186 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
obtain a sinusoidal wave form, we take an armature core 
with 6 slots per pole, but only 4 of them to contain the 
armature winding, while two are left empty. The slots 
should be open and the coils former wound. 
The winding applied is illustrated in Fig. 82, and the ratio 
between the coil breadth and pole pitch in the present 
ease is one-half. 
For the pole are ratio we choose a value of 0.6, so that the 
form factor will be equal to 2.2, see Table 14. 
358. Diameter of Bore.—For the choice of diameter of bore 
the data in Table 16 gives in this particular case satis- 
factory values. The 520 KVA., 300 revs., 60-cycle single 
Fie. 82.—Winpine DIAGRAM oF 520 KVA., SINGLE PHASE 
ALTERNATOR. 
phase alternator under discussion, corresponds to a 750 
KVA., 50-cyele polyphase generator, which has a bore of 
84 inches. Taking into consideration that the number of 
poles is 24, against 20 of the polyphase machine, an 
armature bore of 87.5 inches will be found very suitable. 
Neglecting the small difference between the armature bore 
and wheel diameter, the peripheral speed is equal to 
87.5 X 3.14 
12 
300 = 6,850 feet per minute. 
309. Armature Conductors.—tThe division of the iron and 
copper sources may be effected by means of Fig. 62, in 
choosing a flux value which corresponds to an output of 
about 30 per cent. higher than that of the single phase 
alternator. 
