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ELECTRICAL MACHINERY 



nearly always has two coil sides per slot and sometimes 

 more.) As each coil has two sides we shall require 12 coils 

 to wind the armature. 



Single Phase Winding. If the armature is to be wound 

 single phase only 8 coils will be used, some of the slots being 

 left vacant; if a two-phase or three-phase winding is to be 

 wound, all slots will be used. In the first case two groups 

 of six coils will be used and in the latter case 3 groups of 4 

 coils each. 



Now these coils may be all full pitch (a coil reaching 

 from the center of one pole to the center of the next pole) 



FIG. 142. Formed, Concentric Coils for an a-c. Armature. The 

 smaller coil is shown completely covered with its insulating cov 

 ering; the larger coil is not yet insulated. 



or the coils may be wound concentric, in which case some 

 of the coils must be fractional pitch. If the coils are all full 

 pitch they are all of the same shape and placed on the 

 armature just as though a continuous current, lap winding 

 were being formed; the only difference from a c-c. winding 

 would be in the end connections of the coils. 



If the winding is to be for a small, low-voltage machine, 

 full pitch, lap-coils will very likely be used, but if the winding 

 is for a large, high-voltage machine, the concentric coils 

 are nearly always used. 



