Thermal Over Load Relay Setting

You can set in TV channel VHF-1. It is curve current and angle current.

In DOL, there is only one value of the current through the relay, it is line current.

In ΥΔ, you can wire it such that the relay is within the Δ. In such a case,as shown below, you need to set the relay to the phase current.

Again??

I'm not clear what you mean by "phase current" vs "line current". Why would they be different in a 3 phase motor? Maybe it's an IEC terminology I am not familiar with though.

Besides, you set the OL relay to the MOTOR NAMEPLATE FLA, nothing else is appropriate. So if the motor says it is 30A FLA, you set the OL to 30A. It's not any more complicated than that.

In a Star-Delta starter however, it makes a different WHERE you hae the OL in the power circuit. If, as in the drawing posted above by kvsridhar, it is in the Star portion of the starter, you set it for 58% of the motor nameplate FLA. If however it is located in the 3 phase supply lines (maybe that is what is meant by "line current"?) then again, 100% of the motor nameplate FLA. Different starter mfrs locate it in different places and sometimes depending on size. For example if the motor s relatively small, the OL is placed in the Star circuit and set for 58% because the OL can be smaller / cheaper. But if the OL is going to ned CTs anyway because of size, many mfrs then just locate the CTs on the incoming line and then set the OL to 100%.

This is a clear example of IEC vs NEMA terminology as you rightly guessed. The motor has to be delta-connecetd to run, and with all six leads brought out so that one can connect it in star and then in delta. With this option being available, why not connect the relay within the delta, so that you can use a smaller relay than if it was in the main line ? Maybe you can use a direct relay where otherwise you would need a CT relay? Maybe more to do with less space than actual product cost ? Just some notional cost savings in real-estate-starved IEC regions perhaps....i can't say really.

Are you really an electrician/engineer ????....

I got masters in Electrical Machines from Syria.

Are you the OP?

If you are why did you post the question, you would know the answer.
Alternatively, again if you're the OP how much did your "Masters" cost? I ask because you certainly didn't learn anything from it.