Solar PV farm Earthing

[SS_EE]

Hi All, in one of my project we observe a very high soil resistivity of around 1500 ohm*m from the soil resistivity report, could you please let me know what needs to be done to install a mesh as per IEEE 80 earthing design. Please note this a solar farm of around 500 kW with a 13.2 kV substation. TIA

 

[Hv&Lv]

Hi All, in one of my project we observe a very high soil resistivity of around 1500 ohm*m from the soil resistivity report, could you please let me know what needs to be done to install a mesh as per IEEE 80 earthing design. Please note this a solar farm of around 500 kW with a 13.2 kV substation. TIA

That’s an extremely difficult question to ask on an online forum.
Quite honestly, you need to get with an engineering consultant in your area. The Philippines have a few engineering consultants that are familiar with the soil, and can also perform a quantitative analysis of the effects of lightning surges before a grounding system is developed.

I don’t mean to put you off, it’s just the question you ask will take quite a lot of man hours and site visits to get the answers you seek.

As a utility, we won’t attempt to design our own substation grounding system in-house. We have an engineering consultant firm do that for us. It also relieves you of liability which is a good thing if you are really looking for the answer here on this forum.

 

[electrofelon]

Also I would just add that you need to be specific about what exactly you are trying to accomplish. I would guess that a majority of people in the industry would say a low or a certain resistance grounding system is important, but for many applications it doesn't really matter or provide any benefit. Just because a PV system is large, I don't see that that triggers any special need for low resistance grounding. Yes the substation itself has some specific important earthing detail, but I believe even that is more about an equipotential system not achieving a certain resistance.

But 500 KW is NOT even large. Do you really have a substation on site for this? What exactly do you mean by substation?

 

[SS_EE]

Also I would just add that you need to be specific about what exactly you are trying to accomplish. I would guess that a majority of people in the industry would say a low or a certain resistance grounding system is important, but for many applications it doesn't really matter or provide any benefit. Just because a PV system is large, I don't see that that triggers any special need for low resistance grounding. Yes the substation itself has some specific important earthing detail, but I believe even that is more about an equipotential system not achieving a certain resistance.

But 500 KW is NOT even large. Do you really have a substation on site for this? What exactly do you mean by substation?

Thanks for the reply. As you rightly said, this is a small plant, to be more specific its an off-grid electrification hybrid plant with BESS and DG's, where we need to step-up to 13.2 kV. The 13.2 kV substation has two step-up transformers along with a Medium voltage switchgear panel.

 

[electrofelon]

Thanks for the reply. As you rightly said, this is a small plant, to be more specific its an off-grid electrification hybrid plant with BESS and DG's, where we need to step-up to 13.2 kV. The 13.2 kV substation has two step-up transformers along with a Medium voltage switchgear panel.

This doesn't jump out to me as needing an exceptional grounding system. Presumably the MV transformers will be on a pad, I would just Bond the rebar grid to make a nice CEE. Is someone telling you that you need something specific or some certain ground resistance?

 

[SS_EE]

This doesn't jump out to me as needing an exceptional grounding system. Presumably the MV transformers will be on a pad, I would just Bond the rebar grid to make a nice CEE. Is someone telling you that you need something specific or some certain ground resistance?

Yes, they are requiring a value of Rg < 5 ohms which is impossible with such a high soil resistivity without any additional measures. And at the same time any significant cost will also cause a cost overrun for the overall project. In my previous experiences with designing an earthing grid for much larger MW scale solar farms I have not come across such a high soil resistivity.

 

[electrofelon]

Yes, they are requiring a value of Rg < 5 ohms which is impossible with such a high soil resistivity without any additional measures. And at the same time any significant cost will also cause a cost overrun for the overall project. In my previous experiences with designing an earthing grid for much larger MW scale solar farms I have not come across such a high soil resistivity.

Wow, ridiculous. I hope "they" are the owners and this isn't someone pouring someone else's money down the toilet. Perhaps a chemical ground would be the best way to achieve that arbitrary value.