Alternate Current Transformer. 



67 



If s/I/QK=:l, max. T would be the same for both types, and if 

 2^I/QK<1, the shell type would be the better. 



Magnetic leakage is in general less, and good regulation more 

 easy to attain in core transformers than in shell transformers. 

 To enable a comparison to be made with the shell transformer in 

 the last paragraph, we will determine the sum of the leakage 

 coefficients and the regulation for different kinds of load of the 

 core transformer considered above, supposing it to be wound 

 (rt) in thi'ee layers, one primary and two secondary or vice versa ; 

 (h) in five layers, two primary and three secondary or vice versa. 



From § 54, 



1 2^ ^ 

 ij 3/.X'2 QK' 



and A=4(^ + // + 2^). A' = 45', so that, using the same values for 

 the constants as before, we find, 



for (a) A-i + .T2 = . 000381, 

 (h) a"i+X2 = .000127, 

 from which, proceeding as in § 52, we find for the regulation 



A'l + X^ 



58. It is obvious that in core transformers of the ring type 

 in which the winding is continuous all round, the maximum 

 efficiency shape will, other things being equal, be that in which 

 the magnetic circuit is shortest, that is when the opening in the 

 laminae is filled with the copper circuits. The ring type is not 

 suitable for practical construction, but a near approach to it is 

 the Burnand transformer,* in which the magnetic circuit is 

 formed of square laminae from which a symmetrically placed inner 

 square has been removed to give the winding space. Each side 

 of the square is built and wound separately with triangular 



'See "Electrician," Sept. 19, 1902. 



