178 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
7.1 X 10° ; = 
must be equal to “95,000. = 75 square inehes, and conse- 
é 5 
quently the armature length will be sh 
0.9 X —— 2.07 x 1.4 
= 10.3 inches, including the paper insulation. After two 
half-inch ventilating ducts are provided, the overall length 
may be taken as 12 inches. oto 
339. Height of Core.—For the determination of the armature 
core height, a magnetic density of 47,000 lines per square 
inch should be taken, see Fig. 26, and accordingly the 
iron above the slots will be fixed as 7.5 inches. 
340. Particulars of Pole Pieces.—When designing the pole 
: pieces, the pole shoe height should be taken as 1.25 inches 
and the length of the’ pole core as 11 inches. 
_ Assuming an average leakage factor 9, of 1.25 and a pole 
core density of 105,000, the pole core section should be 
6 
: - = = 85 square inches and the pole width 11x 0.96 6. 
= 8.0 inches. 
The material of the wheel rim in the present design should 
be east steel, with a section of 3.1 by 18.5 inches, resulting 
in a saturation of — = 77,000 lines per square inch. 
For the determination of the pole core height it is necessary 
in the first instance to procure the approximate value of 
the field ampere turns per pole, and calculate the space 
occupied by them. — 
341. Armature Ampere Conductors.—The number of 
total armature ampere conductors has been fixed as 74,600 
and the value of the back ampere turns is.equal to 2.12 x 
12,430 = 26,200. 
With regard to the specified voltage Secs Mebteh is an average 
figure, the value 2.0 is assumed as the ratio between the 
