GENERAL THEORY OF THE TRANSFORMER. 237 



that is when the angle 6 is zero, then R' P and R" I" are parallel 

 to Oa and Ob respectively. In this case Oa is equal numer- 

 ically to E' RT, and E" is equal numerically to Ob R" I" . 

 That is, coil resistances have their greatest effect in causing the 

 secondary terminal voltage of a loaded transformer to fall below 

 the ideal value (E n E' x N" / N f ) when the secondary receiv- 

 ing circuit has unit power factor. 



When the secondary receiving circuit has a very low power 

 factor, that is, when the angle 0, Fig. 202, is nearly 90, then 

 R'f and R"I" are nearly at right angles to Oa and Ob re- 

 spectively. In this case Oa is very nearly equal, numerically, 

 to f , and Ob is very nearly equal, numerically, to ", so 

 that the ratio E' JE" is nearly equal to the ideal value 

 N'jN". 



Transformer regulation is mainly dependent upon coil resist- 

 ances when the receiving circuit is non-inductive, inasmuch as we 

 shall find that magnetic leakage has little effect on the voltage re- 

 lation in this case. On the other hand, when the angle 6, Fig. 

 202, is nearly 90, the regulation is not greatly affected by coil 

 resistances. 



117. Effect of magnetic leakage. It is shown in the next 

 article that a transformer having magnetic leakage (but of course 

 ideal in other respects) is equivalent to an ideal transformer with 

 a certain outside inductance, P, connected in series with its 

 primary coil This inductance is called the leakage inductance 

 of the transformer, and the reactance value coP of this inductance 

 is called the leakage reactance of the transformer. 



The clock diagrams, Figs. 203 and 204, show the general effect 

 (greatly exaggerated) of the magnetic leakage of a transformer. 

 The various lines have the same significance as in Fig. 202, ex- 

 cept, of course, the line a>PI f , which represents the part of E f 

 which is lost in overcoming the leakage reactance. The line 

 toPf is 90 ahead of /' in phase. It is to be noted that the 

 entire magnetic leakage is equivalent to the inductance P in the 

 primary circuit, so that the secondary coil is to be considered as 



