Patent GB-857486-A (GB)
Title: Improved electric drive control system
IPC: H02P7/34
Filed: 1959-06-01
Abstract: 857,486. Control of D.C. motors; controllers. ALLIS-CHALMERS MANUFACTURING CO. June 1, 1959 [June 2, 1958], No. 18685/59. Class 38 (3). [Also in Group XXXV] Electric motors are adapted to be supplied from a Ward-Leonard generator as well as from a rectifier which is fed through a transformer having a tap-changer. The control of the tapchanger is inter-related with that of the generator and means are provided to prevent operation of the tap-changer when the motor current exceeds a predetermined value. As shown, when a circuit-breaker 26 is in the open position a motor 1 is supplied from generator 5 and motor 15 from rectifier 20. Depression of push-button 66 causes pilot motor 62 to adjust potentiometer 53 and increase the excitation of control winding 50 of magnetic amplifier 34 whereby the voltage of the generator is increased. The magnetic amplifier supplies a field winding 11 of the generator and has a bias winding 45 and a voltage-responsive winding 49 in opposition to the control winding 50. Further increase in generator voltage is obtained by depressing push-button 79 to energize pilot motor 74 which drives rheostat 51 in series with the winding 50. Actuation of push-button 200, in circuit with the closing-coil 149 of circuitbreaker 94, closes contacts 96 so that transformer 90 is energized to supply the rectifier 20, the voltage applied to the rectifier being dependent upon the position of selector switch 84 on the shaft of the pilot motor 74. The rectifier is further controlled by a phase-shifter 110 driven by pilot motor 115, the output of the rectifier being increased by actuating pushbutton 120. A reactive phase-shifter 127 maintains the rectifier-output at a desired level since a control winding 135 is energized in accordance with the voltage across motor 15, and a reference winding 141 is energized by a portion of the generator voltage appearing across potentiometer 82 and resistor 85. In this manner, the rectifier voltage is varied in response to variations in the generator voltage caused by load changes. A resistor 136 in series with the winding 135 is automatically calibrated to compensate for changes in the position of tapchanger 98. Operation of the tap-changer while the motors are operating on separate supplies may be effected by push-buttons 163, 164, in circuit with a pilot motor 105, provided that contact 205 is closed and the phase-shifter 110 is at the position for minimum rectifier voltage. Both motors may be fed in common from the generator and rectifier by closing the circuit-breaker 26, the circuit-breaker 94 being open and the tap-changer at its position for lowest output voltage. The generator voltage is increased by closing push-button 66 until the maximum position of potentiometer 53 is reached and contacts 150 are closed to energize the closing coil 149 of circuit-breaker 94. Closure of contacts 125 allows the motor 115 to drive the phase-shifter 110 towards the maximum output position of the rectifier. Loadsharing between the generator and rectifier is provided by winding 143 of the reactive phaseshifter 127 which is energized in accordance with the difference between the output currents of the generator and rectifier. Under these conditions, the windings 135 and 141 are inoperative. Actuation of push-button 79 increases the generator voltage and changes the positions of selector switch 84 to open relay C1 and close relay B1, whereby the motor 74 is stopped to prevent further increase of voltage. When the relay B1 picks up, a relay 192 is energized to trip the circuit-breaker 94 and operate the tapchanger motor 105 in a direction to move the tap-changing mechanism from tap 101 to tap 100. At the same time that this tap is engaged, contact 169 engages contact 171 whereby relay B2 picks up and de-energizes relay 192 to stop the motor 105 and re-close the circuit-breaker 94. Further increase of voltage is obtained by re-actuating push-button 79 until the selector 84 engages segment 168 and initiates another tap-change. Load relays 189, 190, prevent operation of the tap-changer motor under excess current conditions. Relays A2, B2 and C2 are of the time-delay type to prevent the tapchanger from stopping between taps.