80 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



the stator winding between terminals is 0.561 ohm at 25 C. The 

 ohmic resistance of the open-circuited rotor winding between 

 terminals is 0.0766 ohm at 25 C. The leakage reactance of the 

 stator winding is 3.64 ohms between terminals. With the rotor 

 blocked 375 kw. is supplied when the line current is 369 amperes. 

 The temperature of the windings at this time is 25 C. Assume 

 that the ratios of effective resistance to ohmic resistance are the 

 same for the stator and rotor windings at 25 C. 



What is the output for the specified load? What is the slip? 

 What is the distribution of the losses? The temperature at this 

 time is 73 C. 



43. l A 3-phase, 2000-volt, 60-cycle induction motor has a full- 

 load capacity of 500 h.p. The stator winding has an effective 

 resistance of 0.36 ohm and a leakage reactance of 1.1 ohms per 

 phase. The rotor winding has an ohmic resistance of 0.157 ohm 

 and a leakage inductance of 1.96 mil-henry s per phase referred 

 to the stator. Both of the windings are connected in Y. The 

 magnetizing current is 23 amperes, the core loss is 2470 watts, 

 and the friction and windage is 11 kw. 



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

 motor delivers its rated output? The impressed voltage has 

 such a value that the voltage generated in the stator winding by 

 the air-gap flux is 1850 volts. 



44. 1 A 3-phase, 1900-volt, 22.5 cycle, 36-pole induction motor 

 has a full-load capacity of 570 h.p. The ohmic resistances of 

 the stator and rotor windings are 0.488 ohm and 0.0138 ohm per 

 phase, and their effective resistances at the rated frequency are 

 respectively 1.4 and 1.6 times as great. Both of the windings 

 are connected in delta, and the ratio of transformation of stator 

 to rotor is 6 to 1. The magnetizing component of the line cur- 

 rent is 57.2 amperes, the core loss is 2.8 kw., and the friction 

 and windage loss is 12 kw. With the rotor blocked the line 

 current is 200 amperes when the impressed voltage is 600 volts. 

 Assume that the ratios of leakage reactance to effective resistance 

 at the rated frequency are the same for both stator and rotor 

 windings. 



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

 motor delivers its rated output? Assume that the voltage 

 generated in the stator winding by the air-gap flux is 1790 volts. 



^se either the transformer diagram or the equivalent circuit in the 

 solution of this problem. 



