ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 157 
2 90. 
292. 
293. 
In Fig. 73 the test data of this generator is given, which 
indicates a cos PY = 0.8 inductive drop of 550 volts and 
a maximum excitation of 5,660 ampere turns per pole. 
Current Density in Field Winding.—The number 
of turns per pole being 80, the maximum excitation 
5,660 
80 
The field winding consists of No. 1 S.W.G. wire, which has 
a sectional area of 0.07069 square inch, so that the 
70-75 
0 O07: 69 
= 1,000 amperes per square inch. This value is a very 
liberal one, as seen from the ealeulation of the tem- 
perature rise in the field coils, see Par. 293. 
Length of Field Winding.—The length of mean field 
turn measured from the drawing, Fig. 71, is 28 inches; 
_ therefore the total length of the winding of the 64 coils 
is equal to 64 <X 80 X 28 = 143,360 inches, which represents 
143.360 8 
0.07069 * lu’ Aue ohms. 
current will be = 70.75 amperes. 
maximum current density in the wire will be 
a hot resistance of 
Excitation Voltage.—For the maximum excitation of 
71 amperes, the terminal pressure on the field winding 
must be 71 X 1.62 = 115 volts; or, taking into account 
the various losses in the brushes and connecting eables, 
an exciter voltage of 125 volts will be found sufficient. 
Temperature Rise in Field Winding.—tThe totai 
weight of field copper is equal to 
143,360 x 0.07069 x 0.32 = 3,250 Ibs., 
and the maximum energy required for same is 
71? x 1.62 = 8,200 watts, ° 
for which there is a radiating surface composed of the 
external cylindrical surface of 
64 X 7.37 X 31 = 14,500 square inches, 
