Spreading the load of a two-phase spot welder

[ADAC]

We have a 400A (nameplate value) spot welder which connects to two phases of a 415V three phase system. The three phase system is supplied via a 22KV/415V 1000KVA transformer (1400A secondary amps).

When operating there are, not unexpectedly, a lot of voltage fluctuations. However we would like to reduce the level of these fluctuations. One possibility that has been raised is to install an isolation transformer that would spread the load more evenly across the three phase supply.

Is this viable, would it work and if so how would we specify such a transformer?

 

[busbar]

You are likely out of luck in this case. Powering a welder as described cannot be done with an isolation or any other transformer. If someone claims it’s possible, I would leave. A “LeBlanc” transformer connection is rumored to do this, but does not work for this purpose. The type of welder that you want rectifies three-phase AC to 2-pole DC [with possible stored energy in the form of capacitors that can be charged at a lower rate than discharged.] The intent is to limit voltage flicker and voltage unbalance. This is the only means by which it can be done for balanced 3ø loading/operation. Four-hundred-volt 2-wire service is not “two-phase”—it is still considered single-phase.

The alternatives are a new unit, or a very pricey redesign. A search for “three-phase DC spot welder” will give an idea of availability.