Patent GB-395743-A (GB)
Title: Improvements relating to electric regulating systems for dynamo electric machines
IPC: H02P9/26
Filed: 1932-01-12
Abstract: 395,743. Automatic. regulation. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.- (General Electric Co. ; Schenectady, New York, U.S.A.) Jan. 12, 1932, No. 928. [Class 38 (iv).] Relates to the regulation of an A.C. machine 1 in which the field winding 5 of an exciter is supplied from a grid-controlled rectifier provided with means responsive to voltage change for adjusting the grid control, and consists in providing means which, on the occurrence of a sudden change of load on the machine, modifying the grid control to compensate for variations in the machine voltage due to armature reaction. The field 5 of the exciter can be connected by means of a switch 7 either to the armature 4 so that the exciter acts as a selfexcited generator for starting purposes or to a rectifier comprising three valves 17, 18, 19 supplied from the 3-phase line 2 through a transformer 20 having zig-zag windings to prevent direct current saturation. The valves 17, 18, 19 are controlled by applying to each grid a voltage composed of an A.C. voltage 90‹ out of phase with the anode voltage superimposed on a D.C. bias produced by current flow through a resistance 32. A three-phase transformer 37 fed from the line 2 through resistances 42. has three secondaries 43 feeding three full-wave rectifiers 38, 39, 40 the outputs from which are connected in series and across one diagonal of a bridge having one pair of opposed sides formed by resistances having linear voltage-current characteristics and the other pair of sides formed by resistances 35, 36 having non-linear voltage-current characteristics so that when the impressed voltage across the diagonal 44, 45 exceeds or falls below a predetermined voltage a voltage is produced across the 'other diagonal. This voltage is impressed on the grid of a valve 47 and controls the anode current flowing and therefore the voltage across the resistance 32. To prevent hunting due to armature reaction and time delay in the exciter a resistance 56 in the grid circuit of valve 47 is connected through a condenser 57 across the exciter. As the exciter voltage changes the transient charging or discharging current of the condenser 57 causes a bias to be applied to the grid opposing the change. As a resistance condenser combination 58, 59- in the circuit from bridge to grid delays application of full change of voltage, the delay may be adjusted by varying the resistance. To compensate for line drop the secondary of a current transformer 64 in one of phase lines is connected to adjustable tappings on an inductance 63 and resistance 62 in one of the leads to the transformer 37 so that a voltage is injected into the control circuit proportional to and in phase with the voltage drop in line. When two or more synchronous generators are run in parallel to ensure that each takes its share of wattless current a current transformer 65 is provided, the secondary of which is connected to an adjustable inductance 66 so that the voltage injected into that lead in phase with the voltage therein is proportional to the wattless current flowing. To maintain the current substantially constant above a predetermined load current a current transformer 67 supplies a full-wave rectifier 70 which is connected in parallel with the rectifier 38, 39, 40 supplying the bridge. When the output voltage of the rectifier 70 exceeds that of the series rectifiers 38, 39, 40 it assumes control of the bridge to maintain substantially constant current control. In a modification the exciter is omitted and the field winding of the alternator is supplied from the rectifier 17, 18, 19.