ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 183 
characteristie indicates that the specified condition of 
voltage drop is satisfactorily complied with, though a 
reduction of the air gap to 0.24 inch would make the 
agreement still closer. 
348. Particulars of Field Winding.—From Fig. 81 we 
‘obtain a maximum value of field ampere turns per pole 
equal to 10,200 ampere turns, while the corresponding 
excitation voltage on the slip rings is specified as 120 volts. 
For the maximum excitation we will allow a current density 
in the field winding of 1,400 amperes per square inch. 
Therefore, the number of turns and size of wire may be 
calculated as follows: 
uke XX Seed 8 oe R10 ROOMS. 8 0 086s: 
q 1U qd lu 
The length of mean turn is equal to 47 inches, so that the 
conductor section will be 0.0255 square inches, or with 
the nearest standard wire, No. 7 S.W.G., 0.0243 square 
inch. With this value the current is equal to 0.0243 x. 
, 10,200 
34 
120 
1,400 = 34 amperes and the turns per pole to 
== 300. 
349. Temperature Rise.—The resistance of all the coils in 
series is equal to oar x = = 3.7 ohms, and the 
maximum current is 34 amperes; therefore, the maximum 
energy consumption will be 34* x 3.7 = 4,300 watts. 
The temperature rise will be 60° F., as the cooling surface is 
equal to 5,100 square inches, and the mean value of the 
peripheral speed, 3,500 feet per minute. 
350. Armature Losses.—The armature winding has a length 
of mean turn of 92 inches and a resistance per phase of 
36 X 92 8 
X= = 0.0156 ohm; therefore, with the nor- 
7 X 0.02483" 1U0" 
