252

ELECT. RICAL APPARATUS

single-phase rectification. In polyphase rectification, the seg-
ments and circuits may be in star connection, or in ring connec-
tion, or independent.

Thus, Fig. 105 shows the arrangement of a star-connected (or
F-connected) three-phase rectifier. The arrangement of Fig. 105
is shown again in Fig. 106, in simpler representation, by showing
the phases of the alternating supply circuit, and their relation
to each other and to the rectifier segments, by heavy black lines
inside of the commutator.

Fig. 107 shows a ring or delta-connected three-phase rectifier.

Fig. 108 a star-connected quarter-phase rectifier and Fig.
109 a quarter-phase rectifier with two independent quadra-

FIG. 112.—Voltage waves of quarter-phase star-connected rectifier.
ture phases, while Fig. 110 shows a ring-connected quarter-phase
rectifier.
The voltage waves of the two coils in Fig. 109 are shown as
ei and 62 in Fig. 112, in thin lines, and the rectified voltage by the
heavy black line, eQj in Fig. 112. As seen, in star connection, the
successive phases alternate in feeding the rectified circuit, but
only one phase is in circuit at a time, except during the time of
,tne overlap of the brushes when passing the gap between suc-
cessive segments. At that time, two successive phases are in
multiple, and the current changes from the phase of decreasing
voltage to that of rising voltage. Only a part of the voltage
wave is thus used. The unused part of the wave, ex, is shown
shaded in Fig. 112.
Fig. 113 shows the voltages of the four phases, eif e*, e3, e4, in
ring connection, Fig. 110, and as eQ the rectified voltage. As
seen, in this case, all the phases are always in circuit, two phases
always in series, except during the overlap of the brushes at the
gap between the segments, when a phase is short-circuited dur-
ing commutation. The rectified voltage is higher than that of
each phase, but twice as many coils are required as sources of
supply voltage, each carrying half the rectified current.