78 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



in order that the starting torque with full impressed voltage may 

 have its maximum value? What is this torque? What is the 

 starting current for this condition and how does it compare with 

 the full-load current? 



34. The ohmic resistances of the stator and rotor windings 

 of a 150-h.p., 3-phase railway induction motor are 0.054 ohm and 

 0.014 ohm per phase, and the effective resistances at the rated 

 frequency are respectively 1.45 and 1.65 times as great. The 

 leakage reactances at the rated frequency are respectively 0.24 

 ohm and 0.071 ohm per phase. The motor is wound for 6 poles 

 and an impressed voltage of 500 volts at 38 cycles. The ratio of 

 transformation from stator to rotor winding is 15 to 7, and 

 both windings are connected in Y. With full impressed voltage 

 the measured slip for a brake torque of 1470 pound-feet is 2.26 

 per cent. 



What resistance should be inserted in each phase of the rotor 

 winding so that the starting torque with full impressed voltage 

 will have its maximum value? What is this torque? 



INDUCTION MOTOR DATA 



35. Draw the Heyland diagram for motor No. A. (a) What 

 are the full-load power factor, slip and efficiency, (b) What is 



