Page 182 - Electrical Equipment Handbook _ Troubleshooting and Maintenance

POWER ELECTRONICS, RECTIFIERS, AND PULSE-WIDTH MODULATION INVERTERS

POWER ELECTRONICS, RECTIFIERS, AND INVERTERS 9.9

FIGURE 9.12 (a) A half-wave rectifier circuit. (b) The output
voltage of the rectifier circuit.

is smoother than that of the previous rectifier, but it still contains ac frequency components
at 120 Hz and its harmonics (r 48.2 percent).
Figure 9.13b illustrates another possible full-wave rectifier circuit. Diode D conducts
1
on the positive half-cycle with the current returning through the center tap of the trans-
former, and D conducts on the negative half-cycle with the current returning through the
2
center tap of the transformer. The output is shown in Fig. 9.13c.

The Three-Phase Half-Wave Rectifier
Figure 9.14 illustrates a three-phase half-wave rectifier and its output voltage. At any
instant, the diode with the largest voltage applied to it will conduct, and the other two
diodes will be reversed-biased. The output voltage at any time is the highest of the three
input voltages. The output voltage is smoother than that of the full-wave bridge rectifier cir-
cuit. It has voltage components at 180 Hz and its harmonic components (r 18.3 percent).

The Three-Phase Full-Wave Rectifier
Figure 9.15 illustrates a three-phase full-wave rectifier. The first part of the circuit connects
the highest of the three-phase voltages at any instant to the load. The second part consists of
three diodes oriented with their cathodes connected to the supply voltages and anodes con-
nected to the load. This arrangement connects the lowest of the three voltages to the load at
any given time.
The three-phase full-wave rectifier connects the highest of the three voltages to one end
of the load and the lowest voltage to the other end (Fig. 9.16). The three-phase full-wave
rectifier provides smoother output than a three-phase half-wave rectifier (r 4.2 percent).

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