INDUCTION MOTORS 81 



45. l A 3-phase, 500-volt, 38-cycle, 6-pole railway induction 

 motor has a full-load capactiy of 120 h.p. The ohmic resistances 

 of the stator and rotor windings are 0.04 and 0.01 ohm per phase, 

 and their effective resistances at the rated frequency are respec- 

 tively 1.45 and 1.60 times as great. Both of the windings are 

 connected in Y, and their ratio of transformation is 2 to 1. The 

 magnetizing component of the line current is 34 amperes, and 

 the total no-load losses are 4400 watts. With the rotor blo< -k< ! 

 the line current is 800 amperes when the impressed voltage is 500 

 volts. Assume that the leakage reactances of the stator and rotor 

 windings at the rated frequency are equal when reduced to tho 

 same side. 



What are the slip, the power factor and the efficiency when 

 the motor delivers a torque of 1200 pound-feet? Assume that 

 the voltage generated in the stator winding by the air-gap flux is 

 475 volts. 



46. l The full-load capacity of a 3-phase, 2000-volt, 50-cycle 

 induction motor is 335 h.p. The motor is wound for 6 poles, 

 and both the stator and rotor windings are connected in V. 

 The effective resistance of the stator winding is 0.23 ohm and t he 

 ohmic resistance of the rotor winding referred to the stator is 

 0.203 ohm per phase. At 50 cycles the leakage reactances of tho 

 windings, referred to the stator, are respectively 0.70 ohm and 

 0.83 ohm per phase. At no load the motor takes 15.2 ampen- 

 from a 2000-volt circuit at a power factor of 0. 187. The core loss 

 is 7400 watts at this time. The motor is operating with a slip of 

 1.43 per cent., and the terminal voltage has such a value that 

 the voltage generated in the stator winding is the same as at 

 no load. What is the output of the motor? What is the power 

 factor'.' What is the efficiency? 



47. ' A 3-phase, 500-volt, 38-cycle railway induction motor ha- 

 a full-load capacity of 150 h.p. The ohmic resistances of the 

 stator and rotor windings are 0.052 ohm and 0.013 ohm per pha-e. 

 and the effective resistances are respectively 1.40 and 1.55 time- 

 as great at the rated frequency. The motor is wound for 8 pole-. 

 Both -stator and rotor windings are connected in V and have a 

 ratio of transformation of 9 to 5. At no load with an impi -d 

 voltage of 500 volts the motor takes a current of 46.6 amperes at 

 a power factor of 0.141. With the rotor blocked the motor take- 



1 Uso either tin- tr.'iMsfnrnuT diagram or the equhralenl rii-mit in tlu- 



solution of this prot.lrm 



