64 



ELECTRICAL ENGINEERING 



(4) Fig. 53 represents the magnetic circuit of a bipolar dynamo. 

 It consists of a number of parts of different materials as follows; 



1 yoke y of section A v , length l y , and permeability fiy, 



2 pole cores c,c of section A c , length l c , and permeability JJL C) 

 2 pole pieces p,p of section A PJ length l p , and permeability H P) 

 2 air gaps g,g of section A g , length l g , and permeability I, 



1 armature a of section A a , length l a , and permeability /* a . 



e 



e 



Yoke ly ky 



O 

 





 

 

 



Air Gap lg A0r 



O 





 

 

 

 







e 

 e 



e 



Armature l a A a /"a 

 FIG. 53. Magnetic circuit of a dynamo. 



The reluctance of these parts are, respectively, 





97 97 



^ I P <*? _ ^ l a 



A pjlp A g 



and the reluctance of the whole circuit is 



The m.m.f. M is provided by field coils placed on the pole cores 

 as shown, and the flux through the circuit is 



= M M 



~ ~ ' 



