Patent GB-803945-A (GB)
Title: Improvements relating to engine-driven electric generating plant
Inventor: ATTOCK MARTIN OLDACRES
IPC: B60L15/00
Filed: 1954-12-15
Abstract: 803,945. Systems for transmitting mechanical power. ENGLISH ELECTRIC CO., Ltd. Dec. 15, 1955 [Dec. 15, 1954], No..36280/54. Class 38 (4). [Also in Group XXXVII] An engine-driven generator G, having a separately-excited field winding Gf; supplies traction motors M1, M2, the series field windings Mf 1, Mf2, of the motors each being provided with a reverser K. The field winding Mf 1 has diverter resistors DZ1, DZ3, affording two stages of field-weakening. The field winding Mf2 is similarly provided with diverters DZ2, DZ4. The generator field winding Gf is supplied from an exciter AG through a regulator LR which is operated by a pilot motor RM, and the regulator comprises a number of contact pillars 11 co-operating with spring-contact fingers 14 mounted on a metal ring 13. Several of the contact pillars are connected to a tapped resistor 12, the fingers associated with the pillars at positions LS1, LS2, acting as limit switches for short-circuiting the armature of the pilot motor at the end of travel of the regulator arm 15 in either direction. A roller 18 on the arm 15 engages the contact fingers 14 so as to operate them successively. The regulator also comprises normally open switches 19, 20, 21, adapted to be operated by cams 22, 23, 24, through tappets 25. The cams 22, 23 are driven from the cam 24 which is adjustably mounted on the regulator arm and has projecting dogs adapted to engage a pin on the cam 23. When the engine is under-loaded, the governor closes contacts GLS to energize relay VRR so that the pilot motor drives the regulator arm for reducing the resistance 12. If, during this operation, full-load conditions are obtained, the contacts GLS open and the armature of the regulator motor is short-circuited. When the engine is overloaded, the governor closes contacts GUS, and relay VLR is energized whereby the regulator arm is driven in the clockwise direction. Assuming that the arm 15 has progressed to the position affording maximum field excitation of the generator, and that the engine is still underloaded, the regulator arm will continue to move in the anticlockwise direction. The cams 22, 23 are now rotating solidly with the regulator arm so that, when the arm reaches the minimumresistance position, switch 19 is closed to energize relay VLR and reverse the pilot motor. The reversal of the regulator unloads the generator until the arm 15 reaches a position in which the cam 24 closes the switch 21, the cams 22, 23 having remained stationary during this backward movement so that the switch 19 remains closed. The closure of switch 21 energizes field-diverter contactors FDC1, FDC2, whereby resistors DZ1, DZ2 are connected in parallel with the respective motor field windings. Contacts FDCld complete a retaining circuit for the contactors FDC1, FDC2, and contacts FCD1a open to de-energize relay VLR and reestablish governor control of the pilot motor. The engine is still slightly under the full-load condition, so that the governor-operated contacts GLS are closed and relay VRR is energized for driving the regulator arm towards the minimum resistance position. If the engine is still under-loaded, the arm will continue to move until cam 23 closes switch 20, the switch 19 remaining closed. The relay VLR is again energized for reversing the regulator motor until switch 21 is re-actuated and a second stage of motor field-weakening is introduced by connecting the resistors DZ3, DZ4 in the field circuits. Governor control of the regulator motor is then re-established. Assuming that the traction motors are operating in the second stage of field-weakening and the generator is at maximum field, an extra demand for power causes the regulator arm to be driven in the clockwise direction. The arrangement is such that the second stage field-weakening contactors are opened, followed by the first stage contactors, whereby full excitation of the traction motors is re-established if the overload condition continues.