CHAPTER XXII 



EFFICIENCY REGULATION, AND SPECIAL 

 TESTS ON TRANSFORMERS 



Efficiency Tests 



The efficiency of a transformer is the ratio of its net 

 power output to its gross power input, the output being 

 delivered to a non-inductive circuit. The power input 

 includes the output together with the losses, which are 

 as follows: (1) The core loss, which is determined by 

 the core loss test at rated frequency and voltage, and (2) 

 the I^R loss of the primary and the secondary calculated 

 from their resistances. As the losses in the transformer 

 are affected by temperature and the wave form of the 

 e.m.f., the efficiency can be accurately specified only by 

 reference to some definite temperature, such as 25 deg. C. 

 and by stating whether the e.m.f. wave is sinusoidal or 

 otherwise. The formula for efficiency may be written 



Per cent efficiency = 



output + core loss-f-/ 2 7? loss 



Regulation Tests 



In constant potential transformers, the regulation 

 is the ratio of the rise of secondary terminal voltage from 

 rated non-inductive load to no load (at constant primary 

 impressed terminal voltage) to the secondary terminal 

 voltage at rated load. Regulation may be determined 

 by loading the transformer, and observing the rise in 

 the secondary voltage when the load is thrown off. This 

 method is not satisfactory on account of the expense 

 of making the test, and the small difference between 

 no load and full load secondary voltages. Much greater 

 reliance can be placed on results calculated from separate 

 measurements of impedance drop, and resistance drop, 

 than on the actual measurement of increase in secondary 

 voltage. 



[190] 



