126 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
In favor of large air gaps, it may be mentioned, that the 
effect of any magnetic dissymmetry is diminished and 
that the eddy current losses are considerably reduced, 
which is of importance where solid pole shoes are used. 
209. Final Determinations.—In summarizing the contents 
of Pars. 181 to 208, it may be mentioned, that for the 
basis of a successful design, the data of Fig. 62 should 
be used, from which the most favorable utilization of the 
iron and copper may be attained. 
The choice of dimensions, the current and magnetic densities. 
and the necéssary mechanical details are then proceeded 
with in such a manner that the specified efficiencies and 
temperature rise are complied with. 
With the object of illustrating the method of calculation and 
to show the adaptability of the empirical data already 
given, the design of actual machines is given hereafter, 
from which the design of various types of alternators 
should be a simple and well understood matter. 
THREE PHASE, REVOLVING, FIELD ALTERNATOR 
DESIGN, 
210. General Specification for Three Phase Alter- 
nator.—A 400 KVA. revolving field type, three phase 
generator, capable of delivering a current of 66 amperes 
at a normal working E.M.F. of 3,500 volts, has the dimen- 
sions indicated in Fig. 66. The alternator, at a speed of 
500 revolutions per minute, generates current at 50 cycles 
per second. The armature is star connected and the wind- 
ing is placed in 72 slots, each slot containing 18 con- 
ductors, which consist of 2 parallel connected No. 9 S.W.G 
wires. The armature coils are former wound and held in 
the siots by means of 0.2 inch thick fibre wedges. The 
coils are properly insulated from the iron by 0.08 inch 
