HV installations - Transferred Earth potentials 1

[FPelec]

Good evening, everyone,
I'm looking for some material related to transferred earth potentials, for an internal training meeting.
In particular, it would be useful for me to find public-domain documents about:
- the practices adopted by other utilities to manage the potential transferred from their facilities to third parties (eg. minimum distances between HV installations and third party grounding systems).
- news about incidents related to potential transferred from high voltage installations.

Any contribution would be very useful,
Thank you
Fpelec

Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[dpc]

Not sure of the desired technical level, but a Google search for "ground potential rise" turned up some good references and some free white papers. In the US, the telephone companies used to be a good source of information on this because their copper phone lines into substations were a big safety concerns. Less of an issue these days.

 

[cuky2000]

_{" Quoting from IEEE Std 80: It is impractical and often impossible, to design a ground grid based on the touch voltage caused by the external transferred voltages. Hazards from these external transferred voltages are best avoided by using isolating or neutralizing devices and by treating and clearly labeling these circuits, pipes, etc., as being equivalent to energized lines."}

To be honest with you, my observation on this issue is that most utilities ignore this issue. However, it is fair to say that there are not many cases of injury reported for this matter. It doesn't mean that the potential hazard is not there....just ignored perhaps for liability or just difficulties to the engineers to identify this issue.

Two scenarios related to transfer potential are been identified: 1) In Inside or the vicinity of the substation and 2) far from the station.

CASE 1- Inside or near the substation fence: In the US, public safety associate with substation ground grid is primarily limited up to 3 ft (~1.0 m) beyond the substation fence. Outside this limit, the often argument to justify safety compliance is that "there as nothing to touch beyond the fence. This is definitely not a thru statement particularly in urban areas with high population density..... _{Fortunately, other unanticipated materials around the station dissipate the effect of the SC current such as reinforced concrete sidewalks, street asphalt, water, gas, and other piping systems that behave as a natural electrode.}[/i]

CASE 2- Far from the station: special cases of transfer potential are recognized such as isolation of railroad track, communication hardwire, metallic piping system, underground cable shield, OH static shield or neutral wires, pipes lines, etc. However, there are not known many follow up by utility and testing groups to positively identify a safety concern.
_{Indirectly related, some utility is implementing the "stray voltage" program to detect issues with ground current mandate by the state Board of Public Utility (PUC)}

 

[ScottyUK]

Here's one UK utility's take on the subject:

http://library.ukpowernetworks.co.u...id+and+Primary+Substation+Earthing+Design.pdf

edit:
Here's a couple more:

https://www.enwl.co.uk/globalassets...335-i2-earthing-design-for-gp-substations.pdf

http://www.dcode.org.uk/assets/uploads/41-24_-_7th_April_2016_as_sent.pdf

 

[FPelec]

Thank you for your replies.
ScottyUK, this sentence, from the last document you indicated, is quite a surprise for me:

" Where such third party fences are present or are likely to be present within 2 m of the substation, one of the options listed below should be implemented to maintain electrical isolation between the two fence systems"

It seems that 2 m are considered sufficient to avoid dangeoreus touch voltage; I would have expected a value closer to 20 than 2 m.



Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[davidbeach]

At 2m nobody is likely to touch both at the same time.

 

[cuky2000]

For this application isolation panel or non-conductive fence may be an option.

See also thread238-246766