. Electric traction and transmission engineering . Fig. 12. of a Scott transformer, each phase of which supplies single-phase current to the motors on one side of the 12 shows the scheme of connections. There are several types of alternating-current single-phase railway motors at present in operation, but of thesethe compensated series motor is the only one used in thiscountry. Repulsion motors are used abroad to a consid-erable extent; single-phase induction motors starting asrepulsion motors have not been seriously considered fromthe railway viewpoint. TYPES AND PERFORMANCE CURV
. Electric traction and transmission engineering . Fig. 12. of a Scott transformer, each phase of which supplies single-phase current to the motors on one side of the 12 shows the scheme of connections. There are several types of alternating-current single-phase railway motors at present in operation, but of thesethe compensated series motor is the only one used in thiscountry. Repulsion motors are used abroad to a consid-erable extent; single-phase induction motors starting asrepulsion motors have not been seriously considered fromthe railway viewpoint. TYPES AND PERFORMANCE CURVES OF MOTORS. 29 Series Motors. — Consider a direct-current armaturemounted within a single-phase alternating magnetic field,as in Fig. 13. When the armature is stationary an electro-motive force will be induced in the armature turns, dueto the alternating flux which passes between the fieldpoles. The greatest will be induced in the turnsperpendicular to the field axis, since these turns link with. Fig. 13. the greatest number of lines of force; and no willbe induced in the turns in line with the field axis. Thedirections of the induced in the armature turnsby the change in field flux are indicated in the figure bythe full arrows, and it is seen that the maximum value ofthis is across BC. As in transformers, the effec-tive value of this electromotive force is 2*f*mN ET - —p—-> (1) V2 IO8 where <£m is the maximum value of the flux entering the 30 TRACTION AND TRANSMISSION. armature and N is the equivalent number of armatureturns. The maximum number of lines of force linked with asingle turn depends upon the position of this turn in themagnetic field, and is proportional to the greatest value of<£m times the cosine of the angle of displacement of theturn from the position AD. Assuming the turns to beevenly distributed over the periphery of the armature, theaverage value of the maximum flux linked with the arma- 2 ture turns will be
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