Gas Insulated Substation

Separation of some sort might be helpful for equipment identification, also for if one substation goes up in flames, it doesn't burn up its neighbor.

Local codes may have something to say about this, perhaps risk of flood or earthquake.

Without any detail, such as indoor or outdoor, levels above and below, lateral displacement or superimposed, transformer insulation medium, other risk factors; the elevation obove or below some datum point should be inconsequential.

What does the rest of the <...we...> have to say about this?

From an electrical perspective, there is nothing that I know of that would prevent you from having the different voltage level equipment at different physical elevations, assuming you can make all the necessary physical connections and meet electrical safety clearances. Electrons don't care if they have to flow up, down, or sideways.

As for the physical construction, the factors to consider depend on whether this equipment is in an enclosure/building or outdoors.

In a building, you need to provide access for personnel, for service and maintenance equipment, and probably an overhead crane to lift/move equipment for installation, repair/replacement, etc. You have to consider where control wiring has to run, and how to meet equipment clearances from the structure.

Outdoors you also have to consider things like vehicle & crane access, personnel safety when you have changes of elevation (slopes/drop-offs, etc.), effects of climate (Does it get icy in winter? Water runoff in rainy season?), and other such factors.

But all of this has to go into your design. It may not prevent you from doing what you propose, but it will affect how you design your station.

What about the electrical earthing grid to be provided at 0.5 m below the ground. If the two GIS (of 132 kV and 220 kV) are at elevation difference of say 3 metres.

Best Regards,

You probably need an Electrical Engineer to look at this locally. Hire someone?

Treat each one separately, the depth is to get good conductivity. If one substation has a higher exposure to lightning, maybe not interconnect the arrester earth leads...

What do you propose or suspect will happen with the earth mats/grids? If there is a massive earth fault, where do you think it will go?

It always returns to the source of the power, or the potential opposite, such as a cloud and the earth.

Usually the system protection will open the faulted circuit, or the weakest link conductor in the return path burns clean, or the potential of the cloud/earth equalizes to a level insufficient to ionize the air between.

That's why you may want to keep your transformer arrester ground leads somewhat separated, so the surge on one line doesn't show up cleanly at the other arresters, while in the process of carrying discharge current. A well designed ground grid for each power system should reduce the cross communication between the two systems

I think you missed the point, What difference will a 3m elevation make to an earth mat? What difference is going to be made if the stations are in close proximity to one another? (20-200m for instance). If they are km's away of course it will change, as the soil resistance will change.

If the 132kv is next to a 220kV yard the earth mats will definitely be connected and commoned. No matter what elevation.

I don't want to be in a station that has an earth connection that burned clean.

I think maybe you are needlessly over-analyzing the situation with no facts. Your audience also can be of little help with the ambiguous configuration you present. The resistivity of the soil with respect to the distance to the center of the earth will be unmeasurable in the 3 meter range you are talking. Without details on the configuration and equipment, the soil composition and resistivity, a ground fault may or may not pass through the equipment between the two substations. For instance, if there is a risk of fault current between the two substations, plus walking access between the two, you need to design for low touch and step potentials along the communication path.

Your grounding system carries little to no current under normal conditions. If you drop a line conductor on to the ground, then it may conduct back to the power source, it may not, depending on many different conditions that you have not considered.

The method you use to interconnect the adjacent ground grids should take into consideration the possible fault locations and types, and you will generally want to avoid direct interconnection (copper to copper) of your lightning arrester ground leads, for example. If your grounding is correctly designed, it will be unnecessary to interconnect them other than the earth between them.

If the line drops on to the structure supporting your insulators, the current will flow back to the source directly through the copper or concrete electrodes and bonding you have designed, the short term current rating is sized to allow full possible fault current and clearing before melting. That design is what will prevent your system from burning your ground conductor clear. However, it is possible and probable under some conditions, one of your ground connections will fail. You need to consider that in your design as well.

Original hypothetical question: 'What about the electrical earthing grid to be provided at 0.5 m below the ground. If the two GIS (of 132 kV and 220 kV) are at elevation difference of say 3 metres.' (10 feet)

I am now intrigued as to why an elevation of 3m (9.89feet), would make a significant difference on an earth mat in any substation/switchyard?

Well obviously the lower substation will naturally have better lightning protection since the upper substation will be the lightning rod for the area.

How you wish that were true. We may as well have chocolate teapots or a trap door in canoes.

Will the canoe trap door be how Hiawatha gets into his shallow draft submarine?

It will go through a circuit protection device, which will disconnect it.

Earthing can be improved by releasing a large quantity of seawater over the earthing mat.

That improvement is a bit fishy.

Just because Physics says you can do something, it doesn't mean that one should do that thing.

This all depends on what electrical codes should be followed. Determining which electrical code should be followed requires knowing where this installation will be placed.

Anonymous Poster Land is an exceptionally large place...

Is this 220KV primary, onto a Tfx of secondary 132kV? Is this for a harsh environment where the GIS is indoors as GIS outdoors would be a total waste of investment. What are the limitation on using Air Insulated bars?

Many stations are build on two levels, it all depends on the Geotech results and cost of remediations, if its level or terraced.

Your poorly worded question here, will draw poor results and misleading information.

"IF we have..", then you say "we intend to.." It makes me doubtful of your facts.

If you build your station on a slope, put the 220 above, and the 132 below, gravity will assist the flow of electrons, as it is all downhill.