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PRINCIPLES OF ELECTRICAL DESIGN 



In the case of the wave, or series, winding there will be two 

 paths in parallel through the armature, whatever may be the 

 number of poles. Two sets of brushes will, therefore, suffice 

 to collect the current; but more sets may be used if desired, in 

 order to reduce the necessary length of the commutator. In 

 this case the brushes would be placed one pole pitch apart 

 around the commutator, and all brush sets of the same polarity 

 would be joined in parallel. This does not, however, increase 



FIG. 29. Diagram of simplex series winding. 



the number of electrical paths in parallel in the armature, but 

 merely facilitates the collection of the total current, as will be 

 understood by carefully studying the winding diagrams. The 

 series winding is usually adopted when the voltage is high and 

 the current correspondingly reduced; it is, therefore, rarely neces- 

 sary to provide more than two sets of brushes. When a greater 

 number cf brush sets is provided on a series-wound machine, 

 it is not easy to ensure that the current will be equally divided 

 between the various sets of brushes. What is known as selective 



