150 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
The weight of the cast iron rim together with the arms is 
about 12.5 tons, and the diameter 11.75 feet, so that the 
flywheel effect in this particular part is equal to 12.5 x 
11.75? = 1,730 tons feet square; from which a total effect 
of 2,320 tons feet square is obtained. 
272. Peripheral Speed.—The peripheral speed at the ex- 
ternal diameter of the magnet wheel is 
‘169 X 3.14 X 93.75 
2 1D = 4,150 feet per minute, 
which is much lower than that of a standard speed alter- 
nator of the same capacity. 
In the present case, an increase of the diameter would be 
disadvantageous from an electrical point of view, as well 
as with regard to the economy of material and to the 
mechanical construction and strength of the machine. 
273. Winding Space.—tThe following calculation indicates 
that there is ample room for the necessary field winding. 
The periphery on the bottom of the coils is equal to 
153 X 3.14 = 480.4 inches; so the available space for one 
480.4 3.95 
a: ee 
eoil depth is 1.5 inches. 
eoil side is = 1.78 inches, and the total 
274. Number of Poles.—The number of poles is equal to 
93.75 X p ; 
60 
The value of the pole pitch is 
Dx a __ 169 x 3.14 
= 50 where 2p = 64. 
= 8.29 inches. 
64 64 
| 45+ 5.6 
Fig. 60 gives a pole are of ae = 5.05 inches, so that 
é 5.0 
the pole arc ratio will be er = 0.61. 
8,29 
