GB633091A - Improvements in or relating to electric alternators - Google Patents

Abstract

633,091. Automatic regulation. GENERAL ELECTRIC CO., Ltd., and FRIEDLANDER, E. S. Jan. 6, 1947, No. 438. [Class 38 (iv)] The output frequency of an alternator is maintained substantially constant irrespective of the speed of the alternator by compensating speed variations by rotation of the exciting field in one or other direction at a speed corresponding to the difference-frequency between the speed frequency and the constant frequency of a master oscillator. In the arrangement shown in Fig. 1, an alternator having a single phase stator 3 and a two-phase rotor 2 drives a tachometer generator 10 having a D.C. field 11 supplied from a master oscillator at 14 through rectifiers 12 and four stator windings 15-18 which generate voltages 90 degrees phasedisplaced. These voltages are independently added in a transformer 32 to a voltage on winding 27 derived from the master oscillator and the resultants are rectified by rectifiers 19-22. The pairs of resultant voltages which are phase-opposed are then applied to the grids of pairs of amplifiers 23, 24 and 25, 26 to produce in the supply lines to the rotor, twophase voltages of difference frequency, when there is lack of synchronism between the alternator speed and the correct output frequency. Thus, when the speed is correct, the rotor field rotates at the same speed as the rotor but any change of speed causes relative rotation of the rotor field so as to maintain the output frequency constant. In a modification, a three-phase rotor is provided, the supply to the rotor being derived from the difference currents from the master oscillator and a three-phase exciter driven from the' alternator. Comparison is effected through phase-shifting networks and mesh-connected grid-controlled rectifiers. The phase-shifting networks are also subject to bias voltages dependent on the ratio of the circulating currents in the rectifiers and the alternator field currents, so as to ensure that the circulating current is greater than the peak amplitude of the field currents to keep the rectifiers output above zero. Specifications 589,526, 597,882, 602,870 are referred to.