Patent GB-299812-A (GB)
Title: Improvements in and relating to electric power systems for ship propulsion and otherpurposes
IPC: H02J9/08
Filed: 1928-11-01
Abstract: 299,812. British Thomson-Houston Co., Ltd., (Assignees of Kennedy, A.). Nov. 1, 1927, [Convention date]. Dynamos and motors combined for transmitting power; running generators in parallel; regulation, automatic.-An electric power system comprises a main generator, which may supply power to a main motor, such as a ship propelling motor, a load circuit for auxiliaries to which an auxiliary supply source is connected, and means for disconnecting the load circuit from the main generator under various conditions governed by the speed of a main generator. The object of the invention is to utilize a variable-speed main generator for supplying power to auxiliaries, so long as its output is suited to them, thus avoiding the use of a less efficient power source as long as possible. The auxiliary source is preferably a synchronous machine coupled to a normally idle turbine which is governed so as to take up load on a predetermined fall in speed; the field of this machine may be automatically varied to operate as a power factor improver when running light. The field of the main generator may be automatically controlled by a volts-per-cycle relay to maintain its excitation during speed variation at such a value as will ensure stable running of the auxiliary motors. A main turbine 1, controlled by a speed regulator 23 and a governor of the type shown in Specification 3026/13, [Class 57, Governors &c.], drives a synchronous generator 2 feeding a main motor 3. An auxiliary turbine 13 is coupled to and normally driven by a synchronous machine 12 connected to a load circuit 8 for auxiliaries and also connected to the main generator 2 through a switch 9. The machine 12 is connected to the load circuit 8 through a switch 17 which may be opened when it is desired to drive the auxiliaries from the main generator without operating the auxiliary unit, for example when handling cargo. The switch 9 is controlled by switches 25, 29, 30 and 27. The machine 12 is normally over excited, and when the switch 9 is opened a resistance in the field of the auxiliary machine 12 is inserted in its circuit to cause it to generate the voltage required. When the speed control lever 23 is moved to reduce the main generator speed to a predetermined value it opens the switch 25 and the auxiliaries become disconnected from the main generator, whereupon the governor 31 admits steam to the turbine 13 to supply power to the auxiliaries. Should the floating machine 12 fall in speed to a predetermined value the governor 31 likewise opens the steam supply and by a connection to switch 29 cause the switch 9 to open. The excitation of the generator 2 is manually con. trolled with the aid of a stability indicator such as is described in Specification 183,503. Should the ratio of supply voltage to frequency of the main generator reach a value, unsuited to the stable operation of the auxiliaries a relay 43 drops its contact 30 and causes the switch 9 to open. Further, to prevent the main motor 3 from being driven by the auxiliary unit, an overload relay 33 causes the switch 27 to open the connection between the motor 3 and machine 12 at switch 9. The circuit of the relay 43 has considerable reactance to cause it to hold its core up at a definite ratio of volts per cycle. When this value falls a contact 48 energizes a relay 49 which shunts the resistance 40 in the field circuit of the main generator. The excitation of this machine being suitably maintained by the vibratory action of the relays. Specification 283,902 also is referred to.