222 



ARMATURE CONSTRUCTION 



In three-range windings, owing to the dissimilarity of the coils 

 in the different ranges, there is a danger of the length of the mean 

 turn of a coil in one range differing from that of the other ranges, 

 which renders the phases of different reactance and unbalanced. 



In such a winding as Fig, 253 the coils are, however, much of 

 the same size ; but with a winding as type e in Fig. 230, this is 

 not so. This is obviated by the grouping of Fig. 256, which is the 

 diagram for the machine shown in Fig. 255. This is a 4000 k.w. 

 10,000 volt 36-pole three-phase alternator, of the Lahmeyer Co. 



FIG. 258. Stator Winding with similarly shaped Coils. 



The title of the winding is a three-phase, whole-coiled, double-coil, 

 four-slot spiral winding in three ranges. 



A portion of the winding is shown in Fig. 257, which makes 

 the details more clear. In this winding, as distinguished from the 

 previous one, every alternate group of three coils is reversed so 

 that the upper range coil of one group comes next to the upper 

 range coil of the neighbouring group. The effect of this, as will 

 be seen from the coloured phases in Fig. 256, is as follows : 



The coils of the red phase are all of the same and medium 

 breadth. 



The coils of the black phase are half broad and half narrow. 



The coils of the blue phase are half narrow and half broad. 



