. Electric railways, theoretically and practically treated . ways in a similar manner. The system employed abroad,known as a three-phase induction motor system, required atriple trolley, was quite complicated, and the motors didnot possess the speed-torque characteristics of a direct cur-rent series motor. American engineers, therefore, devotedtheir attention to developing a single phase railway motor,which would possess speed-torque characteristics somewhatsimilar to the direct current series motor, in which thespeed increases with a decrease in load, and the torque perampere is constant with
. Electric railways, theoretically and practically treated . ways in a similar manner. The system employed abroad,known as a three-phase induction motor system, required atriple trolley, was quite complicated, and the motors didnot possess the speed-torque characteristics of a direct cur-rent series motor. American engineers, therefore, devotedtheir attention to developing a single phase railway motor,which would possess speed-torque characteristics somewhatsimilar to the direct current series motor, in which thespeed increases with a decrease in load, and the torque perampere is constant with a given impressed Withsuch a motor the questions of single circuit, car control, and ALTERNATING SINGLE PHASE MOTORS. sy power transmission would be extremely simplified. Withthis end in view, several types of A. C. motors were produced,to which the following theory will apply. Theory. — The direction of rotation of a series motor isindependent of the direction of the impressed , thedirection of rotation only changing when either armature C. Fig. 48. —SINGLE PHASE MOTOR WITH REVERSE SERIES COMPENSATING WINDING. or field circuit is reversed with respect to the other. It istherefore possible to operate a direct current series motorupon an alternating current source of suppl), inasmuch asthe current in the armature and field coils will reversesimultaneously. The ordinary type of direct current seriesmotor when operated upon an alternating current has a lowpower factor and low efficiency, due to the fact that addi-tional !^ of self-induction are set up in the wind-ings by the alternating magnetic flux. In addition to theseinductive £. J/./^.s, large hysteresis losses are present. 88 ELECTRIC RAILWAYS. The , of self-induction also exist in the alter-nating current single phase motor, but their effect in suchmachines is diminished by proper design. The usualmethod of procedure is to eliminate the armature inductiveE. M. F. and to reduce the field induct
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