Ground Cable Integrity Testing
Ground Cable Integrity Testing
(OP)
What is used for testing substation, and other, ground cables for their resistance/integrity? I don't mean the earth resistance grid testing but testing individual ground cables into the ground and up the structures? Is this test routinely performed? Thanks






RE: Ground Cable Integrity Testing
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Ground Cable Integrity Testing
RE: Ground Cable Integrity Testing
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Ground Cable Integrity Testing
Are you simply wanting to confirm the ampacity of the guage of cable you have? I've never heard of this being done before. If you buy a 4/0 stranded conductor, trust the datasheet. If it doesn't look physically damaged, then it isn't. Test the bonding points (at the structures and the ground grid) with a resistance check. If the bonding points were for circuits that normally carried current you could use thermal imageing at the bonding points to see that they are good (not too hot). Ground grids shouldn't normally carry any significant amount of current. When a fault does happen and they have to marshal many kA's of current we rely on the protections to stop the current flow. If the protection fails to do this than you have much more than just a damaged ground grid to worry about. Testing conductors/bond points with 50A does not come close to simulating a fault condition. Also, make sure the proper connecting hardware is being used for the size and type of ground conductor you choose.
RE: Ground Cable Integrity Testing
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Ground Cable Integrity Testing
RE: Ground Cable Integrity Testing
We prefer to do a measurement that takes all these circumstances into consideration and produce real results, like 18.7 milliohms instead of a fictive and false value like 567 milliohms or thereabout.
Sorry that you haven't heard of the method before. Now you have.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Ground Cable Integrity Testing
RE: Ground Cable Integrity Testing
First of all it is not important how precisely will be it is actually an average and it is not any indication of the local actual temperature.
In my experience with tens of thousand power cables in duct banks I never came across with cable overheating .Of course, in a power station it is permissible to oversize a bit the conductor cross section.
For instance the DIN/VDE 276 standard takes into consideration a 0.7 load factor usually, calculated from the 24-hour load cycle, also.
Even if it is a constant load considered , in my opinion ,the earth temperature changes in a day time and the transient constant of cable temperature variation in a duct bank is high [high inertia with respect the changes].
However the cable laid directly in the ground was overheated and damaged often. I think here is the problem of earth uncontrolled drying around the cable.
RE: Ground Cable Integrity Testing
The OP asked:
"What is used for testing substation, and other, ground cables for their resistance/integrity?"
In a ground grid the resistance of a 2/0, 4/0 or larger cable which has been properly sized for the calculated fault current is immaterial compared to an anomalously high resistance caused by a corroded joint or cable.
A high resistance point in a ground grid has at least two implications:
1. It may not limit step and touch to the calculated safe levels.
2. It may fuse open under fault conditions with the result that step and touch voltages are even higher.
VLFit; I suggest that for the best answer to your question, you read over thread
thread238-384792: Grounding Grid: Grounding Grid
and follow the link to Gunnars presentation at:
http://www.gke.org/presentationer/files/Low%20ohms...
Bill
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"Why not the best?"
Jimmy Carter
RE: Ground Cable Integrity Testing
There are two-basically-ways to build a grounding grid: bolted connection or cadweld[or brazing] connection.
The advantage of the cadweld mode is the elevated permissible temperature[for copper conductor up to 1060 oC, instead of 250 for bolted connection].The vertical electrode connection does not need a handhole [visitable].
The bolt connection grid is provided with handholes in order to connect the electrode.If you will open the connection between two adjacent handholes you may test the ground cable connected with.
However,in my opinion, it is not required if the touch and step voltage will be in the permissible limits[see IEEE 80/2000].
RE: Ground Cable Integrity Testing
I did this at a remote cable terminal station and found the grounding cable hardware loose enough to move when I gave it a boot with my foot. Lots of loose ones. Turns out the protection hardware was failing for years during transients on the DC transmission system. Construction went back to the site and after repairs (probably just tightening) no more P&C worries.