114 
ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
qualities may be obtained by different designs, such as a 
design having more iron and less copper winding, or one 
resulting in an ample application of armature and field 
copper, but of reduced iron material. 
183. The Use of a Large Number of Armature Am- 
pere Turns.—Take for instance a particular case where 
an inductive cos P —0 voltage drop of 25% is specified, 
which, as already known, involves a certain ratio between 
the numbers of the armature and field ampere turns. 
A large number of armature ampere turns may be chosen, 
resulting in a considerable amount of field winding. The 
fundamental Equation (33) indicates clearly, that in 
this particular case the number of magnetic lines F,, 
passing through the iron body, will proportionally 
decrease, resulting in a decrease of me volume and section 
of the iron. 
184. The Use of a Small Number of Armature Am- 
185. The Influence of the Length of Mean Turn. 
186. 
pere Turns.—If an armature winding with a small 
number of turns is taken, then the turns on’ the field are 
accordingly smaller, but the amount of iron must be large ~ 
in order to carry the necessary flux, which increases as 
the turns of the armature winding decrease. 
In 
conclusion, it should be pointed out that the reduction of 
one material does not effect a proportional increase of the © 
other. For instance in a certain design where the arma- 
ture turns are reduced to one-half the value, the copper 
in this design will not fall to one-half the amount, because 
with the increasing dimensions of the iron, the mean 
length of a turn is also increased. 
Minimum Material Costs.—For certain specified con- 
ditions a satisfactory division of the copper: and iron 
sources will always be found, so that the resulting copper 
