In the past, it was solved this way. A heavy contactor powers on stage 1, stage 1 powers another heavy contactor powering stage 2, stage 2 does the same with s

In the past, it was solved this way. A heavy contactor powers on stage 1, stage 1 powers another heavy contactor powering stage 2, stage 2 does the same with stage 3. When mains voltage is too low, the contactor cannot close. This way this allows for tens of milliseconds of separation in between power ons.