138 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
240. Various Iron Sections.—The various iron sections of 
the armature have been already determined in Par. 231 
to 235, and the air path reluctance is given in Par. 238. 
The sectional area of the pole core is equal to f X b X .96 
= 9 X 6 X .96 = 52 square inches; and that of the wheel 
rim, g Xh = 15.5 X 3.25 = 50 square inches. 
241. Respective Path Lengths.—The various lengths of 
the paths are taken from Fig. 66 and systematically col- 
lected in Table 18, together with the various sectional 
areas and magnetic densities. ; 
By means of Fig. 46, the value of the ampere turns per 
unit length of the differently saturated parts may be 
fixed, and by multiplying them with the respective path 
lengths, the value of the necessary ampere turns for the 
iron paths is obtained. 
The amount of ampere turns utilized for the air path is 
equal to the reluctance multiplied by the useful flux. 
242%. The Resultant Open Circuit Characteristic.—The 
open circuit characteristic resulting from the calculation, 
will be found in elose accordance with that obtained by 
tests on the actual machine. | 
It should be noted that the greatest contribution to the iron 
path is located in the field system and that the normal 
open circuit voltage is just on the knee or bend of the 
curve, where the ampere turns belonging to the iron path 
are about 25 per cent. of the total value, as 
1.460 5 
5,580 
243. Calculation of the Factor k,.—The determination of 
the short circuit characteristic is very simple. .In the 
first instance it is necessary to calculate the factor k, of 
Equation (15). 
According to Equation (29) this factor can be expressed 
