GB929120A - Means for initiating the direct current excitation of self-excited dynamo-electric machines - Google Patents

Abstract

929,120. Exciting dynamo-electric machines. SELECTRA Ltd. Nov. 27, 1959 [Dec. 5, 1958], No. 39355/58. Class 35. Excitation of an A.C. or D.C. generator is initiated by a permanent magnet generator permanently connected through rectifiers to the field winding of the main machine in series or parallel with the normal excitation means. In a single phase form shown, the field winding 20 of a generator 10 is fed from the permanent magnet generator 15, 16, and also by the conventional excitation system, e.g. compound, at leads 11, 12. The reactance of the exciter winding 16 may be matched at the rated speed by a series condenser 17 so that the exciter voltage is independent of the current taken by the main field winding. The condenser may be connected through a series transformer for voltage matching. Alternatively the exciter may be compounded. The exciter voltage is lower than the normal excitation voltage so that once this has been initiated the rectifier 18 prevents further flow of current from the exciter. The exciter may be driven directly or through increasing gearing from the main machine or it may be separately driven. A three-phase form is described in which the exciter windings are connected in series with condensers and are connected to the rectifier through a tapped variable ratio transformer or matching impedances. The full-wave rectifier may be replaced by a halfwave rectifier and smoothing condenser. In this case two field windings are used, the normal excitation circuit feeding one of them and the initiating circuit feeding both in series. The main machine 10 may be an inductor alternator exciting a large power generator. Specifications 719,212 and 719,267 are referred to.