256

ELECTRICAL APPARATUS

and moderate resistance, r, shunted between the rectifier seg-
ments. Fig. 121 then shows the wave shape of the current, i0 — i,
which passes'through these counter e.m.fs., e! (assuming that the
circuit of e'7 r, contains no appreciable self-inductance).

Such polyphase counter e.m.fs. for shunting the differential
current between the segments, can be derived from the syn-
chronous motor which drives the rectifying commutator. By
winding the synchronous-motor armature ring connected and

FIG. 121.—Wave shape of differential current.

of the same number of phases as the rectifying commutator, and
using a revolving-armature synchronous motor, the synchronous-
motor armature coils can be connected to the rectifier segments,
and byepass the differential current. To carry this current, the
armature conductor of the synchronous motor has to be increased
in size, but as the differential current is small, this is relatively

FIG. 122. — Leblanc's Panchahuteur.

little. Hereby the output which can be derived from a poly-
phase rectifier can be very largely increased, the more, the larger
the number of phases. This is Leblanc's Panchahuteur, shown
diagrammatically in Fig. 122 for six phases.
Such polyphase rectifier with non-inductive counter e.m.f.
byepath through the synchronous-motor armature requires as
many collector rings as rectifier segments. It can rectify large
currents, but is limited in the voltage per phase, that is,
per segment, to 20 to 30 volts at best, and the larger the