Patent GB-619848-A (GB)
Title: Improvements in excitation control of dynamo-electric machines
IPC: H02P7/34
Filed: 1944-07-28
Abstract: 619,848. Exciting dynamos; automatic control systems. BRITISH THOMSON-HOUSTON CO., Ltd. July 28, 1944, No. 14419. Convention date, July 28, 1943. [Classes 35 and 38 (iv)] [Also in Group XXXVII] An excitation control system for a dynamoelectric machine, wherein a field winding of the machine is energized by a second dynamoelectric machine, comprises means for applying to a voltage control field winding of the second dynamo-electric machine the difference between a voltage derived from the armature voltage of the first dynamo-electric machine and a reference voltage, which is preferably adjustable, so as to force or reduce the excitation of the first dynamo-electric machine when the voltage derived from the armature of the said machine is less than, or higher than, the reference voltage. The armature of an electric motor 10 is supplied from a main generator 12, the separately-excited field winding 12a of which is energized by an armature-reaction excited dynamo-electric machine 15. The machine 15 has a field winding 15c, which is excited from a source of constant potential, and a field winding 15d which is excited with a potential which is the difference of a voltage derived from the generator 12 and the voltage of a pilot generator 19. The generator 19 comprises a field winding 19a which is supplied from a constant source through a plurality of resistors which are progressively short-circuited by movement of a master switch 11. For forward rotation of the main motor, the master switch is moved to energize a relay 17, thereby exciting the fields 15c and 19a. Initially the voltage of the pilot generator 19 exceeds that, derived from the generator 12, across a resistor 24b, and a current is driven through a resistor 25, the resistor 24b, and the filed 15d, so that the field 15d is energised accumulatively, with the field 15c to force the excitation of the main generator. Shortcircuiting of the resistor 25 is prevented by a rectifier 27. Should the voltage of the generator 12 exceed that determined by the pilot generator, a current will flow from the positive terminal of the resistor 24b through a contact 17a of the relay 17, the armature 19, and the field 15d in the opposite direction to that previously obtaining. The voltage of the main generator, and the speed of the motor 10, are therefore regulated to values determined by the reference voltage of the pilot generator. Different values are obtained by short-circuiting the resistors in series with the field 19a. To prevent over-shooting of the main generator voltage, an auxiliary field 19b of the generator 19, which acts differentially to the field 19a, is excited from the secondary winding of a transformer 29, the primary of which is supplied from the main generator. Reverse action of the main motor is provided by the movement of the main switch 11 to close a relay 18. During the forcing-action of the main generator field, current will flow through a resistor 26 to the field winding 15d, and a rectifier 28 will prevent short-circuiting. In other respects operation in the reverse direction is similar to that described.