150 



PRINCIPLES OF ELECTRICAL DESIGN 



currents is especially useful when calculations are made, as will 

 frequently be found convenient, by considering the separate 



Fia. 57. Flux in commutating zone due to armature m.m.f. only. 



component fluxes due to distinct causes, all combining to pro- 

 duce the actual or resultant flux. It is not difficult to see that 

 the flux shown in Fig. 57 is never such as to generate an e.m.f. 



FIG. 58. Flux in commutating zone near leading pole tip. 



tending to reverse the current in the short-circuited conductor. 



Consider now Fig. 58. The main poles have been excited 



and the brushes moved forward until a satisfactory commutating 



Date. 



