Patent GB-642337-A (GB)
Title: Improvements in or relating to direct current motor control systems
IPC: H02P7/34
Filed: 1948-01-29
Abstract: 642,337. Exciting dynamo-electric machines. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Jan. 29, 1948, No. 2694. Convention date, Feb. 21, 1947. [Class 35] [Also in Group XXXVII] In a control system for a direct-current dynamo-electric machine the field excitation of which is controlled by a regulating generator having a variably excited pattern field winding, the regulating generator is provided with a modifying field,winding which is connected for energization in opposition to the pattern field winding in accordance with a differential between the voltage of the regulating generator and a voltage from the dynamo-electric machine during a transition period following an adjustment of the excitation of the pattern field winding. A reversible D.C. motor 12 is supplied from a variable voltage generator 13 and has a main field winding 15, a currentlimiting field winding 16, and a compensating field winding 17. The generator is provided with a compensating winding 19 and a main field winding 20 which is energized from an exciter 22 having a winding 25 excited from a regulator generator 27. A pattern. field winding 32 of the regulator generator is connected to a  supply-source through resistors 34, 35 and 36 by reversing relays 38 and 39 which are under the control of a drum switch 43. The generator 27 has a differential field winding 31, energized in accordance with the voltage of the generator 13 and opposing the winding 32, a self-exciting winding 30, and an anti-hunting winding 29 which normally opposes winding 30. The field winding 15 is energized from an exciter 45 having a forcing winding 47 fed by regulating generator 50. A pattern field winding 52 of this regulating generator is energized from a supplysource through resistors 57, 58 and 59 which are controlled by drum switch 43. The generator 50 has a differential field winding 53, energized in accordance with the voltage of the exciter 45 and opposing winding 52, and an anti-hunting winding 54. The armature current of the motor 12 is limited by means of a generator 60 having a field winding 62 connected across winding 17 to be energized in accordance with the motor armature current. A control resistor 66 is .provided. The generator 60 has a shortcircuited field winding 64 and its characteristic is such that the output voltage is substantially zero until the excitation of the winding 62 reaches a pre-determined value, whereupon the output voltage rises rapidly. The generator 60 is connected to the motor field winding 16 and a field winding 55 of the regulating generator 50 by means of reversing relays 67 and 68 which are controlled by the switch 43. In order to limit the armature current of the motor 12 during regeneration, when the main field winding 15 is strengthened, a modifying field winding 56 of the regulating generator 50 is energized under this condition to oppose the pattern field winding 52. The winding 56 is energized in accordance with the difference of the output voltage of the generator 50 and a portion of the voltage of the generator 45 as selected from a voltage divider 73. A rectifier 75 prevents energization of the winding 56 when the master switch is operated to reduce the excitation of the field winding 15. A relay 82 is energized through contacts of a relay 78 and prevents too sudden reduction of the output voltage of the generator 13 when increase of the excitation of the field winding 15 lags behind the movement of the master switch 43 towards the reverse position. A relay 85 is responsive to the voltage of the generator 13 to shunt resistors 58 and 59 and produce a strong motor field when the generator voltage is below a predetermined value. When the switch 43 is moved. in a forward direction, relays 38 and 67 close. The output of exciter 45 is initially at a maximum, the resistors 58 and 59 being shunted by segment 43c.. The voltage of the generator 13 is initially at a minimum value, resistors 34, 35 and 36 being connected in series with the field winding 32. Movement of the controller successively removes resistors 36 and 35, and further movement inserts resistors 58 and 59. If the controller is rapidly reversed to remove resistors 58 and 59 the motor armature current tends to reverse and reach a high value due to re-generation. The voltage of the exciter 50 increases before that of the exciter 45, which it controls, and the field winding 56 is energized to oppose the winding 52 so reducing the rate of increase of the voltage of the generator 50 and the excitation of the winding 15. The rectifier 75 may be dispensed with.