142 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
! resistance is to be determined and the graphical solution 
earried out as in Fig. 70. 
246. Actual Drop.—For cos p= 0.8 inductive full load, a 
700 : : 
voltage drop of 3.500 — 20 per cent. is obtained; and for 
: 30 
a non-inductive full load the voltage drop is equal to 3.500 
= 8.6 per cent., which is somewhat larger than the average 
value and has been already predicted in the preliminary 
criticism of the design. 
24%. Calculated Excitation Current.—From Fig. 70 it 
follows that if the armature carries a cos Pp = 0.8 lagging 
current of 66 amperes, the excitation ampere turns must. 
be equal to 8,550, in order to maintain the normal terminal 
E.M.F. of 3,500 volts. 
The number of pole turns being 35, the maximum excitation 
8,550 
35 
current required is equal to = 244.5 amperes. 
248. Excitation at Half Load.—In order to calculate the 
excitation losses on inductive half load, the regulation is 
determined for an armature current of 33 amperes. The 
graphical method gives in this ease a field excitation 
of 7,000 ampere turns, or an equivalent current of 200 
amperes.. 
249. Current Density of Field Winding.—The specific 
utilization of the field copper is very satisfactory, as the 
current density for the maximum excitation is equal to 
244.5 
0125 X 1.145 
corresponds to a loss of 7.5 watts per one pound of 
copper, see Fig. 31. The use of edge wound, bare, flat 
copper strips, would permit a slightly higher current 
= 1,740 amperes per square inch area, which 
