High power transformer phase control

[max]

Hi,

I need to control a spot welding 200kva single phase transformer using scr
phase control, please advise methods and what precautions are necessary
for zero crossing sensing and scr gate triggering. the voltage is 400vac using
two phases.

Regards

[Sideshow Bob]

You do have ICs that implement that
https://www.google.com/search?q=zero+crossing+triac+driver
However driving a transformer this way may perhaps not be doable. Because due to many reasons. We had a lengthy discussion about how to handling powering on large transformer 50/60 Hz transformers a few years back. Even loosing a few cycles may demagnetize the core

[max]

I have an analog controller which is working ok with 200kva transformer,
I am tracing the sch when it is ready i will post it,
I hope someone can simulate it in proteous to get the waveform.

Regards

[bobcat1]

Hi

Driving a transformer with a Triac (not SCR)  is problematic - due to lenz law creating a huge current spike while switching a high inductance coil

All the best

Bobi

[Sideshow Bob]

If your device sits on the primary side. What I think your device is, is a transformer softstart device to avoid high current at startup. A telltale would be if you have a relay in parallel with the triac. This relay will short out the triac at the point steady for the transformer is achieved 

[bobcat1]

If your device sits on the primary side. What I think your device is, is a transformer softstart device to avoid high current at startup. A telltale would be if you have a relay in parallel with the triac. This relay will short out the triac at the point steady for the transformer is achieved 

This might work if the timing will no longer then 300msec - use a micro to control the relay and the TRIAC

All the best

Bobi

[cicos]

There are devices that work by switching on the primary transformers available on aliexpress, but they have their drawbacks (I have one of those) and now I will try the modification that I found on YT.
Pozzz, JaMi

[max]

in spot welding machine every mains cycle is controlled,
in some low power welding the transformer is on only for one or two
mains cycle, the phase angle is controlled for every half cycle according
to the output current requirement.