GB690175A - Improvements relating to electric motor control systems - Google Patents

Abstract

690,175. Cores for dynamo-electric machines. ENGLISH ELECTRIC CO., Ltd. March 2, 1951 [March 17, 1950], No. 6711/50. Class 35. [Also in Group XXXVII] In a control system for D.C. motors having bifurcated poles and separate field windings on each pole leg, the range of speed is extended by first reducing the excitation on the pole legs assisted by the armature m.m.f., and then the excitation due to the other field winding. Fig. 2 shows the flux condition of a D.C. series motor having the salient poles bifurcated into two legs 1a, 1b (preferably spaced 60 degrees electrical) carrying field coils 2, 3. The inclined line 24 indicates the m.m.f. of the armature and the broken lines 25, 26 indicate the m.m.f's of the coils 2, 3 respectively. The closure of the contactors in the motor field circuit produces a different resultant m.m.f. according to which contactor(s) is closed. The lines 27, 30, 31 are resultant m.m.f's under the leg 1a and the lines 28, 29 are resultant m.m.f's under the other leg 1b. The lines 29, 31 indicate the resultant m.m.f's under the legs 1b, 1a when the appropriate contactors are operated. Thus the voltage between the commutator bars will be reduced because of the reduction of the resultant m.m.f. In a modification, the armature is in series with a single field winding 33, Fig. 3 (not shown), made up from coils on legs 1a, separately excited windings 34, 35 being respectively provided on legs 1a, 1b.