GB529577A - Improvements in and relating to electric regulating systems - Google Patents

Abstract

529,577. Automatic control systems for dynamo - electric machines; converting. BRITISH THOMSON-HOUSTON CO., Ltd. March 16, 1939, No. 8447. Convention date, March 17, 1938. [Classes 38 (ii) and 38 (iv)] Voltage.-The field winding 3 of a synchronous machine 1 is supplied with D.C. from an A.C. circuit 15, to which the main winding 2 of the machine is also connected, through a rectifier comprising a transformer 14 and immersion-igniter valves 9-13. Control impulses for these valves are obtained from grid controlled valves 30 which receive lagging alternating control potentials from a transformer 41, the moment of ignition being determined by means of a variable-negative D.C. bias introduced in the circuit between the neutral point connections of the windings 43, 44 and the cathodes of the valves 9-13. This includes a constant bias across a resistance 79 supplied by a rectifier 75, and a bias across a resistance 48, supplied by a rectifier circuit 45, which varies in dependence on the potential of the circuit 15 and effects regulation of the main rectifier to adjust the potential of the machine 1 to constancy. An overriding control is provided by a bias across the resistance 86, which gives the machine 1 a drooping characteristic after a predetermined load has been reached. This is effected by means of an arrangement 80, comprising rectifiers 82-84 supplied from current transformers 81, which produces a potential proportional to the load current, which is applied, in opposition to a constant potential across a tapped portion of a resistance 88, to the resistance 86. To prevent the current through the winding 3 being reduced below a predetermined value, a circuit 103 is provided comprising valves 105 connected to shunt the resistances 48, 79 and 86 through a resistance 49 and which become conductive in response to a predetermined minimum voltage across the winding 3 to limit the amount of negative bias across these resistances. In the event of a sudden reduction of current the energy in the windings 3 discharges through the valves 8-13 which temporarily act as an inverter. An overriding biassing circuit 100 for limiting the maximum current through the field windings 3 is provided and is operated by a relay 94 in response to overload. A further overriding biassing circuit completed by a press button switch 116 is provided for use during starting. The valves 60 in the circuit 45 and the valves 105 in the circuit 103 are duplicated to avoid failure.