180 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
take a form such, that for the normal or otherwise mini- 
mum excitation, 70 per cent. of the total ampere turns 
shall be consumed in the air gap. 
In the present case the gap ampere turns will be equal to 
6,500 x 0.7 = 4,550. 
The useful fiux being 7.1 <x 10°, and the air section about 
12 x 11132 square inches, we find that in the first 
approximation, by means of the equation, 6,550 = 
6 xX 0.31 
ae : x 7.1 X 10° the air gap must have a value close 
Te 
s | ° 
+444 3 
; 
: 74\" 
% 
EN 
6 esl" 
yy IE 
nN 
¥ oO 
eae 
Fie. 80.—300 KVA., 375 ReEvs., 25-CrcLk, 3-PHASE ALTERNATOR. 
to 0.27 inch. For further calculations it will be taken 
as 0.25 inch. 
345. Open Circuit Characteristic.—In determining the 
open circuit characteristic, the leakage factor © is equal 
to 1.25, because 
i: 0.313 _t4 
AR 182 x11 12 yc L1(0.22-+0.38) 10% 
2.07°° 0.25 °2.07°° 0.22+0.25 
r 
and 
ie 0.313 _ 35 
"4X 1.25X11 , 4X8.5X11 , 4X8.5X8 10" 
6.5 SE aii 
