PARTS OF A DYNAMO-ELECTRIC MACHINE 41 



these paths may be assumed the same * as that of the path 

 shown in Fig. 15 because that portion shown by the dotted 

 lines is the same in both figures and this is the greater 

 length of the path. The e.m.f. acting in one path of Fig. 

 16 is only one-half of that in the path of Fig. 15 and hence 

 the current in one path of Fig. 16 will be one-half of that 

 in Fig. 15. Hence the PR loss per path will be one-quarter 

 as large, but as there are two paths in Fig. 16 and only one 

 in Fig. 15 the PR loss in the divided core will be one-half 

 as great as that in the laminated core. 



FIG. 16. Eddy Current Paths when the Core has been Divided into 



two Parts. 



If the division is carried further, the PR loss due to 

 eddy currents is still more reduced and by using very thin 

 sheets this source of loss may be nearly eliminated. In 

 commercial machines the laminations are generally 0.014" 

 thick. The laminations may be insulated from one another 

 on large machines by a coat of insulating paint on each 

 lamination; on small machines the oxide coating, formed 

 on the iron sheet while it is being annealed, is relied upon 



* This approximation is more nearly true as the thickness of the 

 laminations is decreased. 



