70 THE DESIGN OF STATIC TRANSFORMERS 



reactance S in ohms is the quotient of the terminal pressure 

 and the magnetising component, and hence is equal to 



= 24>70 hms - 



The reactance S is, however, also equal to 2 TT oc I, where I is 

 the inductance in henrys. Therefore 

 24700 



The inductance might also have been estimated in the follow- 

 ing manner. Since the total flux passing through the iron 

 core is equal to 0,73 megalines, and since the magnetising 

 component of the no-load current is equal to 0,203 amp 

 (or 0,203 X A/2 = 0,286 crest ampere), the flux per ampere 

 becomes equal to 



73 

 ^ = 2,55 megalines. 



There are 3100 primary turns, and therefore the inductance 

 may be found as follows : 



3100 X 2 550 000 

 I = - - = 79 henrys. 



We have seen on the previous page that for the power 

 factor, G, of our 20-kw transformer, we have, at no load, 

 the value 



G = 0,185. 



The power factor increases rapidly as the load on the trans- 

 former increases. We have seen that at no load the wattless 

 component of the current flowing into the transformer (i.e., the 

 magnetising component) is 0,203 ampere, and that the energy 

 component (i.e., the core-loss component) is 0,038 ampere. The 

 full load secondary current is 100 amperes. When the secondary 

 current is 10 amperes there must be an equivalent energy com- 

 ponent flowing into the primary windings to provide it. 

 Since the ratio of transformation is (5000 : 200 = ) 25 : 1, 

 this energy component flowing into the primary will be 



