ALTERNATORS. 



209 



It was'' desired to obtain magnetisation curves for the 

 three power factors -9, -8, and -7, the current being in all 

 cases 20 amperes, as it was in the curve for non-inductive 

 load. 



From an inspection of the non-inductive curve it was con- 

 sidered that readings taken at voltages of about 100, 90, 

 80, 70, and 60 would be sufficient to enable the curves to 

 be plotted. A preliminary curve was accordingly taken 

 at each of these voltages in the following manner. 



The alternator was connected to a circuit composed 

 partly of non-inductive resistances and partly of an 

 inductive resistance wound upon a magnetic circuit with a 



vo 



O -2 -4 -6 -8 1-O 1-2 1-4 V6 1'8 2'O 2'2 2'4 

 Amperes, excitation 



FIG. 96. CURVES SHOWING VARIATION OF EXCITATION WITH POWER FACTOR. 



variable air gap. (It will in some cases be found most con- 

 venient to connect the inductive and non-inductive resistances 

 in parallel and in other cases in series.) 



The inductive resistance was then given its maximum 

 value, and the non-inductive part of the circuit was adjusted 

 to give the correct current of 20 amperes. The excitation 

 was then adjusted until the voltage had assumed each of the 

 five values, 98, 90, 80, 70, and 60. 



