. Electric railways, theoretically and practically treated . xciting coil F, and is directlyproportional to the rotational speed ofthe armature. The second ,Erp, is due to transformer action ofthe compensated coil T, and is there-^et fore proportional to the impressed fre-quency, and is in quadrature with in the compensated two ,Ep and E.^, aretherefore at right angles to each other (Fig. 56), producinga resultant E. M. F., which causes a magnetizing current toflow through the armature. These produce arotating field, elliptical inshape (Fig. 57), whi
. Electric railways, theoretically and practically treated . xciting coil F, and is directlyproportional to the rotational speed ofthe armature. The second ,Erp, is due to transformer action ofthe compensated coil T, and is there-^et fore proportional to the impressed fre-quency, and is in quadrature with in the compensated two ,Ep and E.^, aretherefore at right angles to each other (Fig. 56), producinga resultant E. M. F., which causes a magnetizing current toflow through the armature. These produce arotating field, elliptical inshape (Fig. 57), which be-comes circular at synchron-ism. At synchronous speedthe , Ep and E-r areequal, resulting in satisfac-tory commutation. Onegreat advantage with the re-pulsion motor with its dis-tributed winding is the largepole span which may beemployed, practically 180°.This increases the cross-sec-tion of air gap, permitting increased length of gap, or re-sulting in higher power factors with small gap. The repulsion motor has steeper speed and torque char-. Fig. 57.—DIAGRAM OF REPULSIONMOTOR FIELD. ALTERNATING SINGLE PHASE MOTORS. 97 acteristics than the direct current motor, as is illustratedby the curve sheet, Fig. 58. These curves were pre-pared by Walter I. Slichter in a paper presented to the REV. 1200 PER VIIN. i| \c. UOO n COMPARISON OF SPEED AND TORQUECURVES )F A REPULSION MOTOR AND A DIRECT-CURREN SERIES MOTOR, 500 VOLTS ON EACH v_ 5> \9 C 1000 % \l \; t^ -900 -90- \». r-CWf 1 1 BENTEFFICIEN :/ \ 1 r r \ . ■— -800 ^^.,J ■OOT LBS. IGOO \ \l; ^ r / -700 \ / ^ UOO \ // -600 6 \ A / / 1200 \J // \ / ~-^ 1000 / / \ / ^ 1 s \ / ,^ \ -300 / # \ -600 4 / / V X f ■^ .<^ f / y -100 ■f^ ^■^ / -200 / < 0 b i AMPERES Xt 506 VOL 1-JO ! luo 1 •-( TS0 :•■ 0 21- 0 Fig. 58.—COMPARISON OF CHARACTERISTIC CURVES OF D. C. AND A. C. MOTORS. A. in January, 1904. It is obvious from thesecurves that the efficiency of the direct current motor is 98 ELECTRIC
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