Firstly, a 5.5kw motor on 3ph 400v will draw approx 11 amps FLC so the overload, at 5 amps is undersized. Ensure your overload can be set to 11 amps.
The motor, according to the nameplate, should only be connected in either star Y
or delta
If it's a dual voltage motor then it'll be 400v Y, if a bog-standard 3ph motor more likely delta but confirm that with motor plate. If you connect it incorrectly you'll soon smoke the motor.
I'm sure you do understand that the connection has no real-life function as a speed control. If that motor is a 1500rpm motor then changing from star to delta will not change the speed for use.
Of course, you can use star-delta as a starting method only, not a speed control. The 'slow' speed in star-delta is the reduced torque building up to overcome the inertia of the load.
To reiterate the two-speed motor possibility (albeit unlikely) this utilises the star and delta connections to alter the usage and connections of the windings... but lets forget this option now.
Finally as one of the posters mentioned... bell the motor windings out then ensure you are getting full voltage through the DOL to the motor. Good luck. Please let us know what you find.
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