178 ARMATURE CONSTRUCTION 



is thus a twelve-slot winding. Adhering to the denomination 

 described above, its title would be a twelve-slot, single phase, 

 whole - coiled, sextuple coil, lap winding. This title wholly 

 describes the winding with the exception of the number of 

 conductors per slot, which should be stated separately. 



The bent shaping of the ends of the coils, to make them lie up 

 together, will be noted. 



POLYPHASE WINDINGS. 



As was stated at a previous point, any polyphase winding is 

 derivable from a single-phase winding by superimposing on the 

 armature a number of separate single-phase windings at regular 

 and suitable intervals. Thus, if we take the elementary single- 

 phase winding .given in Fig. 197 (reproduced in Fig. 218) and 

 superimpose another similar single-phase winding, but displaced 

 from the original, as shown in Fig. 219, we obtain an elementary 

 two-phase winding (or quarter-phase, as it is sometimes, and more 

 correctly, called). 



We have in Fig. 219 distinguished the second phase by 

 colouring it red, and also by suffixing the letter B after the 

 number on each conductor, in distinction from A for the first 

 phase. 



It will be noted that conductor IA is situated midway between 

 conductors 1 and 2 ; and as the distance between the conductors 

 1 and 2 is equivalent to one pole pitch, it follows that the 

 second phase is displaced from the first by one -half of the pole 

 pitch. This displacement is one quarter of a double pole pitch, 

 which corresponds to a complete period in the E.M.F. wave; 

 hence the more correct designation is " quarter-phase " rather 

 than " two-phase." 



If we wish to obtain a three-phase winding, we must insert two 

 extra phases within the double pole pitch. This has been done in 

 Fig. 220, where we have now the three phases marked A, B, and C. 

 The conductors IB and lc are evenly disposed between conductors 

 IA and 3 A of phase A, and each is displaced from the other by 

 one- third of a double pole pitch. Thus the displacement of the 

 phases is one-third of the period. 



The windings shown in Figs. 221, 222, and 223 are closely 

 related to the windings of Figs. 218, 219, and 220, and they have 

 been drawn immediately under them for the purpose of giving a 

 clear view of the elementary polyphase windings. The difference 

 between the upper and lower groups of windings is, that while in 



