2 SO 



SYNCHRONOUS MOTORS. 



to drive the motor would, however, be found with any 

 motor, which would be similar in its nature although 

 smaller in extent in the case of a more efficient machine. 

 An increase in armature current necessarily gives rise to 

 increased losses in the conductors, armature core, and 

 pole faces of 'the machine. 



The curve of watts shows very forcibly the importance 

 of choosing the most favourable excitation for the motor, 



11OO 



1000 



9OO 



6 80 

 v 



a. 7OO 



3 



3 600 



flt 



^ 5OO 



400 

 3OO 

 2OO 

 1OO 



' 



i: 



2-O 



2-5 



O -5 1'O 1-5 



Amperes, Excitation. 

 FIG. 131. VARIATION OF WATTS WITH EXCITATION OF SYNCHRONOUS MOTOR. 



I. = Motor running light. 

 II. = Output '38 h.p. 

 III. = ,. -81 h.p. 



since the useful work is the same for all points on the 

 curve, although the power supplied to the motor varies so 

 greatly. 



The shape of the curves obtained in Experiment XLII. 

 depends upon the self-induction of the armature of the 

 motor. If the armature were without self-induction the 

 armature current would be in phase with the resultant 

 voltage and would increase in proportion to it. There 

 would then be only one possible value of the exciting 



