2O4 



ELEMENTS OF ELECTRICAL ENGINEERING. 



Approximate equality of input and output of power. The out- 

 put of power by g.n ideal transformer would be exactly equal to 

 the input of power. In an actual transformer the output of power 

 is usually 97 per cent, or more of the power input when the 

 transformer is fully loaded ; that is the RI 2 losses in the coils 

 and the eddy current and hysteresis losses in the core are together 

 usually less than three per cent, of the full-load output of a good 

 transformer. This high efficiency of the actual transformer shows 

 how closely the actual transformer approximates to the ideal 

 transformer in its action. 



99. Particular cases of transformer action. (Harmonic electro- 

 motive forces and currents.) The above discussion is not limited 



* 



JE" 



Fig. 172. Fig. 173. 



to any particular wave-form of electromotive force and current, but 

 in order to show the voltage and current relations of a trans- 

 former in a clock diagram it is necessary to consider the case of 



are at each instant opposite to each other and in the ratio N" \ N f ; and <?' and e'r 

 are at each instant opposite to each other and in the ratio JV'/N". Therefore I' 

 and 7 X/ are opposite or 180 apart in phase, and E' and E f/ are opposite or 180 

 apart in phase. 



