Alternate Current Transformer. 17 



P^^^^(,_2^^^] (see§M5, 18). 



JOSd) '11 i ^ 



and the percentage drop from no load to full ioad in such a case 

 is 



,ooV^»{/-(/-0Vf^} 



which shows that the limit of possible excellence in regulation of 

 a transformer, designed as above and perfectly wound, i.e., 

 having no magnetic leakage, is when the percentage drop from no 

 load to full load is 



lOOv/T^i^ Cos</,. 



It has already been shown that the maximum efficiency of a 

 transformer is 



so that as regards both efficiency and regulation ■-- 



TSinS 



may be taken as the measure of the excellence of a transformer 



when the magnetic leakage or nature of the winding is not 



considered. 



In general, for a transformer with negligible leakage, the 



percentage drop from no load to a load P^ being 



100— -5^ TCosP 



PqCos^ 



as Po = i-^ (q.p.) 



the drop (p.c.) = 200%'^(l + Ii) 



= 400^A^P, (q.p.) 



Reducing to practical units we find that the percentage drop 

 in a transformer cannot be less than 



oAA -D ■ I Output in Watts 



200 X Primary otnns x ^ — 



(Primary virtual volts)'' 



In no practical case is the leakage negligible, but with inter- 

 leaved winding ^ (.-Vj + .^2)'^ will be very small and f^ \~^ ~\^ 



is very small in transformers of 20 K.W. or over, hence for such 

 transformers the drop per cent, from no load to a load P.^ 



