16 ELECTRICAL ENGINEERING PROBLEMS 



necessary; also on a 110- volt circuit, the area and the B. & S. size of 

 wire, if the mean length of turn is 12 inches, resistivity 12 and if 1000 

 circular mils per ampere be used; also the current and number of 

 turns. (6 min.) 



9. A 1-kw., 2-pole, 110- volt generator (1800 r.p.m.) has the 

 following data for its magnetic circuit: Length of two air gaps, 

 0.6 cm.; density, 4400; length in armature, 13 cm.; density, 

 10,000; length in cast-iron field magnet, 80 cm.; area, 200 sq. cm.; 

 total flux in armature, 1 X 10 6 ; leakage coefficient, 1.4; power to 

 excite the field, 12%; mean length of a turn, 24 inches. Required 

 the ampere-turns, size of wire and the number of turns necessary, 

 taking resistivity as 12.5. (5 min.) 



10. Given a round bar 3 inches in diameter, bent into a magnet, 

 and having the length of magnetic circuit 15.75 inches. Find the 

 number of turns necessary to give a pull of 2433 pounds with a 

 current of 5.27 amperes. (10 min.) 



11. Required to design a magnet for use on a 100- volt circuit, 

 and to raise 2000 pounds. Resistivity is 12. Allow 1000 circular 

 mils per ampere. B = 16,000. Use double cotton covered wire 

 (see table, page 104). It is 3J inches between the insides of the 

 shanks of the magnet, which are 4 inches long and are joined by a 

 semicircular yoke; allow J mm. air gap for the roughness of the 

 iron piece to be raised, and 1 inch for the thickness of the winding. 

 Find the diameter of the bar, area and B. & S. number of the 

 wire, the number of turns and the current. (30 min.) 



12. Design a magnet for use on a 110-volt circuit, to raise 2f 

 tons with a factor of safety of 1 J. Length of the magnetic circuit 

 in iron, 50 cm., and in air at joints, ^ cm. Allow 1000 circular 

 mils per ampere; the winding is 1 cm. deep; use cast steel with 

 16 kilogausses, and take the resistivity as 12. Required the 

 number of ampere-turns necessary for the iron; the number of 

 ampere-turns necessary for the air; diameter of the iron; and the 

 area, size and total number of turns of wire. (25 min.) 



13. A 440-kw., 10-pole, 500- volt (at no load), 85-r.p.m. genera- 

 tor has the following data for its magnetic circuit: Cast-iron 

 yoke (T^ of the ring), 130 cm. in length with a density, 7500; 

 laminated cores, 45 cm. each in length with a density, 13,500; 

 armature body (^ of the ring), 85 cm. in length; with a density, 

 9000; teeth, 4.5 cm. in length; with a density, 19,000; air gaps, 

 0.50 cm. in length; with a density, 16,000. The mean length of 





