GB570838A - Improvements in and relating to dynamo-electric machines - Google Patents

Abstract

570,838. Dynamo-electric machines. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 22, 1942, No. 18211. Convention date, Dec. 31, 1941. [Class 35] In a cross-field machine, auxiliary excitation is provided from an A.C. source to minimise the effect of residual magnetism. The Figure shows an armature reaction excited machine comprising an armature 30 having primary and secondary brushes 14, 15 and 16, 17 respectively and rotating in a magnetic frame 10 having split poles 11, 12 provided with polepieces 22, 23 and 24, 25 respectively. The brushes 14, 15 are shortcircuited through primary exciting windings 18-21 arranged on the polepieces and producing fluxes 26 aiding the primary armature reaction 27. The load characteristics of the machine are controlled by a separately excited winding 29 on each of the poles 11, 12 and producing a flux 30 opposing a secondary armature reaction 28, the speed of response of the machine to variations in excitation of the winding 29 being improved by windings 33 which compensate for secondary armature reaction. The effects of residual magnetism and hysteresis are reduced by a transformer 35 which supplies alternating current of peaked wave form to terminals 38, 39 of the primary exciting winding, as shown, so as to provide alternating excitation components 40 of reverse polarity in adjacent polepieces. In a modified construction, there are no windings common to the two polepieces, such as the windings 29, 33, the windings being provided on each individual polepiece, and in one such arrangement the primary exciting winding is omitted, the primary brushes being short-circuited and the alternating current component introduced into the circuit of the secondary armature reaction compensating winding. Specifications 539,835 and 556,397 are referred to.