3-phase transformer intermittently shorts (or saturates) and intermittently hums loudly and intermittently stops giving output voltage

Thread Starter

Shamoooot

Joined Apr 3, 2023
27
Hello

I have this problem as mentioned in the subject, which happens when I connect the transformer to a " 3-phase full wave controlled bridge rectifier ".

I have a fully controlled bridge rectifier board of (TYN812RG) thyristors, and I want to trigger it through some firing board which I am sure it's functioning properly.

I am using 400V to 90V/45V center-tapped transformer, which capable of 1.5A supposedly.
There is no protection other than a fuse on the primary windings, and a 3-pole magneto-thermal switch.
Two identical transformers were tested with different rectifier boards and the same is happening..
Here’s the schematic (i don’t have snubber circuits on thyristors):

471gf.png

I have tried several Y and D combinations of the secondary windings.

I tested with these loads:

https://qph.cf2.quoracdn.net/main-qimg-e6d3f8806e169aa1aaea76136d0edac8

I am connecting the thyristors together in the bridge with a real tiny gauge solid core wires.


The signal I am getting out of the bridge but with longer dead zone.

https://qph.cf2.quoracdn.net/main-qimg-49c4475c6616c5dbc550473aac4c17e1

Firing board datasheet:
https://www.docdroid.net/uMz93Hj/document
 

Thread Starter

Shamoooot

Joined Apr 3, 2023
27
there was a problem in the pcb design, the designer mistakenly flipped the cathode with the anode so instead of (K-A-G) as it should be, it was on board (A-K-G) so I ended up lying each thyristor on the heatsink horizontally and then connecting the pins through these wires to the appropriate holes...
 

strantor

Joined Oct 3, 2010
6,837
Ok, so:
Two identical transformers were tested with different rectifier boards and the same is happening..
And
I have tried several Y and D combinations of the secondary windings.
And
(i don’t have snubber circuits on thyristors):
And
I am connecting the thyristors together in the bridge with a real tiny gauge solid core wires.
And
there was a problem in the pcb design, the designer mistakenly flipped the cathode with the anode so instead of (K-A-G) as it should be, it was on board (A-K-G) so I ended up lying each thyristor on the heatsink horizontally and then connecting the pins through these wires to the appropriate holes...
Yet
firing board which I am sure it's functioning properly.
I think you are barking up the wrong tree. You can't just tie all the SCRs together. They need Isolated drive circuitry.
 

strantor

Joined Oct 3, 2010
6,837
Ah, right. Ok you need to use tightly twisted wire, all the same length, to the gates to prevent misfire.the document says no longer than 40cm but I would try to make it even shorter. As short as possible. And you really should be using snubbers. Also this statement still leaves me with questions:
I am connecting the thyristors together in the bridge with a real tiny gauge solid core wires.
Do you really mean connecting them together? As in, joining them? Making them electrically common? These need to be isolated from each other, not joined together.
 

Thread Starter

Shamoooot

Joined Apr 3, 2023
27
I will try the snubber circuit , hopefully it will fix the issue..
Regarding the other question, what I meant was that I connected them according to the schematic with each of them being isolated.
 
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