CHAPTER XIII 

 HEATING AND RATED CAPACITY OF DYNAMOS 



1. If a cylindrical coil 6 inches in diameter and 10 inches long 

 has a resistance of 8 ohms, and a current of 5 amperes is passed 

 through it, what will be the final temperature, if there be radiated 

 0.01 watt per sq. in. per degree F.? (2 min.) 



2. If the coil of a magnet with the same character of surface 

 as above were 4 inches in diameter outside and 5 inches long, how 

 many watts could be allowed ii* the same, if its maximum tem- 

 perature above the atmosphere is to be 80 degrees? Figure only 

 the cylindrical surface as radiating. If operated on a 10-vult 

 battery, what resistance must the coil have? (2 min.) 



3. A rectangular field coil 10 X 16 inches carries a current of 

 10 amperes and has a drop of 40 volts. The surface being such 

 that ?bv wa ^t is given off per sq. cm. and degree centigrade, how 

 long must the coil be, not to have a rise of more than 40 degrees 

 above the temperature of the air? (2 min.) 



4. For an armature of a certain type and speed there are 0.02 

 watt radiated per sq. in. per degree F. (area taken as two com- 

 plete ends and the cylindrical surface). The diameter is 10 inches 

 and the length 8 inches. The resistance is 0.04 ohm, and the 

 hysteresis and eddy loss is 300. What is the temperature rise on a 

 full load of 100 amperes. (2 min.) 



5. The type and speed of a lO^pole, 550-kw., 550-volt generator 

 (90 r.p.m.) are such that a rise of temperature of 85 C. in the 

 armature would dissipate one watt per sq. cm. If the available 

 radiating surface of the armature is 78,500 sq. cm., the resistance 

 0.0125 and the iron loss 11,000 watts, required the temperature 

 at full load. 



What would be the capacity of this machine if rated in accord- 

 ance with the A.I.E.E. standardization report? (4 min.) 



6. A 6-pole, 150-kw., 250-volt generator (same machine as in 

 problem 2, Chap. XII, 450 r.p.m., peripheral velocity 2840 ft. 

 per minute) has an armature surface of such a character that i 

 radiates ^ of a watt per square inch and per degree centigrade 



33 



