86 



PRINCIPLES OF ELECTRICAL DESIGN 



the individual coils. Thus, if the two ends of the coil shown in 

 Fig. 26 are connected to neighboring commutator bars, as in 

 Fig. 27a, we obtain a multiple or lap winding, while, if the ends 

 are taken to commutator bars approximately two pole pitches 

 apart, (Fig. 276), we obtain the series or wave winding. The im- 

 portant distinction between these two styles of winding is the 

 fact that, with the multiple winding, there are as many sets of 



(a) 



(b) 



rc (Approxima tely)~. 



P 



FIG. 27. Multiple and series armature coil connections. 



brushes and as many paralled paths through the armature as there 

 are poles while, with the series winding, there are only two elec- 

 trical paths in parallel through the armature, and only two sets of 

 brushes are necessary, although a greater number of brush sets 

 may be used. 1 



1 What are known as simplex windings are here referred to. Multiplex 

 windings may be used on lap-wound machines when the current is large and 

 it is desired to have two or more separate circuits connected in parallel by 

 sufficiently wide brushes. This tends to improve commutation. In series- 

 wound machines the multiple winding has the advantage that it enables 

 the designer to obtain more than two circuits hi parallel, but not as many 

 as there are poles. In this manner it is possible to provide for a number of 

 parallel paths somewhere between the limits set by the simplex wave and 

 lap windings respectively. These windings are, however, rarely met with. 

 Again, a duplex winding may be singly re-entrant or doubly re-entrant. 

 In the former case, the winding would close on itself only after passing twice 

 around the armature, while, in the latter case, there would be two inde- 

 pendent windings. It is suggested that the reader need not concern 

 himself with these distinctions, which have no bearing on the principles of 

 armature design. More complete information can be found in many text- 

 books and in the handbooks for electrical engineers. 





