358 



THE INDUCTION MOTOR. 



between stator and rotor, and so do not affect the rotor 

 conductors. 



Similarly the rotor leakage lines are formed in the 

 rotor core and do not pass into the stator. 



The leakage field consists of the magnetic lines 

 which do not form part of the rotating field. The 

 leakage in either stator or rotor is increased by making 

 the slots nearly or entirely closed, since it then becomes 

 relatively easier for the lines to pass from tooth to tooth 

 in the same core rather than to pass twice across the air 

 gap into the opposite core. The path of the leakage 

 lines is illustrated in Fig. 178. 



The effect of the stator leakage is that a certain 

 number of the lines formed by the stator current have 



FIG. 178. LEAKAGE LINES IN STATOR AND ROTOR. 



no effect upon the rotor, and that a portion of the applied 

 voltage is opposed by the back E.M.F. set up by this 

 portion of the field. In other words, the leakage field 

 of the stator appears in the form of self-induction of 

 the stator winding. It does not produce any appreciable 

 waste of power, but diminishes the output of the motor, 

 since it practically has the effect of lowering the effective 

 voltage applied to the machine. 



The effect of the magnetic leakage in the rotor is 

 somewhat more complicated. The leakage lines do 

 not pass into the stator, and are consequently not 

 neutralised by the stator field. On the contrary, these 

 lines produce exactly the effect produced by the lines 

 formed in the core of a choking coil when supplied with 

 an alternating current, i.e. v they produce a back E.M.F. 

 of self-induction in the rotor winding, and give rise to 

 an increased apparent resistance in this circuit. 



