Patent GB-394964-A (GB)
Title: Improvements in or relating to control systems for power plants comprising electric motors and prime movers
IPC: H02P9/06
Filed: 1931-12-03
Abstract: 394,964. Dynamo-electric machines aiding prime movers. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and COATES, H. J., c/o General Electric Co., Witton, Birmingham. Dec. 3, 1931, No. 33506. [Class 38 (iv).] Regulation, automatic.-In a system in which an electric motor 4 and a prime mover 3 jointly drive a variable-speed shaft 2 such as a propeller shaft in ship propulsion where the load increases with the speed of the shaft and is related to it, the outputs of the prime mover and electric motor are separately regulable and regulation of the motor output is automatically effected by means including a device 59 driven at the speed of the load so as to maintain the motor output, and hence the prime mover output, at suitable proportions of the load at different speeds thereof. The motor 4 is supplied from a generator 5 driven by an auxiliary engine 6 and having its excitation regulable by a resistance 15 actuated by a shaft 20 driven, through an electromagnetic clutch 19, by a reversible motor 18 which is selectively energized by a differential relay 54 one coil 55 of which is energized from a magneto-electric generator driven from the shaft 2 and the other 53 in accordance with the generator excitation through a variable resistance 27 regulated in step with resistance 15 by the shaft 20. The prime mover, e.g. a Diesel engine, is controlled by air, fuel, &c. levers 7, 8, 9 and a reversing wheel 10 which reverses its cams and also reverses the excitation of the generator 5. The motor 4 is used also to start the main engine and is controlled by a threeposition lever 79 biased to a middle neutral position. The wheel 10 prepares, through contacts 11, 12, 13, circuits for either the "forward" or the "astern" contactor 35, 44 respectively which circuits are completed through interlock contacts 38, 47 thereon to D.C. mains 62, 63 during starting by connection of contacts 85, 86 when the lever 79 is placed in the " start '' position 80. These contacts 85, 86 also energize a coil 65 of a main contactor 66 which closes and energizes bus-bars 61 which supply the field of the motor 4 and, through whichever contactor 35, 44 is closed, the generator field 14 through the resistance 15. In the starting position 80 contacts 86, 87 also close and energize a contactor 88 which cuts out part of the resistance 15 and causes the generator voltage to build up rapidly. Rotation of the shaft 2 now causes unbalance of the relay 54 which operates to energize the reversible motor 18 and clutch 19 through drum contacts 29 to increase the excitation of the generator 5 and of the balancing coil 53 as the shaft 2 speeds up. During starting the output of the motor 4 is limited by an overpower relay 74 which functions to stop the motor 18. When the engine 3 fires, the lever 79 is returned to its " neutral " position. The circuit of the contactor 88 is now broken, the circuit of the contactor 35, 44 is maintained through an economy resistance 43, 52 by drum contacts 30 on the shaft 20 which are closed due to rotation thereof and the circuit for the contact 57 of the relay 54 giving reversal of the motor 18 is completed by drum contacts 28. The circuit of coil 65 of the main contactor 64 is maintained through an economy resistance 71, an emergency push-button 89 and an overcurrent relay contact 78 directly across the mains 62, 63. Interlock contacts 47, 38 on contactors 44, 25 prevent closure of one contactor whilst the other is closed. The system now functions so that the field of the generator is regulated to maintain balance of the relay 54. The motor may be stopped (1) by switching off the engine 3, the generator excitation then following the shaft speed down to zero, (2) by moving the lever 79 to the " stop " position 81 when the coil 55 is de-energized, contacts 83 and segment 82 being disconnected and the generator excitation is gradually reduced to zero, (3) by opening the emergency switch 89 to open the contactor 64, and (4) automatically, by the relay 78 if the motor current becomes excessive. Discharge resistances 60, 73 are connected across the field windings when contactors 64, 35, 44 are open. In a modification, the regulator controlling the generator field may be operated directly by a member driven at a speed proportional to the shaft speed and associated by means of a slipping coupling, e.g. an eddy current clutch, with a second member biased, e.g. by a spring, to a predetermined position, so that the torque on the second member is proportional to the speed of the first member and opposes the biasing force which increases with displacement of the second member whose equilibrium positions correspond to specific shaft speeds.