88 § ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
to be considered and the same may be said about those of 
the path 1, especially if the air gap has moderate values. 
For the sake of simplicity one neglects these items and it 
will be found that the following expression of the field 
leakage reluctance is entirely satisfactory, reference being 
again made to Fig. 42 for the meaning of the symbols: 
he 0.313 ae 
"dex, ad xf xa ae Oe (23) 
n mm . m-+b 
149. Example 1%7.—The values d, f and b are already given in 
Par. 14353 and further c = 1.4 inches; n = 6 inches; and 
m = 7 inches. Substituting these values in Formula 
(23), we obtain as the reluctance value of the field leakage 
path : 
sie 0.313 _% 
» ~4AX1.4X17 , 4X10X17 , 4X6X10 10" 
6 7 Sa: § 
Ans. 
This value is about 3 times larger than the reluctance of the 
air gap. The reason for this comparison will be found in 
Pars. 154 to 158, where the leakage coefficient of the 
whole magneti¢ circuit is discussed. — 
150. Reluctance of Armature Leakage Path.—tThe ecal- 
culation of this item is one of the most difficult tasks of the 
designer, as the conditions are far too complicated to take 
into account all the different factors, such as the class of 
winding, form of the coils, form of the armature magnetic 
field, saturation of the teeth, influence of the idle iron 
parts near to the armature body, ete., 
It is considered satisfactory to calculate the value of the 
reluctance of the armature stray field within 10%. 
Formula (24) will answer the purpose in most cases, 
especially if the reluctance items are considerable. 
