282 



INDUCTION MOTORS. 



[Exp. 



10. Scale for Power. In any alternating current circuit, 

 power is always proportional to the power component of current ; 

 thus, in a single-phase circuit, JV EX power component of /; 

 in a 3-phase circuit, W ' = E^/ '3 X power component of /; etc. 



In the induction motor diagram, all components of current in 

 a vertical direction are power components and are, therefore, 

 directly proportional to the corresponding power in watts. 



For example, in Fig. i, the power component of the no-load 



2.3 4 5 



Horse Power Output 



FIG. 2. Characteristic curves of an induction motor. 



current, OB, is directly proportional to the no-load losses in watts. 

 The no-load loss can be computed from OB as follows : 



fF = V3XHne voltage X OB = V3~X 185 X 1.09 



= 321 X 1.09 = 350 watts; 

 or, W = 3 X star voltage XOB= 3 X 107 X i .09 



= 321 X 1.09 = 350 watts. 



II. It will be seen that every ampere in a vertical direction 

 in Fig. i, i. e. y every ampere of power component of current, 

 represents a definite number of watts and this number can be 

 readily determined. We can then calculate watts from the 



