1380 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
space available for the winding is equal to 
ae — 2.23 inches, 
which is ample for the coil of 1.125 inches in depth . 
together with an insulating spool, A, 0.06 inch thick and 
the protecting metal spool, M, 0.08 inch thick which is 
placed between the pole core and insulating spool, as indi- 
eated in Fig. 68. 
In a radial direction, the magnet coil has a good tight fit, 
as the following calculation shows: 
The total height of the pole is 7.25 inches. The thickness 
of the pole shoe being 1.2 inches there is left a free length 
of 6.05 inches, which is taken up by 35 0.125-inch copper 
strips, by 37 0.02-inch press-spahn sheets and by two 
metallic projecting pieces, C, as indicated in Fig. 68. 
216. Size Factor.—It will be instructive to check the leading 
dimensions of the alternator, by applying the rule given 
in Par. 196: 
The normal output of the machine is 400 KVA. when 
running at a speed of 500 r.p.m.; the bore of the arma- 
ture is equal to 55 inches, and the iron length with its 
paper insulation 9.5 inches; so that the size factor of the 
alternator will be: 
55’ xX 9.5 X 500 
f = 400 a 36 2k 1s, 
This, when compared with the average value given in Fig. 
64, indicates that the design and leading dimensions have 
not been cut too fine. 
This comparison serves simply as a guide and in no way 
decides if the design is economical, or not. 
21%. Distribution of Material.—In order to ascertain ‘if 
the design will give the reasonable features of a com- 
mercial alternator, together with the most favcrable dis- 
tribution of the material, it is necessary, in the first in- 
— 
