Small Substation Grounding
Small Substation Grounding
(OP)
We are very successful using WinIGS to design our substation grounding systems to comply with IEEE80. However, on small substations (80'X 80' square) we cannot get the touch and step potentials to be lower than the allowable. Small areas tend to have this problem regardless of how much additional horizontal copper or ground rods we install. Any solutions to getting small substations to meet IEEE80? Worst case we think would be to install an expensive grounding well. Other solutions?






RE: Small Substation Grounding
http://www.erico.com/public/library/fep/LT0359.pdf
A lot of vertical electrodes [90-100] of 3/4" dia and 50 ft long you have to drive all around the substation area.The distance between the horizontal electrodes would 15-16 ft.
Of course crushed stone of 3-4" height is required.
Also the Grounding Grid has to be extended 3 ft outside the fence [and the fence has to be grounded if you cannot isolate it].
If the soil resistivity is high the problem is more complicate, of course.
RE: Small Substation Grounding
In case you have buildings, try to using structural electrodes (dedicated steel mesh 5mx5m in reinforced concrete floor, wire wrapped to re-bars for electrical continuity & finally brought out to be connected to your earthing system). See pic on http://
This should provide better control of touch & step voltages by making the floor more equipotential.
Near corners of the fence you could try to install pre-made Cu meshes (1.5m x 1.5m, Furse supplies something similar) at shallow depth.
RE: Small Substation Grounding
RE: Small Substation Grounding
RE: Small Substation Grounding
-Use breakers with shorter clearing times
-Import soil of lower resistivitity
-Drive ground rods deeper (I heard of a company on this forum claiming they could get 100' in bed rock)
-Use Erico GEM ground enhancing material
Is it allowable or possible to extend your grounding system beyond the fence to give you a greater area?
Just some ideas.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Small Substation Grounding
In the first instance, the actual resistance may be larger and there may be more current split. In the latter instance, how do you change the soil model to correct for the resistance measurement? A change in overall resistivity may not reflect the actual case. If the soil actually has a lower layer with lower resistivity, lowering the resisitivity of all of the soil may give an unconservative calculation of touch-voltages.
RE: Small Substation Grounding
RE: Small Substation Grounding
How did you measure the grid resistance with the neutrals connected? There are ways to do this, but it will be difficult to get outside the zone of influence of the ground system with a simple fall-of-potential measurement.
RE: Small Substation Grounding
Maybe adding 2-4 deep rods will drop your resistance.
RE: Small Substation Grounding