102 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
In practice it is found that it is best to keep the pole are 
ratio at about 3 for alternate poles and at about 1 for 
equipole machines. 
178. Example 23.—A 375 KVA. revolving field type, slow 
speed, two phase alternator, with 64 poles, is dimensioned 
as indicated in Figs. 59 and 60. The normal phase voltage 
is 3,000, at a frequency of 50. The armature contains 256 
slots each having 15 conductors. 
M9 
"28" G4" 
' 
te 
' 
Lt 
z | 
| 
» 
— 56 * 
769" 
Pd is 
a” 
" 
‘ 
Fig. 59.—375 KVA., 3,000 Vout, 98% RrEvs., 50-CycLE, 2-PHASE 
ALTERNATOR, 
No-Loap CHARACTERISTIC: In order to determine the no-load 
characteristic, the necessary ampere turns should be eal- 
culated for four different degrees of saturation corre- 
sponding to 3,500, 3,000, 2,500 and 2,000 volts terminal 
pressure. 
Form Facror: By means of Formula (33), the different 
values of the useful flux are obtained, but first of all, the 
value of the form factor must be ascertained. 
