In metal industry application there are a traditionally a lot equipment needing single phase power:
induction heating, induction melting, direct resistance heating, resistance welding, spot welding and electroslag remelting (ESRR seems just to be a new variant of that old process)
The basic reason for requireing single pahse power, is that there is only one load which can't be split to three phases.
When symetric connection of such a load to the supply is intended, there are basicly two solutions:
Classic soltuion: Steinmetz circuit
The power factor of the load is compensated and the load is connected between two phases, one additional inductor and one additional capacitor, both properly sized, connected in the other sides of the delta, ensure symmetrical line currents. However, since load paramters tend to change continously during process, you need a lot of switchgear to addapt all the components properly.
Converter solution: A converter with three-phase input and single phase output is used. Such equipment is availble with up to 16 MW using thyristors and up to 4 MW using IGBT
In both cases you have to keep in mind that the key to provide symmetry is to store energy periodically. Therfore all solutions only using transfomrers fail to provide a sound solution for a single load.
The Scott-Connection is fine when you have two single phase loads with of similar power.
