98 THE DESIGN OF STATIC TRANSFORMERS 



before, but the resistance of the secondary winding would 

 now be 



15 2 X 0,0020 = 0,45 ohm. 



Instead of dealing separately with the resistance of the primary 

 and the resistance of the secondary, we may, for such a 1 : 1 

 transformer, speak of the "resistance of the tninxfonm'r" and 

 say that it is equal to 



0,60 + 0,45 = 1,05 ohm. 



The " resistance drop " in this transformer, when the input is 

 33,3 amperes, is 



1,05 .X 33,3 = 35 volts. 



The 100 volts which we have stated to be necessary to send 

 full-load current into the transformer when the secondary is 

 short-circuited, is made up of two components. One compo- 

 nent is the "resistance drop " of 35 volts, which we have just 

 calculated. The other component is the " reactance drop," 

 and is equal to 



VlOO 2 - 35 2 = 94 volts. 



In the example we have taken, we should say that for a primary 

 current of 33,3 amperes, the "resistance drop" is 



or 



3000 X 10 



and the "reactance drop" is 

 04 



3000 X == ' P 



The resistance drop is simply calculated from the number of 

 turns, the cross-section and the mean length of turn in the 

 primary and secondary windings. Such calculations have 

 already been carried through step by step in Chapter II. 



The reactance drop can only be very roughly estimated. It 

 varies greatly with different types of magnetic circuit, with 

 different proportions of the winding-space and with different 

 arrangements of the winding. 



