. A text-book of electrical engineering;. on ofrotation will be reversed. 112. The Rotary Field in a Three-phase Motor 359 112. The Rotary Field in a Three-phase Motor. The armature of a three-phase generator contains three separate wind-ings, displaced from each other by 120°. (Fig. 364). Care must be takenwhen drawing the windings, that the beginnings i, 2, and 3, of the threephases are 120° apart, and that, starting from these points, each phase-winding passes round the armature in exactly the same direction. In , for example, each winding commences by passing inwardly across thefron
. A text-book of electrical engineering;. on ofrotation will be reversed. 112. The Rotary Field in a Three-phase Motor 359 112. The Rotary Field in a Three-phase Motor. The armature of a three-phase generator contains three separate wind-ings, displaced from each other by 120°. (Fig. 364). Care must be takenwhen drawing the windings, that the beginnings i, 2, and 3, of the threephases are 120° apart, and that, starting from these points, each phase-winding passes round the armature in exactly the same direction. In , for example, each winding commences by passing inwardly across thefront end of the ring. These windings are connected by means of slip-ringswith the corresponding terminals of the stator of the motor. The fact thatthe generator has been numbered clockwise and the motor in the oppositedirection is immaterial, and has been adopted to avoid crossing the con-nections. Phase I, i is shown in Fig. 364 under the middle of the pole and, ifphase displacement due to self-induction be neglected, the current in this. QetijeratoT Motor Fig. 364 phase will have its maximum value. The instantaneous value of the currentin the other phases will be A A i = 30° = 0-5 i. By tracing out the current in the various coils of the stator, it is seenthat the coil-sides 3, i and 2 carry current in the same direction, and maybe grouped together with respect to their magnetic effect. The same is trueof the coil-sides 2, i and 3, although they belong to three separate resultant magnetic field will evidently be as indicated by the dottedlines, and the poles as shown by the letters iV and S. The state of affairs a twelfth of a period later is shown in Fig. 365. Thegenerator has turned through 30°, and the phase-winding 3, 3 is now in theneutral zone and therefore without current. In the other two phases themomentary value of the current is A A i = i. sin 60 = 0866 ».The coil-sides i and 2 of the motor may now be grouped together, andsimilarly 2 and i. The
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