280

ELECTRICAL APPARATUS

A modification of this type of inductor machine is the Alex-
anderson inductor alternator, shown in Fig. 138, which is being
built for frequencies up to 200,000 cycles per second and over,
for use in wireless telegraphy and telephony.

The inductor disc, I, contains many hundred inductor teeth,
and revolves at many thousands of revolutions between the
two armatures, A, as shown in the enlarged section, S. It is
surrounded by the field coil, F, and outside thereof the magnetic
return, B. The armature winding is a single-turn wave winding
threaded through the armature faces, as shown in section S and
face view, Q. It is obvious that in the armature special iron
of extreme thinness of lamination has to be used, and the rotat-
ing inductor, I, built to stand the enormous centrifugal stresses
of the great peripheral speed. We must realize that even with

an armature pitch of less than ^o m*
per pole, we get at 100,000 cycles per
second peripheral speeds approaching
bullet velocities, over 1000 miles per
hour. For the lower frequencies of
long distance radio communication,
20,000 to 30,000 cycles, such ma-
chines have been built for large
powers.

160. Fig. 139 shows the Eicke-
meyer type of inductor alternator.
In this, the field coil F is not con-
centric to the shaft, and the inductor
teeth not all of the same polarity, but
the field coil, as seen in Fig. 139, sur-
rounds the inductor, 7, longitudinally,

and with the magnetic return B thus gives a bipolar magnetic
field. Half the inductor teeth, the one side of the inductor, thus
are of the. one, the other half of the other polarity, and the
armature coils, A, are located in the (laminated) pole faces of the
bipolar magnetic structure. Obviously, in larger machines, a
multipolar structure could .be used instead of the bipolar of Fig.
139. This type has the advantage of a simpler magnetic struc-
ture, and the further advantage, that all the magnetic flux
passes at right angles to the shaft, just as in the revolving field
or revolving armature alternator. Ii> the types, Figs. 136 and
137, magnetic flux passes, and the field exciting coil magnetizes

FIG. 139.—Eickemeyer in-
ductor alternator.