62 



THE MAGNETIC CIRCUIT 



[ART. 25 



2-/<P m ; hence the effective value is 27r/0 Tn /v / 2 = 4.44/0 m . Let 

 there be N\ primary turns in series; the total primary voltage is 

 then equal to NI times the preceding value. Expressing the flux 

 in megalines we therefore obtain the following practical formula 

 for the induced voltage in a transformer: 



(28) 



Coils 



Coils 



FIG. 13. A shell-type 

 transformer. 



Mica 



Shields 



FIG. 14. A cruciform-type 

 transformer. 



In practice, EI is assumed to be equal and opposite to the applied 

 voltage (for calculating the flux only, but not for determining the 

 voltage regulation of the transformer). Formula (28) holds also 

 for the secondary induced voltage E 2 if the number of secondary 

 turns in series N 2 be substituted for NI . The voltage per turn is 

 the same in the primary and in the secondary winding; therefore, 

 the ratio of the induced voltages is equal to that of the number 



