164 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
the iron length with regard to the magnetic density in the 
teeth, which is on the average to be 75,000 lines, see Fig. 
27, in order that the losses therein shall not be excessive. 
ison Equation (38), we obtain for the fixed value of £8 ape 
conductors, a flux per pole of . 
127X10° = 2.46X40x36XF, where F, = 3. 6x10° lines, 
so that the effective teeth section under a pole has to be 
3.6 X 10° : 
about 75,000. 48 square inches. 
307. Length of Armature.—tThe expression of the sectional 
area of the teeth per pole is: - XrxXl=q, where r is 
the mean thickness of a tooth. In the present case the 
pole are a, is fixed as 6 inches; the slot pitch 0, is equal 
to 3.09 inches; the bottom thickness. of the tooth is 
9.26 
aoe: .8 = 2.29 inches, while at the top it is 2.7 inches, 
which results in the mean value of 2.5 inches. Conse- 
48 x 3 09 
6 X 2.5 
quently the effective iron length J is equal to 
= 9.85 inches. = Roe 
Now, taking an additional length of 15 per cent. on account 
of the paper insulation between the laminations and as- 
suming two 14-inch ventilating ducts, the overall length 
of the armature will be 9.85 + 1.45 + 1= 12.3 inches. 
308. Magnetic Density in Armature Core.—The 
standard length of the frame provides for 13 inches; 
therefore, we may take the armature overall length as 13 
inches, having in view a pole core length of 12 inches, in’ 
order to make allowance for the useful leakage. 
According to Fig. 26, the magnetic density in the armature 
eore should be about 40,000 lines per square inch. The 
standard stamping offers, with the fixed length, an effective 
section of 5 X 12 x 0.85 = 51 square inches, so that the 
