THE INDUCTION MOTOR. 



357 



power exerted 



Consequently the efficiency = 



J J power supplied to motor 



C e e v l slip . . 



= f^ =-=,=- - m accordance with the notation 



Li tii tii V 



employed above. By exactly similar reasoning the 

 power lost in the alternating-current armature is N &r 



speed of rotor v 1 - slip 



and the efficiency is 



synchronous speed 



Making use of these results and equation (7) we see 

 that for the same losses in the armature the torque, and 

 consequently the power, exerted by the induction motor 

 is I'll times as great as with a direct-current motor, 

 and that the factors upon which the torque and power 

 depend are similar for the two cases. 



The E.M.F. in the rotor conductors increases in 

 direct proportion to the slip. Thus with constant 



s = o 



Slip. 



S = 100 per cent. 



FIG. 177. RELATION BETWEEN SLIP AND TORQUE AND CURRENTS IN MOTOR 

 WITHOUT LEAKAGE. 



field and rotor resistance, the current and the turning 

 effort will increase in the same ratio as the slip, and 

 curves showing the dependence of rotor current and 

 rotor torque upon slip would both be straight lines as 

 shown in Fig. 177. 



Effect of Magnetic Leakage. The leakage occurring in 

 an induction motor is of two kinds, viz., that in the 

 stator and that in the rotor. 



The stator leakage field is formed of magnetic lines 

 which do not enter the rotor, but pass across from tooth 

 to tooth of the stator core without crossing the air gap 



