42 ELECTRICAL ENGINEERING PROBLEMS 



an active conductor length of 33 cm. The mean density in the 

 slots is 3600. With how many pounds does the conductor press 

 against the side of the slot? If the area of the air gap is 1360 

 sq. cm. and the total flux is 15.5 megamaxwells, what would be 

 the pull on the conductor if the armature were smooth core? 

 (4 ram.) 



22. A 220-volt shunt motor is to be used as a dynamometer to 

 measure the power taken by a lathe making a heavy cut. The 

 speed is 1060, the current is 23.2, and the voltage on the armature 

 is 218. With 218 volts on the field and 209 on the armature it runs 

 without load at 1060 r.p.m. and takes 1.7 amperes. The resistance 

 of the armature is 0.62 ohm. Required the power taken by the 

 lathe. (5 rain.) 



23. Two 10-h.p., 1200-r.p.m., 220-volt motors are mechanically 

 coupled and have their armatures connected in series on a 220-volt 

 circuit. The fields are each normally excited. At what speed will 

 the motors run, and how many horse-power will the combination 

 produce? (2 ram.) 



24. Same as problem 23, except that one motor is a 220-volt 

 and the other a 110-volt motor. (3 ram.) 



25. Same as problem 23, except that the field strength of one 

 motor is increased 25%. (4 ram.) 



26. A 4-pole, 2-path, 500-volt series motor has a full-load 

 rating of 20 amperes. The armature and field resistances are 

 1 and 1.4 ohms and there are 920 conductors. The field turns per 

 pair of poles are 300. Its magnetization curve is as follows: 



Ampere-turns . . . 3000 4000 5000 6000 7000 8000 9000 

 Megamaxwells .. 1.76 2.27 2.72 3.02 3.14 3.25 3.34 



Required the speed for half load, full load and 50% over load. 

 The brushes are midway between the pole tips. (6 ram.) 



27. If a resistance of 10 ohms is put in series with the motor 

 of problem 26, at what speeds will it run with full-load current and 

 with half-load current? (3 ram.) 



28. If a shunt of 1.4 ohms is put around the field in problem 26, 

 at what speed will it run when taking 20 amperes in the armature? 

 (2 ram.) 



29. Given a 4-pole, 500-volt, 35-h.p. railway motor with a 

 2-path winding, 44 field turns per pole, 744 armature conductors, 

 armature resistance 0.32 and field resistance 0.168. The brushes 



