GENERAL THEORY OF THE TRANSFORMER. 



245 



(i). Therefore substituting the value of <' + 3>" + <'" from 

 equations (iii), (iv) and (v) for / -f s in equation (i) we have 



V, Y i 



LT + T + ^J 



(29) 



Some leakage flux passes between the transformer coils where 

 they project beyond the shell-type iron core. This leakage flux 

 has a longer air-path than /, say three times /. Therefore for 

 X we should take the total length of the coils lessened by, say, 

 y$ of the length which is beyond the core. 



Fig. 211. 



Equation (29) expresses the leakage inductance in centimeters, 

 and the right-hand member of this equation must be divided by 

 io 9 to give P in henrys, all dimensions being in centimeters. 



When the primary and secondary coils are wound in sections 

 and interleaved, equation (29) must be modified accordingly. 

 Thus Fig. 210 shows the primary coil placed between two 

 halves of the secondary. In this case equation (29) becomes 



<KN n \\X' Y' 



p = LT + T 



The dimensions X', Y' and g 1 are shown in Fig. 211, \ being 

 the length of the coils lessened by, say, ^ of the length of the 

 portions which project beyond the core. 



