5-B] 



TEST BY LOSSES. 



165 



cent, impedance drop is also called impedance ratio (13, 

 Exp. 3 -B). 



30. Curves for Copper Losses. Calculate RI^ 2 for ^, J, J, 

 |, i and ij load. Plotted as in Fig. 8, these give the values of 



>ioo 







U on 



100 



95.38 



121.9 



80.3 



41.6 



0.25 



0.5 0.75 



AMPERES, PRIMARY. 



FIG. 8. Losses and efficiency of a 2 K.W. transformer. 



the copper loss, including load losses, for different currents; the 

 curve is a parabola. 



It is seen that the copper loss, in watts, for a given load is pro- 

 portional to the copper drop, in volts. The copper loss, expressed 

 as a per cent, of rated volt-amperes, is equal to the copper drop, 

 expressed as a per cent, of rated volts. 



Per cent, copper loss = Rr i /EI. Per cent, copper drop = 



PART IV. RESULTS. EFFICIENCY AND REGULATION. 



31. Efficiency. Efficiency is equal to output divided by in- 

 put and is readily determined when the losses are known. For 

 a particular frequency and normal voltage, take the value of 

 core loss from the curves already determined, Figs. 3, 4 and 5. 



