TRANSFORMERS 



291 



The exciting current 7 is of the order of 10 per cent of full- 

 load current and the no-load power factor is of the order of 30 

 per cent. 



The alternating flux produced by the magnetizing current 

 links with the secondary winding and induces in it an e.m.f., 



e 2 = n *% 10- 8 volts. 

 at 



no 



FIG. 265. Constant potential transformer. FIG. 266. 



If the frequency is / cycles per second and the flux follows a 

 sine wave of maximum value <$, the instantaneous e.m.f. induced 

 in the secondary is 



e 2 = nz-r($> sin 2 irft) 10~ 8 volts 



= 2 Trfn& cos 2 irft 10~ 8 volts 



= 2 Trfnz sin (2 wft - 90) 1Q- 8 ; . . (272) 

 this is a sine wave of e.m.f. in quadrature behind the flux, of 

 maximum value 



# 2 max = 2irfn<&10- s ..... (273) 

 and effective value 



E 2 = - 



v 2 " 



10-* = 4.44/n 2 <i> 10~ 8 volts. 



The flux also links with the primary winding and induces in it 

 an e.m.f. of instantaneous value 



10~ 8 sin (2 irft - 90), 

 a sine wave of maximum value 



E b max = 27T/ni<i>10- 8 



and effective value 



E b = 4.44/ni$ 10~ 8 volts ..... (274) 



net 



