374 



ELECTRICAL EQUIPMENT 



condition, i.e., no current flowing in the secondary winding. The 

 primary e.m.f. OB, causes an exciting current OM\ to flow, this 

 current consisting of two components MM\, and OM. The com- 

 ponent MM i is in phase with the e.m.f. and supplies the iron core 

 loss due to hysteresis and eddy currents, while OM, which is in 

 quadrature with the e.m.f., represents the magnetizing current 

 and is thus in phase with the flux. The 

 secondary e.m.f. OBz is exactly opposite 

 the primary in phase and its value is 

 equal to that of the primary times the in- 

 verse ratio of the turns of the two wind- 

 ings. 



Suppose now that the transformer is 

 loaded, in which case a secondary current 

 OAi will flow, proportional to the load. 

 If the load was non-inductive this current 

 would be in phase with the secondary 

 terminal e.m.f. OZ>2, thus lagging behind 

 the induced e.m.f. 0#2, due to the leak- 

 age reactance. In this particular case how- 

 ever, the load is inductive and the current 

 6M.2 lagsibehind the terminal e.m.f. OZ>2< 

 degrees, the corresponding power factor of 

 the load being cos (/>. The secondary ter- 

 minal e.m.f. OI>2 is less than the induced 

 e.m.f. OE$2 on account of the resistance 

 drop 8^2 and the reactance drop CzDi- 

 These values are the product of the secondary current times the 

 resistance and the reactance, respectively, of the secondary wind- 

 ing, the former being in phase with the current and the latter in 

 quadrature. 



When the secondary current flows it disturbs the equilibrium 

 by tending to demagnetize the core, and the primary current 

 increase until, in addition to -the exciting current OM\, a current 

 flows, the magnetizing effect of which just balances the magnet- 

 izing effect of the secondary current. This additional current- 

 is represented by M\A\ and it is just equal and opposite to the 

 secondary current OA 2 times the inverse ratio of the number of 

 turns in the windings. 



The total primary current OA\ is, therefore, seen to be com- 



FIG. 224. Theoretical 

 Transformer Diagram. 



