Patent GB-988729-A (GB)
Title: Motor control system and magnetic amplifier therefor
IPC: B66C13/26
Filed: 1962-09-05
Abstract: 988,729. Automatic speed control. SQUARE D CO. Sept. 5, 1962 [Sept. 25, 1961], No. 33976/62. Heading G3R.[Also in Divisions H2 and H3] In a motor control system using auto-selfexcited transductors, each transductor 10, Fig. 1, has a controlling voltage from a rectifier 44 applied to terminals 35,38 intermediate the main windings 18, 19 and associated power rectifiers 24, 25 and includes biasing circuits which crossconnect the terminals with taps 36,39 on the main windings, the biasing circuits each comprising a resistor 30,31 and a rectifier 28,29 functioning to maintain the transductor in the unsaturated "off" condition in the absence of a controlling voltage. The control system is shown in Fig. 6 in which a polyphase induction hoist motor 60 has resistance-loaded secondary windings 60s and primary windings 60p connected through transductors 1L, 2L, 1H, 2H and C to power supply lines L1, L2, L3. Controlling voltages for the transductors are applied from rectifiers 44, the transductors 1L, 2L and C or 1H, 2H and C becoming conductive so as to cause the motor to lower or hoist, depending on whether a transformer 70 or 71 is energized through respective controlled rectifiers 76 and 78. These controlled rectifiers are responsive to outputs from "lower" and "hoist" firing units 79,80, one unit being operated by a negative input and the other by a positive input. Both firing units have their inputs connected in series with (a) a potential developed across resistor 86 of value and polarity determined by the position of a vane 83a in a movable core transformer 83, and (b) the potential developed across resistors 98 and 99 by a tacho-generator 82,the outputs from transformer 83 being rectified at 84 and 85. Operation is initiated by displacing the vane 83a in the required direction H (hoist) or L (lower) so that off-normal contacts 81c are closed and normally closed contacts 81b opened. An appropriate hoist or lower potential is obtained across resistor 86 which operates the appropriate firing unit and causes controlling voltage to be applied to the hoist or lower transductors. An undervoltage relay 88 is continuously operated, and closure of off-normal contacts 81c causes a brake relay 65 and a slow-operating and slow-releasing timing relay 89 to be energized. The timing relay 89 pulls up the main contactor 62 to switch through the power supply L1-L3 to the motor, and the brake relay permits a solenoid 63 to release a spring friction brake when the supply is switched through. The motor speed is controlled by the net difference potential across resistors 86,98 and 99 as developed by the displaced vane and the tacho-generator, the speed being limited to a value determined by the vane displacement by alternate operation of the two firing units as the net difference potential fluctuates between positive and negative values. When the vane is moved to the central (off) position, the delayed release of the contactor 62 by slow-release relay 89 ensures that power is applied to the motor until the drive comes to rest. The movable core transformer 83 also controls off-normal contacts 81a which are opened only when the vane is displaced to its extreme lowering position. These contacts are included in the hoist section of the transformer and when opened raise the potential across resistor 86 so that an overhauling load is lowered under regenerative control. The motor may be energized when the vane is in the off position by operating push button 90. All the control windings of the transductors have a small premagnetizing current which is determined by resistors 78<SP>1</SP>, 76<SP>1</SP> in parallel with the controlled rectifiers.