A rule of thumb for motors at 400 to 440 volt range at 50 Hz is 2 amps per Kw, this really only applies to under 20 KW, so as the KW output rating goes up, the amps required go down, so when you get to 160 Kw about 10 to 15 % reduction can be applied, mainly because the fan requires a lower % of the energy to do its job and newer motors have a higher efficiency.
So you should be using the top line on the motor label 420 v 50Hz 160 Kw 990 Rpm 273.6 Amps.
The over load of the motor should be taken back to 300 amps which is the lowest setting available on your overload as the motor full load amps is 274 amps.
A 160 Kw motor according to motor / fuse rating charts requires 355 amp fuses for direct on line or in your case 315 amp fuses for an assisted start a curcuit breaker would require similar settings.
I have worked on many auto transformer starters.
The right hand contactor should be the first one to close, followed almost immediately by the middle contactor, then once the motor is very close to full speed, Once the Ammeter shows a low amperage below 250 amps .
At this point and you say 5 seconds the right hand contactor will open, this removes the star point on the auto transformer.
Whilst current will still flows through the windings of the auto transformer for part of a second whilst the right hand contactor drops out, once that has happened the left hand contactor will close this is the main run contactor.
The Right hand contactor dropping out and the left hand contactor coming in will be almost the same time.
I believe you are saying that the motor breaker trips when it is trying to start.
My suggestion is to make sure the right hand contactor has not got any welded contacts.
Also I would shift the timer to say 10 seconds to make sure there is plenty of time for the motor to get up to speed and monitor the ammeter to see how the start reaction goes.
Do they try to start the motor with a load in the hopper