GENERAL THEORY OF THE INDUCTION MOTOR. 293 



the point P in Fig. 252, the motor torque may be calculated 

 from equation (v), and the motor speed is known directly from 

 the value of s. 



If it is desired to find the power factor of the motor, the total 

 power input, and the efficiency for the chosen position of the 

 point Pj Fig. 252, proceed as follows : Lay off the value of /' 

 along the line OA, lay off the magnetizing current (= OA' 

 divided by Vr* -f- xf) along the line OM, and find the result- 

 ant of the two. The cosine of the angle between OP and this 

 resultant current is the power factor of the motor, the product 

 of this resultant current by OP and by the power factor gives 

 the power intake of the motor per phase, and the power output 

 divided by the total power intake gives .the efficiency. 



Fig. 7.53. Fig. 253*. 



139. The single-phase induction motor. The internal action 

 of the single-phase induction motor is very different from the 

 internal action of the polyphase induction motor, and it will be 

 described first on the basis of an ideal motor in which the resist- 

 ance of the stator winding, the magnetic reluctance of iron and air 

 gaps, and magnetic leakage are all negligibly small, and then 

 these various things will be taken account of in applying the 

 circle diagram to the single- phase machine. Briefly described, 

 the action of the single-phase induction motor is as follows : R' 



