410 THE INDUCTION MOTOR. 



as H moves along the circle according to the value given 

 to A B. 



The torque is consequently proportional to A H x 

 B F, that is to the area of triangle A H F, or since the 

 base is constant, torque <x height of triangle A H F, 

 which oc H J. This is the total torque exerted 

 and includes that spent in overcoming friction, &c. 



In order to separate the torque expended in over- 

 coming the friction of the motor itself from the total 

 torque exerted by the rotor conductors we proceed as 

 follows : 



F represents the no-load magnetising current. 

 There will, however, be an energy component of the 

 no-load current F Kin phase with E. Hence, draw K 

 the total no-load current. The component F K perpen- 

 dicular to F will then represent the energy component 

 spent in overcoming friction losses, &c., and must be sub- 

 tracted from the total torque current H J to give the 

 useful torque on the shaft. Thus all lines H L may be 

 taken to represent the effective torque of the motor, 

 on some scale not yet determined. 



(3) Output of Motor. This is the product of the 

 torque exerted by the rotor shaft and the speed. It 

 would thus be proportional to the line H L, which 

 represents the torque exerted by the rotating field on 

 the rotor (since the speed is practically constant), except 

 for the fact that some of this turning effort is taken up in 

 generating the power spent by the rotor current in heating 

 the rotor conductors. This is practically equivalent to 

 a portion of the rotor flux being spent in overcoming 

 the rotor resistance, and may be taken into account 

 by reducing the rotor flux line H A by a piece H N 

 proportional to the electromotive force spent in over- 

 coming the rotor resistance. Then all such lines as 

 N P perpendicular to a 6 are proportional to the output 

 of the motor. The point N will lie on a circle drawn 

 through the points A N F, and having its centre at some 

 point / on the line g q. This circle may be called the 

 circle of output. 



(4) Slip of Motor. The slip is directly proportional 

 to the rotor current, and inversely proportional to the 

 rotor flux, hence 



H F 



