ARMATURE WINDINGS 



257 



or bent so as to clear the other coils, generally as shown in 

 Fig. 97. 



All the conductors of one phase are usually connected in 

 series, but sometimes parallel circuits are used. It then becomes 

 a matter of importance to see that there is no phase difference 

 between the e.m.fs. generated in the conductors of parallel 

 circuits. In other words, the conductors of parallel circuits 

 should be so disposed in the available slots that they cut the 

 same amount of flux at the same instant of time. Having 

 mentioned this point, it does not appear necessary to enlarge 

 upon it. 



FIG. 97. End connections of single-layer armature winding. 



79. Spread of Windings. In two-phase and three-phase 

 machines, all the slots on the armature are utilized. With 

 full-pitch windings, 1 the number of slots per pole is divisible by 

 2 for a two-phase generator, and by 3 for a three-phase generator. 

 Thus, with distributed windings (more than one slot per pole 

 per phase), the "spread," or space occupied by each phase wind- 

 ISO 

 ing, is ^- = 90 electrical degrees for a two-phase machine, and 



Z 



180 



- = 60 degrees for a three-phase machine. 



In single-phase machines, nothing is gained by winding all 

 the slots on the armature surface; after a certain width of wind- 

 ing has been reached, the filling of additional slots merely in- 

 creases the resistance and inductance of the winding, without any 

 appreciable gain in the matter of developed voltage. This is 



1 Short-pitch windings are very common in two-*pole machines, as they 

 tend to simplify the end connections. In this case the double-layer winding, 

 as in D.C. machines, would be used. 

 17 



