SCR
Silicon-controlled rectifier
An SCR is a thyristor with a gate-controlled triggering function in its documented circuit.
Schematic
Symbols · SCR REC
Thyristor phase-controlled rectifier
An AC-to-DC converter using thyristors fired at a controlled angle to set its DC output voltage.
In plain English
What does Thyristor phase-controlled rectifier mean?
A phase-controlled rectifier uses thyristors instead of diodes, so the firing angle sets the average DC output voltage. Six-pulse bridges are widely used for large battery chargers, electrolysers, DC drives and older UPS rectifiers because they are robust and simple to control.
A simple example
On single-line diagrams it appears as the rectifier box with AC and DC marks plus a thyristor or control additional drawing mark, or as a bridge of thyristor symbols on detailed schematics. A rectifier transformer, line reactor and harmonic filter are often drawn upstream.
What the drawings help you do
Reducing the output voltage by delaying firing also lowers the input power factor, and the converter draws characteristic harmonics at 5th, 7th, 11th and 13th orders. The symbol does not show these effects, which must be assessed with the network harmonic study.
This particular reference
An AC-to-DC converter using thyristors fired at a controlled angle to set its DC output voltage. A phase-controlled rectifier sets voltage by firing angle; an active front-end rectifier uses switched transistors and can run near unity power factor.
- DC
- Direct current: electricity flowing in one direction.
- AC
- Alternating current: electricity whose direction changes periodically.
- Winding
- A coil of conductor inside an electrical machine or transformer.
Read the source: AutoCAD Electrical: Semiconductor components · IEC graphical symbols for diagrams
SLD / Schematic · SCR REC
What it represents
A phase-controlled rectifier uses thyristors instead of diodes, so the firing angle sets the average DC output voltage. Six-pulse bridges are widely used for large battery chargers, electrolysers, DC drives and older UPS rectifiers because they are robust and simple to control.
On single-line diagrams it appears as the rectifier box with AC and DC marks plus a thyristor or control qualifier, or as a bridge of thyristor symbols on detailed schematics. A rectifier transformer, line reactor and harmonic filter are often drawn upstream.
Reducing the output voltage by delaying firing also lowers the input power factor, and the converter draws characteristic harmonics at 5th, 7th, 11th and 13th orders. The symbol does not show these effects, which must be assessed with the network harmonic study.
How to read it
- A thyristor mark inside or beside the rectifier block distinguishes it from a diode rectifier.
- Expect harmonic filtering or a phase-shifting transformer on large units.
Information to show or reference
- State pulse number and DC rating.
- Show rectifier transformer and line reactor.
- Reference harmonic study and filter design.
A distinction that matters
A phase-controlled rectifier sets voltage by firing angle; an active front-end rectifier uses switched transistors and can run near unity power factor.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
AutoCAD Electrical: Semiconductor components
Public semiconductor symbol family including thyristor forms.
IEC graphical symbols for diagrams
IEC graphical symbol context for converters.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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Schematic
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Twelve-pulse rectifier
Two six-pulse bridges fed from star and delta transformer windings 30 degrees apart, cancelling the lowest harmonics.
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AFE
Active front-end rectifier
An actively switched AC/DC stage using a documented current-control and DC-link regulation arrangement.
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