ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 95 
due to the fact, that the E. M. F. of the armature of an 
alternator is directly proportional to the flux which cuts 
the armature coils, as expressed in the equation: | 
kxnxZx F, 
E aI 10° ] 
where, k is the form factor characterizing the wave form 
of the E. M. F. and is more or less constant for 
any degree of saturation ; 
n, the number of cycles per second; and 
Z, represents the number of armature conductors 
per phase. 
For any particular alternator these values are constant; con- 
sequently the E. M. F. of the armature depends only on the 
number of useful magnetiec-lines F,. 
166. Useful Flux.—Further, it may be stated, that the ampere 
| turns required to generate a useful flux of F’, per pole are 
expressed in the equation: 
A,=r,xF,xO+rx Fi +r, x F,....(34) 
where, A, is the number of ampere turns or the E. M. F. 
of one pole, 
r, represents the magnetic resistances of the vari- 
ous paths; 
F, the useful flux, which we assume is equal to that 
passing through the air gap and armature 
system ; 
F, X 6, the value of the flux originated in the field 
system, from which we may assume that it is 
constant for all parts of the field path; and 
6, the leakage factor which indicates the ratio of 
the field flux to that of the armature. 
167. Proper Determination of No-Load Character- 
istic.—From Formula (34), it follows, that the proper 
determination of the magnetizing or no-load characteristic 
