ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 169 
pole core length, so that the value of air path ampere 
turns may be taken for 
0 X 0.313 
2,800 = ret 
For the particular design in question, the result of the above 
equation will be an air gap © of 0.176 inches. We, there- 
fore, base our detailed calculation on a gap value of 0.15 
inch. 
xX 3.6 X 10° = 6 x 15,700. 
316. Leakage Factor.—For the exact determination of the 
no-load characteristic, we have all the data except the 
leakage factor, which, according to Par. 154, will be 
Tr 8 
Tr it gee = 188; 
since 7,= se wee 
2 12X6X2.29 , 12X6X(0.2+0.4) 10°’ 
3.09 X0.15 3.09 x (0.20.15) 
> Sere 0 313 “35.5 
*4X1X12 ,4X12XK5 | 4X3.75X5 ut" 
| SESS. ae ae 
31%. Characteristic Curves.—In Table 19 the different 
data is collected and four points of the no-load character- 
istic determined. So far the results are satisfactory, be- 
cause the normal voltage comes at the knee and the curve 
part above this point is not too flat; and, further, because 
the value of the normal field ampere turns is close ta 
that which we had in view. For the form of the character- 
istic see Fig. 77. 
318. Short Circuit Characteristic.—To effect the deter- 
mination of the short circuit characteristic the factor ks 
has to be calculated. 
The reluctance 7,’ is equal to 
0.313 _ 47.5 
4X 2.15 12XB.1  4X2.15X2.3X (9.38+3.1) 15 10°” 
0.89.3 9.3X3.1 
