ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 167 
sufficient exactness the total area of one side of a coil may 
4,000 
1,300 X 0.4 
inches. Now, if we limit the winding depth to say 1.5 
be taken equal to the value: = 7.7 square 
7.7 
inches, then the height of the coil will be is 5 inches, 
see Fig. 76, from which it will be seen that the available 
winding space is sufficient. 
314, Preliminary Dimensions.—Having ascertained that 
the choice of the iron and copper sources and that of the 
leading dimensions, Fig. 74, will permit the execution of 
a successful design, it is necessary to base the ecalcu- 
lations on the preliminary dimensions as follows: 
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external diameter of the armature. ........ ro Aaa eae 
ND ore yc dasa esas 8 ea haces s Wet) s 
SE GD se een ere > ce > ii aa 
overall length of the armature with two 
EMUIPTEIRETOOEN,. Cone csc da eed se mae ee 13 pT a 
EL COEDS Sayer ger airy Sree ger eae 6 tte F 
MNOS UTIL 5 a 5 aca fie anc s «ev see oe vla'e o's ae 
ie SRS S Se TUES Rep ery Senne en 12 vin teen pe 
SUMO MOIONE eke eb ee ete ee 6 : 
The cast iron rim should have a section such that it should 
have a saturation degree which will essentially contribute 
to the number of field ampere turns. 
In accordance with Fig. 74, this section is dimensioned to 
have an area of 3 X 18= 54 square inches, which will 
produce a density of about 43,500 lines per square inch. 
315. Air Gap.—The correct choice of the air gap in the first 
instance will greatly shorten the calculations, and the best 
method of fixing the same will be to determine the normal 
ampere turns of the field, as indicated in Par. 312. As- 
sume that about 70% of the ampere turns are utilized for 
