40 ELECTRICAL MACHINERY 



field, an e.m.f. is generated in it (any conductor moving 

 through a magnetic field so as to cut lines of force has an 

 e.m.f. induced in it); the direction of this e.m.f. is parallel 

 to the shaft, i.e., lengthwise of the armature core. Under 

 a N pole it is in one direction and under a S pole in the 

 opposite direction. As the solid iron core may be considered 

 as one large conductor it is evident that these e.m.fs. in 

 the armature core will cause currents to circulate in the 

 core. The direction of these currents is shown by Fig. 



North Pole 



> Shaft 



Armature 

 core 



South Pole 



FIG. 15. Path of Eddy Currents in a Solid Armature Core. 



15, which represents a section of the core, taken parallel 

 to the shaft. The direction of the e.m.f. induced in the 

 core is shown by the solid arrows and the path of the eddy 

 current is shown by the path formed by these arrows and 

 the dotted lines. 



Reduction of Eddy Current Loss by Laminating the Core. 

 Now if the core is made of two parts, insulated from one 

 another as in Fig. 16, the eddy currents will have to flow 

 in two separate paths as shown. The resistance of each of 



