ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 171 
In the first case, see Par. 299, a 4 per cent. drop is specified 
and in the present design 4 per cent. is obtained. 
In the second condition, the specified drop is 12 per cent., 
whereas the calculated drop amounts to 12.3 per cent. _ 
From the above it is evident that the most difficult part of 
electrical design is successfully achieved and there is no 
difficulty in obtaining the specified efficiencies and temper- 
ature rise, which are simply average values. 
320. Calculation of Field Winding.—In accordance with 
the data of Fig. 77, the maximum excitation per pole is 
equal to Z X C = 5,340 ampere turns; or, total for all the 
poles, 2p X Z X C= 12 X 5,340 = 64,080 ampere turns. 
The field winding has to be calculated for a pressure of 65 
volts at its terminals, in order to obtain the necessary 
maximum ampere turns. ; 
The above condition can be expressed by the deuationa, 
65 = 64,080 7 x = , and 64,080 = 2p X Z X C, where L 
is the mean length of field turn and q the sectional area of 
a conductor. 
321. Section of Conductors.—Assuming a total winding 
depth of 1.5 inches, a rough sketch indicates a length of 
mean turn L, equal to 36 inches; Beye a ye the condue- 
4.0 0 
: = Xx 36 = 0.0285 square 
tor section is equal to g= 
inch. 
The nearest wire to this section is a No. 6 S.W.G. of 0.02895 
square inch. 
For the maximum excitation, we will allow a current density 
of 1,700 amperes per square inch, so that the corresponding 
eurrent will be 0.02895 xX 1,700 = 49 amperes, and the 
0 
= 110, which may be 
number of turns per pole - 
arranged as indicated in Fig. 76, the number of layers 
being 5 and 6 and the total depth 1.4 inches. ' 
