GENERAL THEORY OF THE INDUCTION MOTOR. 279 



the magnetizing current so determined, and we have one point M 

 on the circular locus of the stator current (per phase). 



Another point on the circle may be determined by measuring 

 the stator current and the power delivered (per phase) at any 

 load or at standstill. Thus, if the stator current per phase and 

 power per phase be measured at standstill, the line OP repre- 

 senting the stator current per phase at standstill may be laid off 

 in the same way as the line OM, as above explained. 



Knowing the two points M and P on the circle, and know- 

 ing that the diameter of the circle is a line passing through M at 



Fig. 242. 



right angles to OE , aline P' P" may be drawn through P f at 

 right angles to MP f , and thus the diameter MP" of the circle 

 is determined. The circle may then be drawn. 



In order to use the circle diagram for calculating the perform- 

 ance curves of an induction motor it is necessary to measure the 

 resistance R f of each phase of the stator winding and to determine 

 what is called the equivalent resistance R" of the rotor per stator 

 phase. If the rotor were wire-wound with the same number of 

 conductors per phase as the stator winding, then R" would be 

 the actual resistance of each phase of the rotor winding ; in this 

 case the current in each rotor phase would be equal to the load 

 current I' in each stator phase and the rotor Rl 2 losses would 

 be qR" I n y q being the number of phases. The equivalent rotor 



