ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 201 
ampere turns of the magnet coil. The choice of this ratio 
factor allows the armature leakage in this design to be 
somewhat higher than in the revolving coil type of alter- 
_nator, and, besides, the value of the short circuit constant 
will also be higher. 
The normal value of the armature back ampere turns is 
0.9 x 16 x 44 x 24 = 15,200 total, or, per closed magnetic 
15,200 
4 
3,800 = 10,500. 
If 75 per cent. of the field ampere turns are allowed for the 
air gaps, the latter will be found from the equation 
0.313 26 
0.75 X 10,500=— 
circuit, = 3,800; and that of the field = 2.75 x 
2.9X10°, where 6=0.22., 
——_—— — +, 
‘Pesan 
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2 yy, 
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Fie. 89.—DIMENSIONS OF MAGNETIC CiRcUIT OF 55 KVA., 
1,050 R.P.M., 70-CycLk, SINGLE PHASE ALTERNATOR. 
For further calculations we take the single air gap equal 
to 0.2 inches. 
$92. The Open Circuit Characteristic.—The data for the 
determination of the open circuit characteristic is tabulated 
in Table 22. A leakage factor © of 1.1 has been applied 
in the caleulations, see Par. 388. 
The air gap reluctance is equal to 
Re 2x0 313 _ 29.5 
°9X2X6 , 6XY9X(0.2+0.5) 10°’ 
3x0.2 " 3(0.2+0.2) 
r 
