56 DIRECT-CURRENT DYNAMOS AND MOTORS. 
No. 9 B. & S.; resistance (at 20° C.), .105 ohm. Find 
the probable temperature increase. 
TABLE 22. 
TEMPERATURE INCREASE OF ARMATURE CORRESPONDING TO 
DIFFERENT CIRCUMFERENTIAL CURRENT DENSITIES. 
Temperature Increase of Armature. 
Circumferential 
Current Density. High-Speed Dynamos. Low-Speed Dynamos. 
Amps. p. inch. ; 
Centigrade | Fahrenheit | Centigrade. | Fahrenheit. 
50 to, 100 15° to 25° 27° to 45°] 10° to 20° | 18° to 36° 
100 ** 200 20° **= BS 36° 7** 68.1 35-49 SR etree ee 
— 200 ** 300 30° “© 60 1-64" ** 90) Borie 36 **. 68 
300 ** 400 40. ** 60.) 92 308 Oba cee £5. 8" | 98 
400 ** 500 SOS 8 9G OG Te a ee 54 * 81 
500 ** 600 60 “ - 86') 108 “** 144°) 2 ** 06 63 ‘* 90 
600 ** 700 70 * 90/126 *° 162 1.400 “260 te ** 308 
700: ** . 800 80. 100.) 144... ** J8Os) 160: 276 99 ** 326 
800 ** 1000 iia sees 69 **§ 80 '108 ** 144 
Solution.—The warm resistance of this armature can be 
approximately taken as 1.16 X .105 = .122 ohm, see Par. 
39. The shunt current of a 5 K. W. dynamo, accord- 
ing to Table 18, is between 5 and 6 per cent. of the ter- 
minal current; the total current, therefore, in this case is 
about 1.05 x 40 = 42 amperes. Hence, the power 
absorbed in the winding, by formula (28): 
W,, = 42? X .122 = 214 watts. 
The frequency, from (30), is: 
BN a <X 1 = 80 cycles per second. 
60 y p 
The mass is found by ($1): 
M = (5% — 14)7 X 1§ X .9 X 94 = 190 cubic inches. 
