ROTOR WINDING 119 



126 49 74 

 3285176 

 5_305378 

 7325580 



We have now used up half the conductors of the phase, and at 

 this stage a fresh difficulty arises. All the odd conductors in Group 

 I have been used up, so that we cannot proceed from conductor 80 

 (which is the last even conductor in Group IV) to an odd conductor 

 in Group I. A pitch of 25 gives conductor 80 + 25 = 105, or 9, 

 which does not belong to our phase at all. The nearest odd conductor 

 in Group I is 7, but this has already been made use of. If we try 

 going back to Group III, we again find that all the odd conductors 

 have been used up. Two possible courses are open to step forward 

 to Group I, using the even conductor 2 of this group, or to go back 

 to Group III, using the nearest even conductor corresponding to 

 a pitch of 24 (i.e. conductor 80 24 = 56). In either case, the even 

 conductor 80 will have to be connected to another even conductor. 

 It will be found, however, that if we go forward to Group I, we shall 

 involve ourselves in still further difficulties, necessitating further 

 irregularities in the winding ; whereas by going back to Group III, 

 thereby reversing the original direction of travel around the rotor 

 circumference, and continuing to step round in this reverse direction, 

 we encounter no further difficulties, the winding proceeding exactly 

 as before, the only difference being in the negative sign of the pitches. 

 We thus complete the winding as follows : 



5631879 



5429 6 77 

 5227475 

 50 25 2 73 slip-ring 



The peculiarities exhibited by the above example are characteristic 

 of every rotor bar winding of the wave type in which the conductors 

 are arranged in two layers. In each case, we have to (1) break the 

 alternate sequence of the pitches after the completion of each 

 revolution ; and (2) take a backward step, represented by the mean 

 pitch, thereby reversing the direction of travel after the completion 

 of half the winding, when the odd and even conductors in alternate 

 groups respectively have been used up. 



If, however, the conductors are arranged in a single layer, with 

 evolute end connectors (instead of the "straight-out" or "barrel" 

 type), there is no reason why an even pitch should not be used. In 

 that case, after each revolution, the normal pitch must be increased 

 by unity. Taking the example just considered, but assuming the 



