Patent GB-610343-A (GB)
Title: Improvements in or relating to electric generator-motor systems
IPC: H02P7/34
Filed: 1946-02-05
Abstract: 610,343. Automatic current control systems. IGRANIC ELECTRIC CO., Ltd. Feb. 5, 1946, No. 3621. Convention date, Feb. 5, 1945. [Class 38 (iv)] [Also in Group XXXVII] A generator-motor system comprises a generator having an armature and a field winding, supply means for energizing said field winding, means for initiating connection of said supply means to said field winding, a motor having an armature connected in circuit with said generator armature, means responsive to the motor-speed for controlling the maintenance of the supply means to the generator field winding independent of said connectioninitiating means, and controlling means comprising an electronic device responsive to and controlling the current circulating between said armatures to limit such current, said controlling means including means for predetermining the limit. A D.C. motor 11 is supplied from a generator 10, the field winding 10b of which is supplied from an A.C. source L3-L4 through a transformer 23 and gas-filled grid-controlled rectifying valves 24 and 25. At starting, the source L3-L4, a D.C. source L1-L2 and the motor field winding are energized and the generator armature is rotated by its prime mover. A resistor 31 affords means to adjust the phase-relation of the grid and anodepotentials of the valve 24 and 25. A switch 32 is moved downwardly for forward operation to energize relays 26 and 34. The anode of a high-vacuum triode valve 15 is connected to the cathodes of valves 24 and 25 and the movable contact of a voltage divider 16 is connected to the centre-tap of a phase-shift transformer 29. The winding 10b is connected to the secondary winding of the transformer 23 through the valves 24 and 25. At a predetermined motor armature voltage, a relay 33 closes to maintain the relay 26 energized when the switch 32 is returned to the " off " position. The grid-cathode potentials of a double-triode valve 14 are determined respectively by the algebraic sums of the potential-drops across the resistors 12 and 13 in the motor armature circuit, and that across the contact 22c of a voltage-divider 22 and the negative pole of the battery 21. As the motor armature current increases, the left-hand side of the valve 14 is gradually blocked and the current passed by the right-hand side increases to cause the valve 15 to pass a heavier current and reduce the potential of the anode 15b, so affecting the gridpotentials of the valves 24 and 25 that the current supplied to the generator field winding is reduced. The motor armature current is thereby kept at a substantially constant value as determined by the setting of the tap 22c. To stop the motor, the switch 32 is returned to the neutral position. The relay 33 remains energized, thus maintaining the relay 26. The relay 34 is de-energized to connect the tap of the divider 16 to the cathodes of the valves 24 and 25, and the anode 15b to the centre-tap of the transformer 29. The reversal of the motor armature current causes the left-hand side of the valve 14 to become conducting. An increase in braking-current causes an increase in the generator field current. The braking- current is kept at a substantially constant value as determined by the setting of the tap 22d. At low motor speed the relay 33 drops out to de-energize the relay 26 and disconnect the field winding 10b from the supply. Similar operation in reverse direction is afforded by moving the switch 32 to the upper position, the positions of the contacts 22b and 22a determining the motor armature current during acceleration and deceleration respectively. In a modification, the grid-cathodes circuits of the valve 14 additionally comprise a portion of a voltage divider which is connected across the motor armature. As the motor speed increases, the voltage-component derived from this voltage divider reduces the positive bias of the valve 14 to increase the current passed by the valves 24 and 25. The motor armature current is thereby kept at a low value at low speeds and increases rapidly with increasing motor speed.