Grass Growth in Substations

[mbrooke]

Does grass growing in a substation present any hazard to worker safety? Does it change the way a substation needs to be designed ie the ground grid? I guess I'm looking for re-assurance. :angel:

 

[mbrooke]

This:

 

[gadfly56]

Well, speaking from an abundance of ignorance, what are the potential (sorry!) risks?

 

[mbrooke]

Well, speaking from an abundance of ignorance, what are the potential (sorry!) risks?

Lowering foot resistance and theoretically (guessing) bringing remote earth into the station if the roots reach below the ground grid.

 

[junkhound]

It is all part of the green power revolution. Every source feedng the substation is solar or wind. Note: hydro does not count, it destroy fishies.

 

[mbrooke]

It is all part of the green power revolution. Every source feedng the substation is solar or wind. Note: hydro does not count, it destroy fishies.

But how does the grass play into all that? It still lowers resistance.

 

[iceworm]

All I have seen have gravel - usually pea gravel or washed river rock ~1/2"
IEEE 80 Safety is AC Substation Grounding, is a good place to look.

7.4 Effect of a thin layer of surface material
Equation (14) is based on the assumption of uniform soil resistivity. However, a 0.08 m to 0.15 m (3 in to 6 in) layer of high resistivity material, such as gravel, is often spread on the earth’s surface above the ground grid to increase the contact resistance between the soil and the feet of persons in the substation. The relatively shallow depth of the surface material, as compared to the equivalent radius of the foot, precludes the assumption of uniform resistivity in the vertical direction when computing the ground resistance of the feet. However, for a person in the substation area, the surface material can be assumed to be of infinite extent in the lateral direction.

If the underlying soil has a lower resistivity than the surface material, such as clean large rock with wet resistivity in the thousands of Ω-m, only some grid current will go upward into the thin layer of the surface material, and the surface voltage will be very nearly the same as that without the surface material. The current through the body will be lowered considerably with the addition of the surface material because of the greater contact resistance between the earth and the feet.

12.5 Use of surface material layer
Gravel or surface material coverings, usually about 0.08 m to 0.15 m (3 in to 6 in) in depth, are very useful in retarding the evaporation of moisture and, thus, in limiting the drying of topsoil
layers during prolonged dry weather periods. Also, as discussed in 7.4, covering the surface with a material of high resistivity is very valuable in reducing shock currents. The value of this layer in reducing shock currents is not always fully realized.

You will want to read the rest of it.

Editor will not let me put this line at the top:

All I have seen have gravel - usually pea gravel or washed river rock ~1/2" ~ 6" deep​

 

[iceworm]

Ok I'm thoroughly ????

I have this line both at the top of the post and the bottom. I can't see it

All I have seen have gravel - usually pea gravel or washed river rock ~1/2"​

 

[mbrooke]

All I have seen have gravel - usually pea gravel or washed river rock ~1/2"
IEEE 80 Safety is AC Substation Grounding, is a good place to look.






You will want to read the rest of it.

Editor will not let me put this line at the top:

All I have seen have gravel - usually pea gravel or washed river rock ~1/2" ~ 6" deep​

Thats my point though, the grass contradicts all that. So how is it acceptable? :blink:

 

[iceworm]

(*&%&$&^()*_*^#@@! Editor

Maybe this one will do it if you add the three posts together.

In my total experience - that would be a whopping two, we used a geo-cloth over the soil, with 6" of gravel on top. Local soil is really fine, turns to gooey muck (engineering definition please) when it gets wet. The geo-cloth keeps the gravel from disappearing into the muck after the first couple of heavy rains.

 

[mbrooke]

(*&%&$&^()*_*^#@@! Editor

Maybe this one will do it if you add the three posts together.

In my total experience - that would be a whopping two, we used a geo-cloth over the soil, with 6" of gravel on top. Local soil is really fine, turns to gooey muck (engineering definition please) when it gets wet. The geo-cloth keeps the gravel from disappearing into the muck after the first couple of heavy rains.

I'm just seeing symbols...

 

[iceworm]

Thats my point though, the grass contradicts all that. So how is it acceptable? :blink:

I'm thinking it is not

 

[mbrooke]

I'm thinking it is not

Would a more intensive ground grid mitigate the effects of the grass?

 

[iceworm]

I'm just seeing symbols...

That is just me having an internal discussion about the heritage of the author of the editor

 

[iceworm]

Would a more intensive ground grid mitigate the effects of the grass?

Nope. As I understand IEEE 80, the installation is a relatively conductive layer (Ground mat existing soil fill) with a relatively non-conductive layer (the gravel) on top

 

[mbrooke]

Nope. As I understand IEEE 80, the installation is a relatively conductive layer (Ground mat existing soil fill) with a relatively non-conductive layer (the gravel) on top[

But in theory if your bottom layer is more conductive, you will get better equal potential and less need for a top insulator?

 

[mbrooke]

That is just me having an internal discussion about the heritage of the author of the editor

You mean the site programmer for V bulletin 5? I'm having issues of my own with the forum.

 

[iceworm]

Just a suggestion:
Time for you to read IEEE 80

 

[mbrooke]

Just a suggestion:
Time for you to read IEEE 80

Is there any part in IEEE that lets you have grass?

 

[iceworm]

You mean the site programmer for V bulletin 5? I'm having issues of my own with the forum.

No, just the editor portion