OH Neutral wire resistance-Substation Grounding
OH Neutral wire resistance-Substation Grounding
(OP)
To lower the local substation GPR, I have to build a remote grid connected to the local grid by bonding conductor ( 4/0 bare copper).
Underground portion:
I modeled a 100m of this conductor in the software laying beside HV cables to calculate the resistance value of the underground bonding conductor. I assumed the earth resistivity is 100 ohm-m ( I hope this is true assumption)
Overhead portion:
I also need to calculate the Z+ or Z0 for the neutral wire on OH line and add it to the remote grid resistance to calculate the split factor and affect of the remote grid in lowering the GPR.
the question is whether I need to add the Z+ or Z0 of the OH line to the remote grid resistance and underground bonding conductor resistance to calculte the equivalent resistance?
Underground portion:
I modeled a 100m of this conductor in the software laying beside HV cables to calculate the resistance value of the underground bonding conductor. I assumed the earth resistivity is 100 ohm-m ( I hope this is true assumption)
Overhead portion:
I also need to calculate the Z+ or Z0 for the neutral wire on OH line and add it to the remote grid resistance to calculate the split factor and affect of the remote grid in lowering the GPR.
the question is whether I need to add the Z+ or Z0 of the OH line to the remote grid resistance and underground bonding conductor resistance to calculte the equivalent resistance?






RE: OH Neutral wire resistance-Substation Grounding
You need to determine the current split factor between the current injected into the ground and the one travel awy from the substations.
The soil resistivity,the ground fault current(LGF),the electrical system connection and network topology are critical parameter to determine the GPR.
A simplistic approach is to consider a LGF current source connected to ground at one end in parallel to the substation grid resistance. Connect the grid resistance in series with a interconnected cable impedance with the receiving end resistance connected to ground.
The target GPR area will be the voltage through the receiving end resistance.
The grid and receiving end resistances could be measured or calculated following the IEEE Std 80 guidelines or other suitable method.
I hope this help.
RE: OH Neutral wire resistance-Substation Grounding
VOL PAS-100, NO. 3 March 1981.-IEEE TRANS. ON POWER APP.&SYST.S
Also if you can include both grid in a single yard -bordered by a fence or not-you may use the calculation as per IEEE Std 665-1995 IEEE Guide for Generating Station Grounding Annex C Division of current for small interior grids.
RE: OH Neutral wire resistance-Substation Grounding
My though is it depends on whether or not the o/h portion belongs to the source(system) or the grid. If it belongs to the system then you need to include Z+ and Z0, if it belongs to the grid then you don't.
RE: OH Neutral wire resistance-Substation Grounding
I want to use this remote grid to lower the local station GPR value.
My question is whether to use Z+ or Z0 of the neutral wire to perform the calculation and come up with the equivalent resistance.
For underground bonding wire , I used the same software to calculate a resistance of the wire in contact with the soil.
RE: OH Neutral wire resistance-Substation Grounding
Are there other sources of ground fault current than the remote generator station?
RE: OH Neutral wire resistance-Substation Grounding
Jghrist, could you refer me any litreture regarding the issue please?
RE: OH Neutral wire resistance-Substation Grounding
It would be very difficult to calculate the current splits among the different paths with OH, UG cable, and UG ground wires without specialized software. I suggest reviewing available software at http://ww
RE: OH Neutral wire resistance-Substation Grounding
Coming from the Northeast U.S, I have seldom measured 100 ohm-meter soil or found it through software analysis such as RESAP.
The bonds between the grids are only as good as the upper soil in which it is buried. If the soil resistivity layers are favorable (i.e. low), then as one responder suggested you can treat it as one grid. This is generally the case, but I can assume this from here.
I wish you luck.