Soft start... for a transformer
Here's the problem - excessive inrush current is when the transformer is activated close to the AC cycle passing thru zero. Consider the steady-state case: -



Current lags at about 90 degrees and if you applied the supply voltage close to when the voltage peaks, current will naturally not have the problematic inrush state: -



When powering the transformer with a supply voltage passing thru zero a much larger flux density occurs and this saturates the core causing (sometimes) a massive over-current.

If you can find a motor protection device that explicitly states it performs the above function then it should be OK.