Page 346 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Three 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 or thyristors

We saw in the previous tutorial that the process of converting an AC input supply into a fixed DC supply is called
Rectification with the most popular circuits used to perform this rectification process is one that is based on solid-
state semiconductor diodes.
In fact, rectification of alternating voltages is one of the most popular applications of diodes, as diodes are
inexpensive, small and robust allowing us to create numerous types of rectifier circuits using either individually
connected diodes or with just a single integrated bridge rectifier module.
Single phase supplies such as those in houses and offices are generally 120 Vrms or 240 Vrms phase-to-neutral,
also called 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 circuits are similar to the previous single-phase
rectifiers, the difference this time is that we are using three, single-phase supplies connected together that have
been produced by one single three-phase generator.

Block diagram of three phase rectifier

Advantage of three phase rectifier

The advantage here is that 3-phase rectification circuits can be used to power many industrial applications such
as motor control or battery charging which require higher power requirements than a single-phase rectifier circuit
is able to supply.
3-phase supplies take this idea one step further by combining 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: 360o χ 3 = 120° as shown.
Waveform of Three-phase

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CITS : E & H - Electronics Mechanic - Lesson 223 - 236