ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 179 
total field ampere turns, corresponding to the normal open 
circuit voltage and the normal armature back ampere 
turns. Consequently the poles have to provide for 52,400 
ampere turns, or each pole has to carry a normal value 
of 6,500 ampere turns. 
342. Field Winding.—In all probability, the depth of the 
field windirg will be very close to the upper limit of 2 
inches; therefore, we will not allow a greater current 
density than 1,000 amperes per square inch. 
Assuming an average space factor of 0.4, including the 
space taken up by the bobbins and end plates, the 
6,° 00 
1,000 x 0.4 
necessary winding space is equal to = 16 square 
inches. 
Fig. 78 shows that with a pole height of 8.5 inches sufficient 
space is obtained for the winding. 
343. Principal Dimensions.—The principal dimensions of 
the machine in question are as follows: 
MePOrOLOTIIATUTC $s) mo... 6 sepa bev dasenckudess 47.5 inches; 
external diameter of armature core.......... eS 
TAREE Oc Friis nodes o's 9k ¥ ircko o fiw 5 Pele Sv nb ors 
EMP iy Siena 5 G.ss i Dipl e ls Fa ek 4 hae « bo aa 
overall length of armature, including two 
TEE DOES. oo kp ca oo os Pee Cake oe he 12 te 
MRO Ee oc sles saiecee wes oa ole ele'ss 11 a MES 
st og dena Ny la Al a ak eee Wirdateta Weck Bre? Seat 
MUMTO WAGE. ols cole ate vss scga'cdecepee’s 8 Sars 
ON 1) a rr re ret ie: RAR Ode Rot ae 
Memee! Pim feneth. oie lw. tk ee ee Be saaceels 16:0. SSS 
PE TT TINCT E oN pie g die ab dou d' cg ucegeseees ON See 
These dimensions are subject to slight alterations, as detailed 
calculation may require, see Fig. 80. 
(344, Air Gap.—For the approximate determination of the air 
gap, we will assume that the no-load characteristic will 
