218 ARMATURE CONSTRUCTION 



we should need three varieties of lines, which becomes complicated. 

 It is better to distinguish the ranges on the developed diagram by 

 drawing one range with broad coils, the second with coils of 

 medium breadth, and the third with narrow coils. A diagram on 

 these lines is shown in Fig. 254, which is the diagram for the 

 winding of which a photograph is given in Fig. 253. 



This winding is of the type g shown in Fig. 230, having one 

 range bent back away from the air-gap, the second range pro- 



FIG. 253. Three-phase, Half-coiled, Double-coil, Two-slot Spiral Winding 

 in three ranges (six-phase grouping). 



jecting out straight, and the third range bent forward over the 

 air gap. 



The bad feature of this winding where one range is bent over 

 the air-gap, is that the rotor cannot be withdrawn without taking 

 off the top half of the armature. In the case of large armatures 

 this does not matter, as they are invariably built in at least two 

 sections for convenience in manufacture and transport. 



The winding of Figs. 253 and 254 is arranged in groups of 

 three coils each, and this armature can be divided at any point 

 between any pair of groups without disturbing the winding at all. 

 The diagram shows two such groups connected up. 



This winding is identical with that given in Fig. 229, and its 



