DIRECT-CURRENT DYNAMOS AND MOTORS. 59 
Flux per pole, formula (21): 
po — 8X 10° x 550 
~ (90 X 4) xX 4.0 
= 22,971,000 lines; 
Cross-section of body: 1.8 X 93 X 25 = 438 sq. ins.; 
Cross-section at roots of teeth opposite one pole : 
41x xzw— 90 x 
4 
xX .9 XK 25 = 277 sq. ins.; 
Flux density in armature body: 
22,917,000 + 438 = 52,300 lines per square inch; 
Flux density in teeth: 
22,917,000 + 277 = 83,000 lines per square inch; 
Hysteresis factor for body (Table 19): 7 = .0103; 
_ Hysteresis factor for teeth (Table 19): 7 = .0215; 
»*» Power loss by hysteresis: 
Wy = .0103 X 13.33 X 21,537 + .0215 X 13.33 XK 2,400 
= 2,960 + 690 = 3,650 watts. 
Fic. 19.—DIMENSIONS OF 330 K W. TootrHEeD RING ARMATURE. 
Supposing the iron used in this armature is .0/5 inch 
thick. Since the eddy current loss is proportional to the 
square of the thickness, and since .015’,= 3 X .010’, we 
must multiply the factor found in Table 20 for .010’ 
iron at the given flux density by ($)’, or by ?. The eddy 
current factor for 52,300 lines and .010” iron is .000012; 
hence, for .015” iron, ¢ = .000012 x # = .000027, Sim- 
ilarly for 83,000 lines (density in teeth), ¢ =.000030 x ~ 
=.000068, 
