Slightly outdated MEDAR industrial spot welding rig

[applicanon]

Found a rather industrial scale spot welding unit in the scap pile and thought I may make use of the components.

unfortunately I made the mistake of tearing down the most of it without much documentation to back it up.

now that I've gotten a handle of what sorts of power electronics I've got and how the work,  I'd like to put the unit 'somewhat' back together as to utilize it for my own project.

The machine came equiped with a beefy SCR based 3 Phase full bridge rectifier, followed by a substantially energetic DC link, and finally rounded up with an IGBT based H-Bridge for the power punch.

I've got full intention on salvaging the gate drive circuitry components for the IGBT's as they were engineered along with a substantial snubber protection circuitry equiped, and it only makes sense to reuse what's already been dialed in for me.

The project end goal would be either an induction heater or a tesla coil, or possibly the ability to remove the IGBT drive unit as a modular system which could be swapped from one project to the other as needed.

Now that I've got all that out of the way.....  On with the stumbling blocks!

The original system was based on PLC technology which controlled both the SCR 3 PH rectifier which would chop it up accordingly to provide the desired DC output voltage, followed by a DC capacitor bus for smoothing, and then a large IGBT h-bridge section for producing medium frequency dc pulses for the spot welding.

Here's a question I have...

There are two current transducers for measuring the output of the IGBT H bridge.  One on each output leg.  There are also something like 6 turns of wire which loop through each of the current transducers as well.  Upon disassembling this system, I took off those extra turns and can't for the life of me remember where they were connected and / or what their purpose was in the circuit.

I have a half ass guess that it may be to do with sensing a shoot through situation, the current transducer tripping a fault, saving the high power IGBT's, but even if this were the case, I'm not sure how it was implement them.

Anyone else have any insight as to what the additional windings may do?

Any input much appreciated!

Pictures of system now (without the extra windings, and further pictures of how system was originally built with the extra windings thru transducers)

[ow19m]

Hello Sir ,
Any Update on the welding inverter you designed yourself ? what was the response for the calculated snubbers used by Medar ? What is the power rating you were using to weld ? Thanks