first lowering position contactors 45 and 50 are energised, the former opening a closed braking circuit across the motor 10 and the latter energising a contactor 17 which connects the motor to the source in the lowering direction, the motor field 13 which is normally a series field being connected for lowering as a shunt winding. The motor armature and field circuits include a resistance 20 while its field circuit also includes a resistance 29. By further movement of the controller 15 contactors 28 and 27 are de-energised in sequence, and open to insert further resistances 19 and 18 in the armature circuit, and contractors 26 and 25 open to insert resistances 23 and 22 in the field circuit. The operation of the contractor 25 energises a contactor 30 which operates to connect the resistance 29 in parallel with the resistance 20, and the field circuit across the supply in circuit with the resistances 22, 23, only. A relay 31 is connected across the motor by operation of the contactor 30, and when the motor speed is high enough, this relay 31 energises the contactor 27 to shunt the armature resistance 18. The contactor 27 is interlocked with a contactor 24 which then opens with a time delay to insert a resistance 21 in the field circuit. The contactor 28 is also interlocked with the contactor 27 but is energised to shunt the resistance 19 only when the normally closed contacts of a relay 32 are closed. This relay 32 is energised from the resistances 18, 19, in series with a rectifier 33 and is therefore energised to open its contacts and prevent energisation of the contactor 28 unless the motor is overhauled. In this case the motor current reverses, the rectifier 33 prevents energisation of the relay 32, and this relay 32 closes its contacts to cause the contactor 28 to operate following operation of the contactor 27, thus the resistance 19 is shunted. Acceleration of the motor in the hoisting direction is similarly effected by movement of the controller 15 from its off position in the opposite direction. The motor current is then in such a direction that the relay 32 is not energised, and therefore the contactor 28 can be energised in the final position of the controller to shunt the resistance 19.