INDUCTION MOTOK* 77 



the voltage generated in the stator winding at full load is 94 

 per cent, of the impressed voltage. What is the slip when the 

 motor delivers its rated load? What is the starting torque with 

 600 volts impressed on the motor? 



30. At full load the slip of a 500-h.p., 3-phase induction motor 

 is 1.80 per cent. The motor is wound for 12 poles and an im- 

 pressed voltage of 2200 volts at 25 cycles. When the rotor wind- 

 ing is not short circuited the hot resistance referred to the stator 

 measured between terminals is 0.431 ohm, and the effective 

 resistance is 1.65 times as much. What is the starting torque 

 when the impressed voltage is adjusted so that the rotor cur- 

 rent is twice its full-load value? 



31. At full load the slip of a 1000-h.p., 3-phase induction motor 

 i- 1 72 per cent. The motor is wound for 12 poles and an im- 

 pressed voltage of 2200 volts at 25 cycles. When the rotor wind- 

 ing is not short circuited the hot resistance measured between 

 terminals is 0.0895 ohm, and the effective resistance is 1.6 times 

 as great. The ratio of transformation from stator to rotor is 

 2200 to 1500. The effective resistance and leakage reactance of 

 the stator winding between terminals are 0.195 ohm and 0.59 

 ohm. 



What voltage should be impressed on this motor so that the 

 starting torque will be the same as the full-load torque? What 

 is the starting current for this condition and how does it compare 

 with the full-load current? 



32. In problem 31 what resistance should be inserted in each 

 phase of the rotor winding in order that the starting torque 

 for the rated voltage will be equal to the full-load torque? 

 What is the starting current for this condition and how does 

 it compare with the full-load current ? 



33. The olnnie resistances of the stator and rotor windings of a 

 500-h.p., 3-phase induction motor are 0.24 ohm and 0.0 !">.'{ ohm 

 per phase, and the effe< -t i\ resistances at the rated frequency are 

 respectively 1.5 and !.' times as great. The leakage reactances 

 at the rated frequency are respectively 1.1 ohm- and n.()7.~> ohm 

 per pha-e. 'l'li- motur i- wound for 44 pole- and an improved 

 voltage of 2000 volts at 60 cycles. The -tator ha- 1M 12 indm -t..r- 

 and the rator 660 inductors. Both windings are conn, end in V. 

 At full load the voltage generated in the stator winding !,y the 

 air-gap llux is '.! pet | the impressed voltage. 



What re-i-tance should be inserted in each phase of the rotor 



