lS 4 TRANSFORMERS. [Exp. 



The secondary terminal voltage, E 2 , is a little (perhaps one 

 per cent.) less than E$ on account of reactance drop X 2 I 2 , and 

 resistance drop R 2 I 2 , the former in quadrature and the latter 

 in phase with 7 2 . For a non-inductive load, the secondary cur- 

 rent, 7 2 , is in phase with the terminal voltage, E 2 . (For an 

 inductive load, 7 2 would lag behind E 2 by an angle 6, where cos 6 

 is the power factor of the load.) 



13. In the secondary, it is seen that ES is constant (flux being 

 constant) and the secondary may, accordingly, be treated as 

 a simple constant potential circuit. The locus of the secondary 

 current, as the load resistance varies, is, accordingly, the arc of 

 a circle, as in any constant-potential circuit with constant react- 

 ance. (See Exp. 4-B.) 



14. Primary Quantities. It has been seen that on open cir- 

 cuit the primary current assumes a certain value 7 , so as to 

 produce a flux that generates a counter-electromotive force just 

 equal and opposite to the impressed electromotive force. When 

 a secondary current 7 2 flows, it disturbs this equilibrium by 

 tending to demagnetize the core. This allows more current to 

 flow in the primary. The primary current increases until (in 

 addition to 7 ) a current 7 (2) flows in the primary, the magnet- 

 izing effect of which (ampere turns) just balances the magnet- 

 izing effect of the current 7 2 in the secondary. The magnet- 

 izing effect of the secondary being thus neutralized, the flux has 

 the same constant value as before (as though produced by 7 

 alone), so that the counter-electromotive force produced by the 

 flux continues to be just equal and opposite to the impressed elec- 

 tromotive force. 



In Fig. 3, the total primary current 7 lf is seen to be composed 

 of the constant 7 (which is small) and the load current 7 (2) , 

 which is opposite to the current 7 2 in the secondary and equal 

 to 7 2 multiplied by (S 2 ^-S 1 ). In a i:.i transformer, the pri- 

 mary load current 7 (2) is equal to the secondary current 7 2 . 



