THE TRANSFORMER 193 



Knowing the equivalent impedance and equivalent resistance, 

 the equivalent reactance is readily found. 



X Q = Vzf- K (60) 



for either primary or secondary side. 



In making the short-circuit and the open-circuit tests, the 

 question of instrument losses should be investigated and correc- 

 tion made if this be found necessary. As the losses in a trans- 

 former are very small, the power taken by the instruments may 

 be a large percentage of the power being measured. 



85. Regulation and Efficiency. The data obtained from the 

 short-circuit and open-circuit tests are sufficient to compute the 

 ilution and the efficiency of the transformer at any load. 



As the equivalent resistance and reactance referred to eiiher 

 side are known, it is merely necessary to proceed by the method 

 of Par. si, page 182, to determine the regulation. The pro- 

 cedure will he demonstrated by an example which follows. 



It has been pointed out that with constant voltage the mutual 

 flux of the transformer is practically constant from no load to full 

 load. It usually does not vary more than from 1 to 3 per cent. 

 Then-fore, the core loss is practically constant at all loads and 

 may be determined by the open-circuit test, Fig. 177. For most 

 purposes it is necessary merely to measure the loss at the rated 

 voltage of the transformer. 



The only other losses are t he primary and secondary copper 

 . These can be calculated readily, knowing the resistances 

 of primary and secondary, or they may be computed from the 

 equivalent resistance determined at short-circuit. The efficiency 

 of the transformer may then be computed, since i he losses are 

 known. That is. the efficiency 



V I IM 



F,/,(P.F.) -f Core Lose >' / ; /,', + /,*#, 



l,/ 1'.! 



V I i> I . Coreioes 





nple. A 20-kv-a., 2,200 tojjo- volt. () il.utinn i 



18 tC8to<i fur flinrnrv ami regulation as foil.. M annm-trr 



< t In- input to tin |..\\ -n|i-. t he liu 



Ix'iiiH lifril as shown in I'm 177 I in VTAttl <ls 148 



watts, the amp. and the voltm. t is. Tin- trans- 



13 



