Alternate Current Transformer. 21 



Hi + H, ,,^ / 32 1 , 138v 



from which we deduce for the transformer in question tliat the 

 copper losses are 



= 167 watts at full load 



= 94 watts at ^ load 



= 42 watts at ^ load 



= 10 watts at ^ load. 



The iron loss being 138 watts we find that the efficiency at 

 full load is 97.04 per cent., 



that at f load is 97.02 „ „ 

 ,, ,, ^ load is 96.54 ,, ,, 

 „ ,, I load is 94.40 „ „ 

 which figures, when compared with those in the maker's specifi- 

 cation given above, show a very remarkable agreement. 



Thus we have been able to deduce with considerable accuracy 

 from two observations of the regulation for different power 

 factors, and the observed iron loss, the other details of the 

 transformer given by the manufacturer. 



If we assume 8 = 50° which would mean that the power factor 

 on open secondai-y was equal to SinS or .766, and take Ti = t.2 then 

 Ti = 6930 for this 10 K.W. 60 period ti'ansformer ; eiud Xj^ + x^ = 

 .0004. 



24. As a second illustration of the agreement between the 

 foregoing theory and practice I will consider the X'ecord of a test 

 of a Westinghouse transformer, published in Fleming's "Alternate 

 Current Transformer," vol. i., pp. 564, 569. 



From the no-load readings of Cj, Pj, and E,2 we can determine 

 as has been explained (t5§ 7, 19, 22) tj, SinS, njfi^ and t^, while 

 the voltage drop for any load enables us to find x^ + x^ when Ti, T2 

 and SinS are known (§ 22). 



These constants together with r-^, r,-, and the primary voltage 

 enable us to calculate all the variable quantities connected with 

 the transformer for any load. This has been done for the above 

 transformer tested by Fleming, and the calculated values of 

 Cj, C2, Pj, r/, and Cosa for each output in his test ai'e given in 

 Table I. in parallel columns with the values experimentally 

 obtained by him for these quantities. 



