62 THE DESIGN OF STATIC TRANSFORMERS 



Let us now stud)' the " annual " efficiency of Transformer B. 



/190 X 8750 X 0,2 

 -The 1* R loss per annum is equal to ( - 



320 kw hr. 



( 



1000 



^ . /360 X 8750 \ 

 The core loss per annum is equal to ( TOOO / 



kw hr. 



rp u . /8750 X 0,20 X 20 000 \ 



The output per annum is equal to ( - ' 



85 000 kw hr. 



Thus the input to the transformer per annum is made up of: 



Core loss 

 Copper loss 

 Output . 



. 3150 kw hr 

 330 

 .35000 



Total input . 38 480 

 "Annual" (or " energy ") efficiency . 91 per cent. 



We have assumed, however, that the load factor on the trans- 

 former is 20 per cent. If similar calculations are made for 

 different load factors for each of these two transformers we 

 obtain the results set forth in Table 6 : 



TABLE 6. "ANNUAL" (OR "ENERGY") EFFICIENCY OF 20-KW 

 TRANSFORMER FOR VARIOUS LOAD FACTORS. 



