94. 
ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS, 
162. 
163. 
164. 
165. 
Calculation of Open Circuit Characteristic. 
Example 20.—In a two phase generator, which has 64 
slots each containing 12 conductors, the number of turns 
1; ; 
per phase will be oS = 192; and if the armature 
current is equal to 400 amperes, the value of the back am- 
pere turns will be 
A, = 141 x 400 x 192 = 108,290. Ans. 
Example 21.—If a three phase generator has 924 con- 
ductors on its armature, the total number of turns will be 
2g4 — 462, and the number of turns per phase $2 = 154. 
Assuming a current of 90 amperes in each phase, the total 
number of armature ampere turns will be 
A, = 2.12 x 90 x 154 = 29,260. Ans. 
Effect of Armature Ampere Turns on Inductive 
Load.—In the ease of an alternator with an inductive 
load cos » = 0, the armature ampere turns counteract the ~ 
effect of the field ampere turns, assuming that the mag- 
netic leakage is nil. 
It may be stated, however, that a feaktionel part of the total 
armature ampere turns does not affect the field at all, but. 
simply provides the usual armature leakage lines of flux. 
The 
calculation of the no-load characteristic of alternating 
current generators is exactly the same as that of contin- 
uous current dynamos. It is necessary to determine the 
number of ampere turns which are required to drive a cer- 
tain number of lines of flux through the magnetic circuit 
of the machine, and if this is carried out for different 
values of flux, and the latter plotted in terms of their cor- 
responding ampere turns, it will give the magnetizing 
curve of the magnetic circuit, which is, at the same time, 
the open circuit or E. M. F. characteristic. This result is. 
