ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 177 
336. 
| 337. 
The double cotton covered wires arranged in 7 layers, fill 
0.51 
out the slot, and produce a space factor of iss 38. 
1.75 
The ratio between the slot depth and width is 
see Fig. 79. 
Thickness of Teeth.—The thickness of the teeth has to 
be determined next. 
The internal periphery of the armature is equal to 47.5 X 3.14 
1 
= 149 inches; the slot pitch o is equal to = = 2.07 inches ; 
the narrowest part of the tooth is 2.07 — 0.75 = 1.32 inches 
and the mean thickness will be found equal to 1.4 inches. 
Pole Pitch and Are.—tThe determination of the effec- 
tive armature length is the next step. 
The number of cycles being 25, we will allow in the first 
approximation a magnetic density in the teeth of 95,000 
lines per square inch, which implies a hysteresis and eddy 
current loss of 3.7 watts per pound of iron, this being 
a good average value. 
To proceed in the indicated manner, we have to fix at first, 
the pole are. Provided that the diameter is 47 inches, the 
jal aE ani = 18.45 inches, and 
assuming a pole are ratio of 0.65, the are length will be 
12 inches. 
pole pitch will be equal to 
Length of Armature.—The number of slots per phase 
and pole being 3 and the pole are ratio 0.65, the form 
factor k will be equal to 2.26 and from Equation (33) the 
useful flux is equal to | 
500 
10° X L37 2.26 X 25 X 24 X 3F,., where F, = 7.1 X 10°. 
. F . . . 
The ratio B. indicates that the teeth section under a pole 
t 
