Problem in Stardelta Starting

It's an unfortunately common problem with star-delta starting, one they never tell you about until after you have it. There is a phase shift when changing from star to delta and sometimes that happens when the field in the motor has not fully collapsed, essentially creating a situation similar to connecting two generators out of phase with each other. there is a massive voltage and consequent current spike, theoretically in excess of 2000% of the motor FLA, well above the instantaneous trips of the circuit breaker.

The best way to avoid it is to never use star-delta starting, that's my preference. but since you already have it you can try one other thing. You can either rebuild your starter to be a "Closed Transition" version, which is expensive, or you can try a cheaper fix. It's called "rolling" the conductors to try to shift that phase sequence to where you have a leading phase relationship instead of a lagging one.

Take ALL THREE of the conductors on the Delta contactor and move them over one pole; A to B, B to C, C to A. It doesn't change the rotation but it changes the phase shift relationship. Sometimes it works, sometimes it doesn't, you might get lucky.

Personally I would junk it and install a solid state soft starter, they are MUCH better.

There is a link to a paper that describes the problem.