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Nature of 3-phase TR rectifier

Hi there,

I need a good understanding of the attached rectifier circuit.
Requesting all experts to explain how it works, its function and advantage and disadvantage as well.

Guide me for further development, how could we modify it.

This system contains 3phase, 380V, 50Hz ac input, secondary surge protector, Aux Tr ( single phase, 380V/220V, 300VA), phase transformer( 3ph, 380v/12v,0v,12v,100VA) and a main transformer MTR( 3ph, 380V/9V,18V,800VA),SCR(1600V, 50A) bridge, DC reactor( DC 20V,20A). Rectifier output should be DC 20V 20A.

Assume that the I/O control board

1. PTR secondary windings phase, amplitude and rating controller.
2. MTRs secondary fuse (690V, 32 A) sensing
3. SCRs switching controller.
4. 50mlV, 30A shunt sensing,
5. GPS communication,
6. RSM
7. LAN
8. Display....etc,

9. Automatic MCCB trip.

Kindly recommend me one.
Related research papers, articles and ideas.




Well-Known Member
Most Helpful Member
It's a lot more than a "rectifier"...
It appears to be either a stabilised power supply or power controller / speed controller.

Without knowing what the load on it will be, it's not possible to recommend any particular type.

Also, that level of monitoring or telemetry on such a device is not common; most PSUs have no or little fault indication, drives have somewhat more but still often only some digital status indicators.
It's a lot more than a "rectifier"...
Look it as much easy as possible, this rectifier supply constant voltage and current in variable mode, DC 20V 20A.

Without knowing what the load on it will be, it's not possible to recommend any particular type.
DC voltage and current are measured using suitable load..1% to 100%.

Now take a look the table, which category would you like to choose it?


Well-Known Member
Most Helpful Member
This is a three phase bridge rectifier:

Your block diagram is nearer the three phase version of this, plus the low voltage transformer:

But you want far more monitoring...

A "rectifier" just converts AC to DC. It's not voltage or current control.

One of these should give you the 20V @ 20A from a three phase input:

They are preset for 24V industrial standard, but have a multi-turn potentiometer to adjust the voltage as required.
You can get an add-on "signalling module" to provide more status information.

[Edit - typos].
Last edited:

Les Jones

Well-Known Member
Hi rjenkinsgb,
I think you have missed the fact that the top three diodes in the bridge are SCRs. I also think the circuit is badly drawn as it looks like the bottom half of the bottom two secondaries is shorted out.
Just a part explanation to the TS of the three phase input transformer. The primary is wired for delta connection and the secondary is wired in star connection. Item 19 is a choke output filter. The schematic is not clear enough to see the components in item 26


Les Jones

Well-Known Member
Hi rjenkinsgb,
Sorry for the wrong conclusion. I had jut looked at your link to the picture of the three phase bridge and jumped to the wrong concusion that it was being suggested as a replacement for the SCR controlled bridge. Reading though the thread agin it looks like the original question was an exam question. I would like to know the background to question. If it was just something the OP had been give to repair I do not think he would have created the decision tree diagram. The descripion of the control board also seems odd. For example why would it need GPS ? Also he talks about modifying it but does not say what extra functions he wants to add.



Well-Known Member
Most Helpful Member
Ignoring most of the schematic and only paying attention to the 6 SCRs (or thyristors)...it is a phase controlled rectifier bridge.

It works just like a half-wave or full-wave diode rectifier, except it's three phase. And also that thyristors are being used instead of diodes.

Since thyristors are being used, you don't need to begin conducting immediately at the beginning at the beginning of each AC half-cycle (a diode would start conducting immediately and stay conducting all the way until the end of the AC half cycle when it turns off).

With a thyristor, you can wait until partway through the AC half cycle and then trigger the thyristor to start conducting. This lets you transfer less energy to the output of the rectifier so you can also use it as a regulator.

You cannot choose to turn the thyristor off after you turn it on. It only has an ON signal. No off signal. The thyristor will automatically turn off only when the current through it drops to zero due to some other part of the circuit. In this case, this will happen automatically at the end of every AC half cycle when the current crosses zero.

It's like combining a light bulb dimmer switch with a diode rectifier.


The rest of your question is too vague and/or broad to answer since we don't actually know what it is you are asking about.
Last edited:
Dear Sir Dknguyen, your explanation make sense for sure. Its a non regenarative 3 phase rectifier. I need to put all calculation first. Load current, outout voltage, ripple factor, power factor, utilization factor, SCR firing current, RMS voltage etc. Please share a related document or link.

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