194 TRANSFORMERS. [Exp. 



30. An illustration will make this clear. Let 



Regulation drop = E Q E 2 = 2.9 volts. 

 Per cent, regulation = 2.9 -=- 97 = 2.99 per cent. 

 Total voltage drop E^ E 2 = 3 volts. 

 Per cent, voltage drop =3 -=-100 = 3 per cent.; or 

 = 3 -+- 97 = 3- 1 P er cent - 



31. Regulation drop depends upon the difference between E and 

 E f This drop is due to load current, and does not include any drop 

 due to exciting current, which affects E and E z alike and, practically, 

 does not affect their difference. 



The total voltage drop depends upon the difference between E l and 

 E 2 . This drop is chiefly due to load current, but includes, in addition, 

 a small drop due to exciting current which affects E 2 but not E t and 

 so directly affects their difference. 



32. Computations. To compute regulation drop, we have the 

 problem: Given E 2 , to compute E . 



To compute total voltage drop, we have the problem: Given ,, to 

 compute Ej. 



33- Regulation. For determing regulation, we compute 



E = V^ where 







in-phase drop = /> = . 

 quadrature 



It is seen that exciting current does not enter. The various drops 

 may be expressed either in volts or in per cent. The working details 

 of the method are discussed in 34-43, Exp. 5-B. 



34. Total Voltage Drop. For determining total voltage drop, we 

 compute 



The in-phase drop p, consists principally of RI (3) , but includes the 

 small additional terms RJn and XJu, which are drops caused by the 

 two components of the exciting current flowing through X,, R r 

 Without much error, X lt /? t may be taken as half of X, R. Hence 



