196 



ARMATURE CONSTRUCTION 



voltage. This pressure thus exists between groups of conductors 

 lying very near together and in adjacent slots, and at this point 

 the armature is most liable to insulation breakdown. 



Turning now to the corresponding half-coiled windings of Figs. 

 219 and 220, the full pressure exists between the groups of con- 

 ductors IA and GA ; but in this case these groups are distant from 

 each other by a space equal to the pole pitch, and, consequently, 

 the risk of breakdown is not nearly so great. 



FIG. 235. Parallel-connected Winding. 



This is a point decidedly in favour of the half-coiled style of 

 winding, and this point, together with the others enumerated, adds 

 to its wide utility for three-phase windings. 



The difficulty with the ordinary winding of the full pressure 

 existing between adjacent coils can be obviated by connecting two 

 halves of the winding in parallel, as indicated in Fig. 235. The 

 right-hand half of this winding, consisting of three coils, has 

 terminals S x and T x ; and the left-hand half, S 2 and T 2 . 



Connecting S 1 to S 2 and T x to T 2 puts the two halves in 

 parallel, and the full pressure occurs between the points S and T, 

 which are very remote from one another being, in fact, diametrically 



