S-A] 



STUDY AND OPERATION. 



129 



ance or other load, this electromotive force causes a current 

 to flow. 



The condition very nearly attained in the operation of a trans- 

 former is the transference of power from the primary to the 

 secondary without loss, the current and voltage being one in- 



FIG. i. Connections for loading a transformer. 



creased and the other decreased in the ratio of turns. Using 

 subscripts I and 2 to refer to the primary and secondary, respec- 

 tively, the product E 2 I 2 is accordingly nearly equal to EJ^ t 

 being in fact only a few per cent. less. 



As an example, let S = ioS 2 in a 20 K.W. transformer. The 

 condition very nearly attained is 



Primary watts =20,000 Secondary watts =20,000 



Primary volts = 1,000 Secondary volts = 100 



Primary amperes = 20 Secondary amperes = 200 



Orf account of losses, however, if the secondary is to have its 

 full rated watts, volts and amperes, the corresponding primary 

 quantities must be slightly more than the amounts shown above. 



There are, accordingly, the following losses: lost watts; lost 

 volts; lost amperes. 



The lost watts determine the efficiency and are due to core 

 losses (hysteresis and eddy currents) and copper losses in both 

 the primary and secondary windings. 



The lost volts determine the regulation, and are due to resist- 

 ance drop or copper drop (which, for a given load, is propor- 

 tional to copper loss, see 30, Exp. 5-B) and reactance drop due 

 to magnetic leakage. 

 10 



