Earthing neutral

Ah by your use of MV,  I think you are not from this continent - this may explain the mis-understandings.

UK practice is not always to combine HV and LV earths - in the days when the rules were simpler, they were combined if the earth electrode impedance is less than 1 ohm, but had to have two electrodes kept well separated and the wiring insulated from each other if the ground conditions mean the electrode impedance too high, one for HV and the transformer case etc, and the LV one for the secondary side neutral. Nowadays the advice is a little changed, so it  requires you to look up the HV fault level, and then decide if the max credible HV fault current into the local earth would raise the local earth voltage to a dangerous level for a dangerous time (normally taken as 400v or so, but depends on the speed of the HV side ADS systems).  This is a bit more lenient than the old 1 ohm rules in some remote places where the HV lines are long, and more onerous to meet in places with more available fault current.

The HV neutral is not distributed, so all our HV/LV transformers are delta on the HV input side and star on the LV output. This allows earth fault detection on the HV lines to be very fast and quite sensitive. (Imagine current transformers and breakers configured to work like an HV side RCD/GFCI )

We also call the centre of a star transformer the neutral point, even if no load connects to it... this may not be helping the conversation.

Ah by your use of MV,  I think you are not from this continent - this may explain the mis-understandings.

UK practice is not always to combine HV and LV earths - in the days when the rules were simpler, they were combined if the earth electrode impedance is less than 1 ohm, but had to have two electrodes kept well separated and the wiring insulated from each other if the ground conditions mean the electrode impedance too high, one for HV and the transformer case etc, and the LV one for the secondary side neutral. Nowadays the advice is a little changed, so it  requires you to look up the HV fault level, and then decide if the max credible HV fault current into the local earth would raise the local earth voltage to a dangerous level for a dangerous time (normally taken as 400v or so, but depends on the speed of the HV side ADS systems).  This is a bit more lenient than the old 1 ohm rules in some remote places where the HV lines are long, and more onerous to meet in places with more available fault current.

The HV neutral is not distributed, so all our HV/LV transformers are delta on the HV input side and star on the LV output. This allows earth fault detection on the HV lines to be very fast and quite sensitive. (Imagine current transformers and breakers configured to work like an HV side RCD/GFCI )

We also call the centre of a star transformer the neutral point, even if no load connects to it... this may not be helping the conversation.