GB517468A - Improvements in and relating to dynamo electric machines - Google Patents

Abstract

517,468. Dynamo-electric machines; control of A.C. motors. ENGLISH ELECTRIC CO., Ltd., AYRES, W. E. M., and RICHES, A. J. July 23, 1938, Nos. 21888/38 and 8915/39. [Class 35] [Also in Group XXXVII] An alternating - current machine comprises a primary or field winding and a secondary or armature winding, the basic excitation being supplied to part of the primary or field' winding from an independent source such as an exciter and a component of excitation for armature. reaction compensation being supplied to another part of the same winding from a current transformer in the secondary circuit. The invention is particularly applicable to a synchronous motor or, as shown, to an induction motor 1 which is braked by supplying continuous current to the primary winding 1a and closing the circuit of the other winding through a variable resistance 2, In the case of a three-phase machine, current transformers 4 are connected in each phase of the secondary winding and feed, through rectifiers 5, two phases of the primary winding 1a, or they may feed the field winding of an exciter supplying two phases of the winding 1a. An exciter 3 is 'connected between the star point and the terminal of the remaining phase, or, to avoid the necessity of a star - point connection, the exciter may be connected between two of the phase terminals of the winding 1a. The exciter may be replaced by a transformer connected to an alternating current supply in conjunction with a rectifier. Alternatively, the exciter may be a low or variable frequency alternator in which case the transformers 4 and rectifiers 5 feed the field winding of an exciter supplying A.C. of the same frequency to the other phases of the winding 1a.