Patent GB-387368-A (GB)
Title: Improvements relating to power plants
IPC: H02P7/34
Filed: 1931-07-31
Abstract: 387,368. Electric systems for transmitting mechanical power. JUHLIN, G. A., Redscar, Moss Lane, Timperley, JOHNSON, E. M., 33, Poplar Grove, Brooklands, both in Cheshire, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. July 31, 1931, No. 21864. [Class 38 (iv).] Power plant particularly adapted for ship propulsion comprises a number of prime movers each driving an alternator, or an equivalent arrangement of two or more alternators, and a power shaft driven by a motor or a group of motors comprising stator windings equal in number to the prime movers, each winding being connected to one alternator or alternator equivalent only, and the said windings having no electrical or electromagnetic interconnection. Each prime mover has a governor which is responsive to and arranged to control the prime mover's speed under no load conditions and means are provided for joint control of the speed of the prime movers after their alternators have been synchronized and loaded. The system shown has three prime movers each driving an alternator adapted for reversible connection to a synchronous motor. The motors drive a common shaft. - Governors control the motive fluid admission to each prime mover and each is driven by an electric motor fed either by a generator on the prime mover shaft or, for joint control, by a generator 24 on the motor shaft, or by power supplied from auxiliary bus-bars 7 from which the field windings of all the dynamo-electric machines are supplied. Switches 18, 19, 20 are provided for individual control of alternator excitation, main circuit switching, and synchronizing respectively and controllers 15, 16, 17 are provided for joint control of plant in service, the first effecting power and speed changes, the second controlling direction and rotation of the power shaft and the third synchronization. For slow speed running prime movers 2a, 2c may be started, whereupon the generators 23 will drive the governor motors through switches 25 biassed to close their left-hand pair of contacts and the fluid admission will be adjusted to maintain constant no-load speed. Switches 18, 19, 20 are then closed and controller 16 closed in " ahead " position, resulting in energizing coils 13a, 13c to connect motors 4a, 4c to their alternators 3a, 3c. Controller 15 is now advanced to " slow " position whereupon the alternator field contactors are closed by segment 38, and simultaneously the governor motors are disconnected from the generators 23 and connected to generator 24 by segment 40 and by the operation of contactor coils 26 which are in parallel with the field contactor coils 10 ; the field of generator 24 is fully excited by segment 29. The synchronizing controller 17 is next moved through position a to position c, closing in turn motor field contactors 11a, 11c, contactor 11b being open circuited at switch 20b. The governor motors now regulate fluid admission to the prime movers to maintain a constant slow speed of the power shaft. To increase speed the controller 15 is advanced, so introducing resistance 34 in steps into the field of generator 24 and causing an appropriate adjustment of the action of the governor motors. To bring in an additional prime mover 2b it is first started, whereupon its generator 23 and governor motor 22 determine its no-load speed which may, however, be adjusted to equality with that of the running prime movers by a generator field rheostat 27. Closure of switch 19 will now energize the " ahead " contactor coil 13b, owing to the position of controller 16, and closure of switch 18 will close the alternator field contactor and change over the governor motor to the generator 24 for joint control. Closure of switch 20 will synchronize the generator 3b. To facilitate the synchronizing of an alternator the supply of fluid may be cut off from the prime mover before or during synchronization as by weakening at will, the fields of the governor motors. Correct sequence of switches 18, 19, 20 may be ensured by interlocks or suitable switch construction. Switches 28 are interlinked with switches 18 to ensure that the field conditions of the generators 23 requisite for idling speed control shall be established when a prime mover has been placed in service. Alternatively the rheostats 27 may be restored automatically by means of servomotors operated through auxiliary contacts associated with the switches 18. Interlocks between the controllers 15 and 17 may ensure that synchronization can only occur in suitable settings of the controller 15 or alternatively, an interlock may prevent the raising of the speed of the power shaft above a predetermined limit until the controller 17 has made its full travel. Where more than one power group is provided change over switches may be arranged to substitute an alternator of one group for an alternator of another group. The excitation of the generator 24 may be applied in the " off " position of the controller 15. The controller 15 may be arranged with but one synchronizing position in which all motors may be synchronized together. The transfer of governor control to the generator 24 may take place at the time of synchronization instead of when the alternators are excited. The operation of the system on reversing is described in the Specification. Additional contacts on the controller 16 may insert resistance in the field of generator 24 to permit increase of motive fluid to the prime movers when controller 15 is moved from " off " to " slow position and additional contacts on controller 17 may short-circuit this resistance when it is moved from its " off " position. Where the motors or alternators have polechanging windings and the speed of the prime movers requires limitation then the switches for pole-changing may vary the field circuit resistances associated with the governor control to effect such limitation. In a modified system not using the electrical system of governor control above described and forming the subjectmatter of Specification 388,089 each prime mover may have a long range centrifugal governor and a second motive fluid control, such as a throttle valve, and isolating valves operated from the controllers may be used to render either effective, the connections being electrical, mechanical, or hydraulic. Where over-excitation of the alternators during asynchronous running is required this will be applied by the contactors 8 and the reduction of the excitation will be effected through auxiliary contacts on the controller 17 after synchronization, for example by causing the fields to be connected to a half-voltage busbar. The invention may be applied in connection with any kind of prime mover.