ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 63 
and as a standard armature stamping is often utilized for 
various sizes of alternators the introduction of machines 
with the same bore but different core lengths usually takes 
place. 
110. Example 12. A 300 KVA. three phase generator, run- 
ning at a speed of 430 revs. per minute, has 14 poles, each 
earrying a coil of 130 turns of No. 48. W. G. wire. The 
coils are designed for the maximum number of 7,150 am- 
pere turns with the full current of 55 amps. What is the 
loss in the field winding? 
Solution: The sectional area of the wire being equal to 
0.0423 square inch, the current density will be 1,300 amps. 
Fig. 33.—LENGTH OF MEAN TURN IN FIELD Cort. 
per square inch, which is a liberal figure considering that 
the peripheral speed is 96 feet per second, and the winding 
depth is about 13 inches. 
Fig. 33 gives a sectional view of the pole with the magnet 
coil, from which we obtain the length of mean turn, viz., 
34 inches; consequently the total length of the field wind- 
ing will be 61,900 inches, corresponding to a weight of 840 
lbs. (See Table 12.) 
From Fig. 31 we find an energy loss of 3,400 watts, when 
taking the temperature of the coils as 140 degrees F., the 
temperature on which the curve is based. 
From Table 12 the cold ohmic resistance of the 14 magnet 
coils in series is equal to 1.0 ohm. 
Printed in U.S. A. 
