SYNCHRONOUS MOTORS. 



285 



curves tend towards that obtained with normal excitation, 

 it does not reach it for the range of loads shown. 



With excitation 1'8 amps., considerably above the nor- 

 mal, values of the current are obtained which are greater 

 than for any of the other curves, and the curve indicates 

 little tendency to approach that taken abnormal excitation. 



The curves of watts (Fig. 134) show that the difference 

 between the power given to the motor when normally and 

 when under-excited is comparatively slight; indeed, the 



O1 23456789 

 Pull in Ibs. at rim of pulley. 



FIG. 134. VARIATION OF POWER TAKEN BY SYNCHRONOUS MOTOR 



WITH LOAD AT VARIOUS EXCITATIONS. 



Pulley Sin. diameter. 



excitation of I'l amps, shows rather better results than the 

 normal 1'36 at higher loads. The curve for over-excitation 

 indicates a considerable amount of waste power as being 

 supplied. 



The curves in Fig. 135, showing the variation in power- 

 factor, illustrate in a very decided manner the advantage at 

 light load of correct excitation. The power-factor in the 

 curve for T36 amps, excitation is high throughout. With the 



