THE TRANSFORMER 



155 



and the consequent voltage produced, but will not affect the 

 flux and back voltage of the primary. 



The lines which penetrate either winding without affecting 

 the other are called the leakage field. There may- be thus in a 

 transformer both primary and secondary leakage fields. 



The effect of the primary leakage field is to increase 

 uselessly the number of lines to be produced, exactly as if an 

 inductive resistance had been put in series with the winding. 



The effect of the secondary leakage field (which, of course, 

 only occurs when there is a secondary current) is that the 

 secondary current has to overcome the back electromotive 

 force produced by the alternating flux thus set up, which is 

 not counteracted by the primary flux, like the other lines 

 formed by the secondary current. In this case also the 

 result is similar to that of an inductive coil put in series with 

 the winding. 



In either case the result of magnetic leakage is to reduce the 

 useful effect of the voltage of the winding in which it occurs, 

 and to produce the result of an added self-induction in the 

 coil. Leakage consequently produces a lag in the current 

 of the secondary circuit, and increases the lag of the current 

 in the primary. 



It is an important fact that the magnetic leakage increases 

 with the load on the transformer. In order to explain the 

 reason of this Fig. 71 is drawn to represent the primary and 



FIG. 71. DIAGRAM SHOWING LEAKAGE IN TRANSFORMER. 



secondary coils of a transformer wound in a way to produce 

 considerable leakage. At no load, . the primary receives 

 magnetising current and produces an alternating field most of 

 which will follow the magnetic circuit of the iron core because 

 this path has the least reluctance or magnetic resistance. 



