Substation Earthing
Substation Earthing
(OP)
Any advice where I can source (BS's/Standards etc) the earth value of a sub-station. My thoughts are that it should be less than 1 ohm, but getting conflicting reports that it can be up to 5 ohms???
Also being advised that a common earth can be used, being linked between sub-stations. Surely if this is the case and a cable is isolated/disconnected no protection is then provided.
Also being advised that a common earth can be used, being linked between sub-stations. Surely if this is the case and a cable is isolated/disconnected no protection is then provided.






RE: Substation Earthing
Many utilities companies adopt similar criteria than the IEEE Std 80 for a go/no-go test after installation is completed.
It is good idea to interconnect neighboring substations to maintain a uniform potential in the areas. Many design call for insulated cable if is routed in area with low resistivity such as native soil or concrete slabs where there is a good chance to exceed the allowable step and touch potentials
The use of insulated interconnecting conductors may not be necessary if insulating surfacing materials such as crushed rock or asphalt is provided between the interconnected substations.
RE: Substation Earthing
RE: Substation Earthing
Rg = (ρ/4)·sqrt(π/A)
where ρ is in ohm-m and
A is in m²
(IEEE std 80-2000 eq. 50)
Using this, a 100' x 100' grid in 100 ohm-m soil would have a resistance of around 1.5 ohms.
RE: Substation Earthing
RE: Substation Earthing
Here is what IEEE-Std 80 say about resistance.
RE: Substation Earthing
we start it from back we get GPR and step and touch potential and see the value of resistance and if we realize that this value is not good. we need to reduce it. Saying that for distribution is < 5 ohms, it works but again we have to make sure the potentials are with in limits.
cheers !
RE: Substation Earthing
A good ground design should satisfy the entire safety requirements. This include not only the GPR (resistance)but also the prospective step and touch potentials must be less than the allowable design values.
Although there is a way to perform actual field tests of step and touch potential, only few utilities perform this test routinely opting to measure the ground resistance unless there are large discrepancies with the calculated values.
Here is additional information in this subject. htt
RE: Substation Earthing
ENA S34 also provide useful assistance for UK applications
IEC 61936 provides guidance for HV substation applications
IEEE80 Also refers