236 ARMATURE CONSTRUCTION 



300 k.w. 440-volt three-phase alternator. The current per phase 

 is 460 amperes at full load, arid, at a current density of 200 

 amperes per sq. cm., the cross section of conductor required to 



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carry this current would be = 2'3 sq. cms. As this is a very 



large conductor to handle, the winding would have to be carried 

 out as a bar winding, and preferably with straight bars and 

 separate V-end conductors with a joint at the end of each bar, 

 i.e. two joints per bar, or, as there are 480 conductors, a total of 

 480 joints. A large solid conductor is undesirable on account of 

 eddy currents, and it would be better to replace the single con- 

 ductor by two conductors in parallel, each of one half the cross 

 section. The other alternative is to employ a stranded conductor, 

 but this again is undesirable on account of the space lost in the 

 slot due to the stranding. 



If we take two conductors per slot we are at once able to 

 carry out the winding as a retrogressive wave winding, but it will 

 be necessary to connect the two halves of the winding in parallel, 

 and not in series, as in Figs. 273, 274, and 276. 



The diagram in Fig. 277 shows a portion of the winding 

 (corresponding to about four poles) with the terminals brought out 

 and the parallel connections made. The arrow-heads on the con- 

 ductors and on the terminal lines indicate the relative directions 

 of the E.M.F.'s, and the winding is connected up in the correct 

 sense with regard to these directions. The method of parallel 

 connecting will be more clear from Fig. 278, which shows one 

 phase of a similar winding having only six poles but three slots 

 per pole per phase, as in Fig. 277. 



Commencing in Fig. 278 with conductor No. 1, and progressing 

 round the winding in one direction, taking in the appropriate 

 conductors, we arrive at conductor No. 96. Similarly for the 

 other half of the winding, commencing at No. 6, we arrive finally 

 at No. 19. The arrow-heads indicate the relative directions of the 

 E.M.F.'s, and for the proper sense we must connect conduct" > 

 1 and 6 together, and also 96 and 19 together, obtaining the 

 terminals T x and T 2 , between which there are two equal halves of 

 the winding in parallel. Fig. 278 should make these connections 

 quite clear, and also the similar connections for each of the phases 

 in Fig. 277. The advantages of this winding in this case are : 

 (1) That the conductor is much more workable, owing to its IKM'H- 

 of smaller section ; (2) the number of joints at the ends is only one 

 half of the number in the original wave winding with one conduct") 



