THE TRANSFORMER 295 



output = 110X10 = 1100 watts. By reference to the "total 

 loss " curve we see that the losses in the transformer for 10 

 amperes output amount to 80 watts. 



Hence the efficiency of this output = -^ = 93.3% 



llUU~{~oU 



2200 

 At 20 amperes output the efficiency = ^ ^ =96.0% 



At 



" " 





3300+120 



. 

 At 40 " " " = _ __ _ QA7C7 



4400+153"" 

 55QC 



5500+195- - 



Form of Efficiency Curve. The efficiency curve is, thus 

 predetermined and has the shape given in Fig. 186. 

 This method of calculating efficiency is not rigidly correct 

 because the secondary voltage does not remain quite con- 

 stant as we have assumed. The resulting error is, however, 

 practically negligible. 



Power Factor Curve. The power factor curve of the 

 primary circuit (supposing a non-inductive secondary 

 load) has the shape given in Fig. 186. The power factor is 

 about .30-.40 at no load and quickly rises to approximately 

 1.00, maintaining this high value until the transformer is 

 heavily overloaded. 



Decrease in Secondary Terminal Volts as the Load Increases. 

 The secondary voltage falls slightly with an increase of 

 load (a constant impressed primary voltage being assumed), 

 the total change from no load to full load being 2-5%, 

 expressed as a percentage of the full-load voltage. This 

 percentage is called the regulation of the transformer. 

 Its value depends upon the resistance of the windings and the 



