GB718023A - Improvements in or relating to control apparatus for synchronous electric machines - Google Patents

Abstract

718,023. Automatic control systems for synchronous machines. GENERAL ELECTRIC CO., Ltd., FRIEDLANDER, E. S., MILNER, M.,.and GARDINER, H. W. B. Aug. 7, 1952 [Aug. 10, 1951], No. 18883/51. Class 38(4) [Also in Group XXXVI] In an automatic control system for a synchronous alternator (or motor) in which the reduction of field excitation on leading (or lagging) power factor loads is limited to maintain stability, the load current power factor is measured by comparing the phase of the output of a permanent magnet alternator driven by the shaft of the synchronous machine with that of tse main A.C. supply to or from the machine. The machine 10, Fig. 1, shown an an alternator, has a voltage regulator 16 energized from a potential transformer 15 via resistors 30, 31. The transformer 15 also energizes one winding 20 of a relay of the kind disclosed in Specification 613,856. The other winding 26 of the relay is energized from a permanent magnet alternator 12 driven by the main alternator 10. The armature 25 of the relay takes up a position dependent upon the phase relationship of the currents in the two windings and when the angular displacement between the magnetic axis of the rotor of the alternator 10 and the axis of the effective field thereof exceeds a predetermined amount, movement of the armature 25 causes contacts 27, 28 to be closed to energize motor 37 to rapidly increase the value of resistor 30. If the angular displacement is reduced, contacts 27, 29 energize motor 37 to slowly reduce the value of resistor 30 and also energize relay 33 which short-circuits resistor 27, 29 to open early and prevent overshoot of motor 37. In a modification, Fig. 2, a further resistor 52 is connected into circuit when the motor 37 is energized to increase the resistance 30 and so reduce the overshoot of the motor when running in this direction also. Additionally, the relay winding 26 is energized with alternating current having two components, one derived from the permanent magnet alternator 12, the other derived from the potential transformer 15 via a resistance condenser network 56, 55 dimensioned so that this component is equal and opposite to the component derived from the alternator 12 under normal conditions. In another modification; Fig. 3 (not shown), the ,second component is applied to an auxiliary winding on the relay. Specifications 662,761 and 706,992 also are referred to.