ALTERNATING-CURRENT WINDING 205 



An individual coil would appear as shown in Fig. 242 ; but it 

 is too tedious to draw out all the coils in this manner, so long as 

 the number of conductors per slot is stated and borne in mind. 



In Fig. 241 we have drawn six coils with full lines and six 

 with dotted lines. The six full-line coils represent the front 

 range, and the dotted coils the back range. This plan is useful to 

 distinguish between the ranges in the case of two-range windings, 

 and does not confuse with the distinction between the phases 

 where different colours are used for each phase. 



In Fig. 241 we have not connected up the coils to one another, 

 as this particular winding possesses the property that it may be 

 connected as either a two-phase or a three-phase winding. We 

 shall demonstrate this by connecting it up in both ways. 



Two-phase. For a two-phase winding, as there are twelve coils, 

 there must be six coils per phase ; and one phase will take in the 

 six coils in one range, and the second phase the six coils in the 

 other range. Thus phase A must consist of the coils numbered 

 I, III, V, VII, IX, and XI ; phase B of coils II, IV, VI, VIII, X, 

 and XII. Now, since the neighbouring coils of one phase lie close 

 together for instance, see the group of conductors 10, 11, and 12, 

 and the group 13, 14, and 15 with no space between them, we 

 must arrange for one coil per phase per pole. Thus we shall have 

 six poles, one subtending each coil of one phase ; and in 

 connecting up the coils we must arrange for the direction 

 of current circulation in adjacent coils to be opposite (see 

 Figs. 203 and 204). 



Hence we connect the end of coil I to the end of coil III, the 

 beginning of III to the beginning of V, and so on, reversing each 

 coil on its predecessor and making it of opposite polarity. 



Had we connected up the coils all in the same sense, we should 

 have required twelve poles; but this would be impracticable, 

 as there is no room between the adjacent coils (as, for instance, 

 between coils I and III) for the other six consequent poles. 



Connecting up the other phase in a similar way gives us a 

 six-pole two-phase winding, with terminals S A T A , S B T B , as in 



fig. 243. 



72 

 The number of slots per pole is =12, or six per pole per 



phase. As this winding has one coil per phase per pole, a single 

 coil should cover six slots on both sides, i.e. three on each side 

 (see p 174) ; this, it will be seen, is the case in the winding 

 diagram. 



