Oil Refinery near the North Sea, Ex, Ground Grid and maintenance

[Skogsgurra]

What are normal test and maintenance methods for abovementioned Ground Grid?

Buried grid is made up from 70 mm2 Cu in meshes that are 50 - 100 m. Double 95 mm2 Cu running around and connected to the grid. Several ground plates. Down conductors from pumps, blowers etcetera are insulated 70 mm2 Cu.

Salt water mists and acid rain. Cannot find any data showing test results when grid was new and no data from later tests. The plant is 40+ years old now. Process area around 1000 by 1000 m.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

No answer to this basic and, as I thought, basic question in a whole day!?

Does it mean that there are no test methods? Or no specifications? Or that people don't care?

There must be someone out there that knows about ground grid verification. ScottyUK?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

Sorry, first "basic" was supposed to read "important".

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[iwright]

Hi Gunnar,

I can't help you much other than to say we are having the same issue trying to figure out what if anything we should do with the ground grids at our power plants. Much of the grid is buried in concrete so inspection is not an option. Megger and others make 3 and 4 probe test sets that can be used to measure the resistance of individual ground rods or ground cables or measure the resistance of the soil. The concern with using those is that if you have one of the remote probes in the ground far away from the local ground grid and there is a switchyard or generator fault (30kA) what happens to the test equipment and the operator?

Iain

 

[ScottyUK]

skogs,

Not ignoring this question but don't have much to add to when I answered a very similar question that you posted a few weeks ago. I think you'll be able to prove any individual earth wire is connected to the larger grid, but proving the overall integrity of the grid will be bordering on impossible unless it has suffered very serious damage. If there are any opportune civils works underway supporting other activities then it is a good time to inspect the Cad-Welds at the joints and also the general state of the conductors.

I had a look at using fall-of-potential for the power plant I worked at but we would have needed to be 'remote' from the grid - i.e. the test electrodes would have had to be located impossibly far away from the grid. The clamp-on testers tell you whether there's a connection to the buried grid or not and give an idea of whether it is good or bad, but I have yet to be convinced that the numbers on the display equate to real Ohms.