58 THE DESIGN OF STATIC TRANSFORMERS 



virtue of its symmetrical nature, 

 provides an air duct between 

 the core and the inside of the 

 coil. This duct is included in 

 the window section, and leads to 

 the low space factors indicated 

 in Fig. 35. 



From Fig. 34 we find that 

 /a space factor of about 0,37 

 may be obtained in a design 

 such as that with which we 

 are dealing. This value will 

 afford a sufficient guide to 

 obtaining the total cross- 

 section of the winding window. 

 Thus the total required area 

 will be some 



161 

 0,37 



= 435 sq cm, 



We have already determined 

 the width of the winding space 

 to be about 8,5 cm, and there- 

 fore the length of the winding 

 space may be estimated at 



435 



8,5 



= 51 cm. 



I- 1 [<;. :5(;. Sketch of core for a 20-kw 

 5000/200-Yolt 50-cycle transformer. 



The core as thus determined 

 upon is drawn in Fig. 36. 



