. Electric railways, theoretically and practically treated . ting field pro-duced by stationary windings, the rotating field beingsimilar to that of an induction motor, having a distributedsingle phase winding. The armature terminals are shortcircuited at the brushes, there being no electrical connec-tion between armature and field coils. The rotating fieldmay be produced by winding .two coils at right angles toeach other (Fig. 54), one being the field proper with few ALTERNATING SINGLE PHASE MOTORS. 95 turns, and the other winding a transformer secondary withmany turns. The ratio of these tur
. Electric railways, theoretically and practically treated . ting field pro-duced by stationary windings, the rotating field beingsimilar to that of an induction motor, having a distributedsingle phase winding. The armature terminals are shortcircuited at the brushes, there being no electrical connec-tion between armature and field coils. The rotating fieldmay be produced by winding .two coils at right angles toeach other (Fig. 54), one being the field proper with few ALTERNATING SINGLE PHASE MOTORS. 95 turns, and the other winding a transformer secondary withmany turns. The ratio of these turns corresponds to theratio of the armature to the field Thisform of repulsion motor is termed the compensated with the straight series motor, high power factors maybe obtained with the compensated motor by a large num-ber of transformer turns and few field turns. The twoexciting coils obviously produce a resultant field for whicha single coil (Fig. 55) may be substituted. This repul-sion motor was developed by Professor Elihu Fig- 55.—THOMPSON REPULSION MOTOR. The action of the repulsion motor corresponds to thatof a transformer with stationary secondary, and movableprimary, the primary being placed at a definite angle tothe secondary, the repulsion existing between the primaryand secondary causing rotation. The displacement of theshort-circuited brushes, w. Fig. 55, corresponds to thisrelative angle existing between primary and secondary ofthe transformer. The smaller this angle the higher will bethe power factor. An angular brush displacement of 15°appears to be the minimum limit, yielding power factors offrom .90 to .97, 96 ELECTRIC RAILWAYS. Fig. 56.—RELATION OFARMATURE A clearer conception of this repulsion motor may beobtained by considering the compensated type (Fig. 54).With this motor two , island Ej,, are induced inthe armature conductors. Ep is caused by the flux fromthe field exciting coil F, and is directlypropor
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