286

ELECTRICAL APPARATUS

netic flux produced by the primary coil, through the secondary
coil, in the direction opposite to the direction, in which it would
send the magnetic flax through the secondary coil when in the
position I', shown in dotted lines. In vertical position, the
inductor, I, would pass the magnetic flux through the primary
coil, without passing it through the secondary coil, that is, with-
out inducing voltage in the secondary. Thus by moving the
shuttle or inductor, I, from, position I over the vertical position
to the position I7, the voltage induced in the secondary coil, S:
is varied from maximum boosting over to zero to maximum
lowering.

164. Fig. 146 shows a type of machine, which has been and
still is used to some extent, for alternators as well as for direct-

FIG. 146.—Semi-inductor type of machine.
current commutating machines, and which may be called an
inductor machine, or at least has considerable similarity with the
inductor type. It is shown in Fig. 146 as six-polar machine,
with internal field and external armature, but can easily be bxiilt
with internal armature and external field. The field contains
one field coil,.?, concentric to the shaft. The poles overhang the
field coils, and all poles of one polarity, N, come from the one
side, ail poles of the other polarity from the other side of the field
coil. The magnetic structure thus consists of two parts which
interlock axially, as seen in Fig. 146.
The disadvantage of this type of field construction is the high
flux leakage between the field poles, which tends to impair the
regulation in alternators, and makes commutation more difficult
for direct-current machines, It offers, however, the advantage