STAILED STUDY OF OPERATION WITH NORMAL LOAD 61 



In rectangular co-ordinates the relationship between E 2 and / is 

 presented by the hyperbola 1 passing through the point of inter- 

 tion of the two arcs of the ellipse of zero-power, and having its principal 

 horizontal and situated above the axis of abscissas at a height 

 to 



RE l 

 / 22-- 



The excitation which renders the current a minimum must there- 

 decrease at first when the power required, P 2 , increases; and it 

 ist then increase more and more. The greater the impedance the 

 Dner this increase will occur. These results are confirmed by experi- 



j, but, in practice, this critical value of E 2 may 'be considered con- 

 stant. 



Curve of Reactive Current. Fig. 32 would be incomplete if only 

 the total current / were represented therein, because the diagram would 

 not then give information in regard to the phase of the current. It 

 is therefore quite useful to add, to the V-curves, other curves indicating 

 the value of the corresponding positive or negative reactive current. 

 The values of the reactive current are deduced from the diagram by 

 constructing the lines corresponding to each value of the phase-angle 

 6. The curve of reactive current corresponding to P 2 2o k.w. has 

 been drawn as an example in Fig. 32. In practice this curve can be 

 plotted from measurements made by a wattmeter. 



Expression for Reactive Current. The expressions for currents 

 which are reactive with regard to EI or E 2 can be calculated in like 

 manner. The reactive current as a function of E 2 will be obtained 

 by starting from eq. (tri). This equation can be written 



Thi 



~ + 2P 2 R + 2E 2 XI d . 



(7 T> 

 ^ 

 -C.2 



is is also an equation of the 4th degree in E 2 , but it can be easily 



Ived with respect to I d , if written in the following form: 

 /7PA2 

 1 The conditions of zero phase-angle of the current with respect to the E.M.F. 

 2 would be the same on an ellipse such as 



7? 2 Z7 2 I /" *7 J\\ 

 & l ' = & +(!)' 



but they present no special interest. 





