Earth Resistance

WHAT VOLTAGE? (Sorry for shouting, but this is another electrical question lacking key data.)

[Is there such a thing as a "too good" (excessively low) earth resistance value?]

no need to shout !! yes it is essential data and missing just working inside one factory for 9 years made me think of the 11KV/ 380 to be only voltage level

sorry for that!!

The earthing needs to be sufficient to operate the circuit protective device(s) without damage to the equipment or cabling.

Next!

Tell us, please, what do you think of this value? Surly you have some thoughts on the subject?

Your omission of critical information, and the question itself, lead me to believe that you are in the wrong line of work.

0.22 ohms seems a bit too high, perhaps you should run another plant in parallel to halve the value.

(Couldn't resist. Hey it's down Friday here).

On a serious note, what electrical standard are you working to? I would have thought the earth resistance limits for your particular application would be in there.

The value itself is a little misleading as you don't say where you measured the resistance (distance does play a factor generally, but it depends a bit on what standard your are working to) or what the resistance was previously (if the resistance has jumped since the previous reading it could indicate a potential problem with your earthing integrity, which is a problem).

Can you provide more information including plant location?

And what if these transformers were replaced by 3 MVA, would same earthing 0.22 be suitable?

This statement is worrying as the way I read it (in the context you have used it in) it seems you may not understand how transformers and protective earthing systems work.

Again, can you provide more information please.

Earth resistance is not a fixed value, that you can measure with any precision. It varies with the seasons, with the moisture in the ground. The protection ought to work at any time. Getting thru certification is an entirely different matter, isn't it?

A 0.22 Ohm result is very very good irrespective of equipment. I refer to the xformer

Yes to both questions. Your values are even good for an electronic earth. Congratulations, BRZK

What is this electronic earth? As per IEEE 1100, any seperate electronic earth is IMPROPER.

Is this a ground mount transformer? Is the earth value you refer to from the earth ring that surrounds the transformer? If you are replacing a ground mount transformer with a physically bigger unit then a new earth ring will be needed to keep the touch voltages and step potential voltages in line. Check your local regulations. Also, as the potential fault current will rise with a larger kVA transformer then the cable diameter sizes used in the earth system may need to increase.