DIRECT-CURRENT DYNAMCS AND MOTORS. 
For this value of c, Table 22 gives an average of 50° C. 
in the present case of a high-speed machine. 
Taking the mean of the two averages found, we obtain 
3(40 + 50) = 45°C. as the approximate average tem- 
perature rise of the armature. 
The armature here considered is that of a machine in actual 
use. It has a temperature rise of 42° C. when running 
continuously at full load. 
50. Example of Toothed Ring Armature.—It is as- 
sumed that the design of a toothed ring armature 
for a 4-pole 330 K. W. compound-wound railway 
generator for an output of 600 amperes at 550 
volts, when running at a speed of 400 revolutions 
per minute, has resulted in the following data: Exter- 
nal diameter of core, 444 inches; internal diameter, 
214 inches; length, 25 inches; radial depth of solid 
portion, 9% inches; number of slots, 90; width of 
slots, 4 inch; depth of slots,12 inches; winding, 4 
copper strips, + inch by 4 tnch, per slot; armature 
resistance, at 20° C.,.008% ohm. Required to prede- 
termine the approximate rise of the armature temper- 
ature. 
Solution.— 
Warm resistance: 7,’ = 1.16  .0087 = .0101 ohm; 
Total current (Table 18): C = 1.02 x 600 = 612 amps; 
*. Power absorbed by armature winding, formula (28): 
w, = 612? x .0101 = 3,780 watts. 
Frequency, formula (80): f = — xX 2 = 13.383 cycles; 
Diameter at roots of teeth: 444 — (2 x 1%) = 41 inches. 
Mass of body, formula (31): 
= (41 — 93) w x 9% X .9 X 25 = 21,537 cu. in. 
Mass of teeth, Fig. 19: 
[ (443)" z — (41)? 7 —90 x 18 x ¥] X .9 x 25 = 2,400cu. in. ; 
