PKOBLEMS 289 



drum has a diameter of 48 inches. The velocity ratio is 70. 

 The tension of the line is 125 volts. The internal resistance 

 of the motor is O'l ohm. Find the number of useful lines 

 per pole. O55 x 10 6 . 



17. A motor has to raise a weight of 1,500 Ibs. at 200 

 f.p.m. The frictional torque is 430 inch-pounds on the motor 

 shaft. The rope drum is 36 inches in diameter. The velocity 

 ratio is 75. The tension is 125 volts, and the resistance of 

 the motor 0-05 ohm. Find M. 4-47. 



18. A tramcar has to be driven at 13 miles an hour by 

 two four-pole motors connected in parallel on a 500-volt 

 line. The armatures are series-connected with 900 surface 

 conductors. The total tractive effort per motor at full speed 

 is to be 800 Ibs. The resistance is 1'3 ohm per motor. The 

 wheels have a diameter of 33 inches. The velocity ratio 

 is 4 - 78. Find the area of each polar surface in square centi- 

 metres if the magnetisation in the gap is fixed at 5,000 lines 

 per square centimetre. 435 sq. cm. 



19. A gearless motor has to exert a total tractive effort of 

 800 Ibs. when running at 12 miles an hour on 33-inch wheels. 

 The tension of the line is 500 volts, and the resistance of the 

 motor 1'5 ohm. Find the induction factor of the motor. 



214. 



20. Find the current taken by the motor in Problem 19. 

 If gearing with v = 4 is introduced, without altering any 

 other conditions, what is the current ? 



43'7 amperes in both cases. 



21. A tramcar is equipped with two motors, each 

 having M 60 and 11 = 1-5 ohm. If E = 500 volts, 

 v 4'8, and d = 83 inches, find the speed in miles an hour 

 (1) in parallel, (2) in series, when the total load per motor is 

 700 Ibs. horizontally. 9-4 and 4-2. 



22. A motor car weighing 60,000 Ibs. is driven by two 

 gearless motors, connected in parallel, at 16 miles an hour 

 on a level. The tension of the line is 500 volts, and the 

 motors take 20 amperes each. The resistance of each motor 



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