52 



ELECTRICAL MACHINERY 



to this external circuit reverses also, thus maintaining on 

 the external line a uni-directional e.m.f. 



Construction of the Commutator. The function and 

 action of the commutator will be taken up in detail in 



FIG. 26. Commutator for Small 500-volt Motor. General Electric Co. 



Chapter III; here we shall consider only the mechanical 

 features of the commutator. It consists essentially of a 

 set of copper bars, formed in such a shape that when 

 assembled, they form a hollow cylinder. As they are 

 assembled insulation is put betweem adjacent bars so that 

 every bar is well insulated from every other. The commu- 

 tator for a small machine is shown in Fig. 26, and Fig. 27 

 shows the assembled commutator of a large railway 

 generator. 



