282 



ELEMENTS OF ELECTRICAL ENGINEERING. 



represent speed of rotor in per cent, of synchronous speed, and 

 the ordinates represent power output in kilo-watts and torque in 



.300 



100- 



300 



O 100 200 



rotor speed (n = 100) 

 Fig. 244. 



kilogram-meters, in this case, however, the calculations are ex- 

 tended above synchronous speed, where n f > n ; and below stand- 

 still, where n' is negative. 



137. Determination of the circle diagram by calculation from the details of 

 design of an induction motor. In order to determine the circle diagram it is neces- 

 sary to determine the phase and value of the magnetizing current, M, in each stator 

 winding, and to determine the diameter of the circular current-locus. By referring 

 to Arts. 1 20 and 121 it will be seen that the diameter of the circular current-locus 

 is the current which would flow through each stator winding (the primary coil) if the 

 resistance in the main circuit shown in Fig. 216 or in Fig. 251 were zero and only the 

 reactance X due to magnetic leakage were left. That is, the diameter of the circu- 

 lar locus is equal to E' J X, and to determine it one must calculate the value of the 

 magnetic leakage reactance X of the stator windings per phase. When the circular 

 current-locus has been determined, it is necessary to know the value of the resistance 

 R f of each stator winding and the equivalent resistance R f/ of the rotor per stator 

 phase, before the circle diagram can be used for calculating the performance curves 

 of the motor. 



Calculation of magnetizing current per phase. The calculation of the mag- 

 netizing current per phase consists of three steps, namely, (a) The calculation of total 



