THE INDUCTION MOTOR. 



373 



NO-LOAD TEST OF THREE-PHASE INDUCTION MOTOR. 



Motor No Type : Brown-Boveri four-pole. 



Output 2 h.p., at 1,460 revs, per minute. 

 Voltage 200 50 rv. 



Volts Decreasing from Maximum Value. 



234 



121 



25 



8-1 

 3-8 

 6-0 



1450 

 1450 

 1260 



1-2 

 2-3 



6-0 



153 

 359 



878 



Volts Increasing from Minimum Value. 



In Fig. 182 it will be noticed that there are two com- 

 pletely separate curves for each of the quantities plotted 

 one portion to the extreme left of the diagram and 

 another more extended portion to the right. We meet 

 here for the first time with an illustration of the two 

 conditions under which an induction motor will run. It 

 is found in many experiments that under certain con- 

 ditions, the motor will run at either of two speeds, one of 

 these speeds being more stable than the other. In the 

 present case, for instance, at 30 volts (see Fig. 182), the 

 motor would run either at 1,320 revs, per minute, as 

 indicated on the upper curve, or at 110 revs, per minute, 

 shown on the lower curve. Corresponding to either 

 speed is found a set of internal conditions of currents, 

 watts, &c., quite distinct from those existing at the other 

 speed. The external condition, i.e., the nature of the 

 voltage applied, was identical in the two cases. At points 

 where the two sets of curves overlap, the curves cor- 

 responding to the higher speed in all cases represented 

 the more stable conditions, i.e., the motor after running 

 a short time at the lower speed would generally speed up 

 until the conditions of the right-hand curves were reached. 

 The unstable curves are not of much practical value, since 



