PKOBLEMS 291 



28. A railway generator is being tested by the electrical 

 method described on p. 87. The line tension is 550 volts, 

 the speed is 400 r.p.m., the generator output is 500 amperes, 

 the resistance of the generator is 0-04 ohm, and that of the 

 motor 0'03 ohm. If the current from the line is 48 amperes, 

 and the torque losses are equal in the two machines, find the 

 torque loss in the generator. 782 inch-pounds. 



29. A motor is tested by Hopkinson's method. The 

 total mechanical output is 45 horse-power when running 

 at 900 r.p.m. on a tension of 125 volts. The resistance of 

 the motor and of the generator used in the test are both 

 equal to 0'015 ohm. The torque input measured on the 

 belt is 600 inch-pounds. What is the torque loss in the 

 motor? 191 inch-pounds. 



30. A generator is being tested by the method described 

 on p. 87. The terminal tension is 250 volts, the current 

 output 800 amperes, and the current from the line 92 am- 

 peres. The resistance of each armature is 0-0058 ohm. If 

 the power used in magnetising the magnets of the generator 

 is 5-2 k.w., find its total efficiency. 92-5 per cent. 



31. A railway motor is tested by the method described on 

 p. 144. The terminal tension on the motor is 500 volts, the 

 current 44 amperes, the resistance of the motor magnets and 

 armature 0'72 ohm. The generator current is 34 amperes, 

 and the resistance of the generator magnets in series with 

 the motor circuit 0-43 ohm. Find the efficiency of the 

 motor. 83 per cent. 



32. A motor generator runs at 550 r.p.m. on a tension of 

 588 volts. The current in the motor is 64 amperes, and that 

 in the generator 280 amperes. The motor resistance is 

 0-175 ohm. The induction factor of the motor is five times 

 that of the generator. Find the total frictional losses in the 

 two machines. 705 inch-pounds. 



33. A motor has an induction factor equal to 6, an internal 

 resistance of 0-08 ohm, and torque losses amounting to 76 



u'2 



