star to delta conversion formula
Yes, that was also my original understanding of your question. I think, the circuit can be made from a usual wye-delta motor starter (three contactors and a time-relay to define a switch-over deadtime) and a adjustable current measurement relay. The output of the current measement relay should have a sufficient filtering to ignore current transients during switch-over, otherwise additional time-relais for programmable delay can be used.
P.S.: My assumption is, that current consumption will be lower in wye circuit, so a natural hyteresis is created. If this is not the case, the current measurement relay must either have a sufficient hysteresis or two threshold output contacts.