30 THE DESIGN OF STATIC TRANSFORMERS 



TABLE 1. VALUES FOR "VOLTS 1-1:1; Tn;\" IN TI:ANSI--<I:.MKI:S 

 OF LARGE OUTTUTS. 



For our present purpose, let us take for the " volts per turn" 

 of the 20-kw transformer the value read from the curves in Fig. 8, 

 namely, 1,6 volts. There will thus be required (roughly) some 



(-= 7 =j 125 secondary turns, and 3125 primary turns, the 



ratio of transformation being 25. It is generally convenient, in 

 the first place, to adjust the number of secondary turns to a 

 figure which is some multiple of four or else a multiple of some 

 even number greater than four. Consequently we shall take 

 124 secondary turns and (25 X 124 =) 3100 primary turns. 



Let us now turn our attention to the consideration of the 

 fundamental orthodox formula connecting the pressure with 

 the number of turns, the periodicity and the total flux in the 

 core. I consider that the most useful way of expressing this 

 formula when used for transformer design is 



V = 0,0444 T co M 



where V represents the pressure in volts, T the total number 

 of turns in series between the terminals which have a pressure 

 of V volts between them, M the total flux in megalines and co 

 the periodicity of reversal of the pressure, in cycles per second. 

 This formula, however, is only correct for a transformer 

 operated from a circuit in which the pressure wave is a sine 

 curve, and although, in many cases, it is justifiable to make 



