Fig. 256.—Developed view of the four pole field shown in perspective in [fig. 255].
Ques. What is lap winding?
Ans. One in which the ends of the coils come back to adjacent segments of the commutator; the coils of such a winding lap over each other.
Ques. What is a wave winding?
Ans. One in which the coil ends diverge and go to segments widely separated, the winding to a certain extent resembling a wave.
Fig. 257.—Development of ring winding of four pole machine shown in [fig. 254]. The dead wire or inactive inductors on the inside of the ring are shown in dotted lines, the full lines representing the active portion of the winding.
Angular Pitch or Spread of Drum Coils.—Before taking up the winding as a whole, the form of the individual coil should be considered. [Fig. 260] shows an end view of one coil in position on a drum armature of a multipolar machine. The two slots X and Y contain the sides of the coil and the distance between them on the surface of the drum is called the angular pitch or spread of the coil. Theoretically this is equal to the pitch of the poles, represented by the angle M, which is the angle between the pole centres.
