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3-PHASE RECTIFICATION
3-phase rectification is the process of converting a
balanced 3-phase power supply into a fixed DC supply
using solid-state diodes. The rotating rectifier is a full-wave
bridge rectifier and utilizes six diodes (Figure 45) to convert
one full wave of alternating current into one full pulse of
direct current.
U
3-PHASE, 3 WIRE
V
AC SUPPLY
W
Figure 45. 3Ø Rectification
A diode is a semiconductor device that essentially acts
as a one-way switch for current. It allows current to flow
easily in one direction (Figure 46A), but restricts current
from flowing in the opposite direction (Figure 46B).
FORWARD BIAS
A
ANODE (+)
POLARITY (+)
CURRENT FLOW (YES)
ANODE (+)
ACTUAL DIODE
REVERSE BIAS
NEGATIVE
ANODE (+)
LEAD
Figure 46. Forward/Reverse Bias Diode
CURRENT FLOW (NO)
PAGE 44 — GENERATOR SERVICE AND TROUBLESHOOTING MANUAL — REV. #0 (08/29/23)
D
D
D
1
3
5
V
DC
D
D
D
2
4
6
NEGATIVE
LEAD
CATHODE (-)
STRIPE
INDICATES
CATHODE (-)
B
POLARITY (+)
CATHODE (-)
ROTATING RECTIFIER TEST
Single-phase generators are generally 120
square voltage) or 240
line-to-neutral (L-N), and nominally of a fixed voltage and
frequency producing an alternating voltage or current in the
form of a sinusoidal waveform being given the abbreviation
of "AC".
Three-phase rectification, also known as poly-phase
rectification, is similar to single-phase rectification. The
main difference is that three single-phase circuits are
connected together to produced a three-phase output.
I
DC
The advantage is that 3-phase rectification circuits can
+
R
be used to power many data centers, commercial and
LOAD
-
industrial applications such as motor control or battery
charging systems which require higher power requirements
than a single-phase rectifier circuit is able to supply.
3-phase generators combine together three AC voltages
of identical frequency and amplitude, with each AC voltage
being called a "phase". These three phases are 120
electrical degrees out-of-phase from each other producing
a phase sequence, or phase rotation of: 360 ÷ 3 = 120 as
shown in Figure 47.
Three-phase alternating current (AC) can be used to
provide electrical power directly to balanced loads and
rectifiers. Since a 3-phase AC supply has a fixed voltage
and frequency, it can be used by a rectification circuit to
produce a fixed DC voltage.
A
+V
0
90°
0°
120°
240°
-V
Figure 47. 3-Phase Waveform
phase-to-neutral, also called
VRMS
PHASE
B
C
180°
360°
270°
120°
120°
(root mean
VRMS
TIME
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