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Join Date: Aug 2014
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Ground Grid Resistance Measurement On A Live Substation

08/29/2014 12:50 PM

I have to go to a substation to meausure the grid resistance, the thing is the substation is energized (not sure how to say it in english, I mean to say that i have voltage in the primary circuit).

is it possible to use the 62% method under this circunstances? if not, what should i do?

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#1

Re: GROUND GRID RESISSTANCE MEASUREMENT ON A LIVE SUBSTATION

08/29/2014 1:37 PM
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#2

Re: GROUND GRID RESISSTANCE MEASUREMENT ON A LIVE SUBSTATION

08/29/2014 3:40 PM

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#3

Re: GROUND GRID RESISSTANCE MEASUREMENT ON A LIVE SUBSTATION

08/29/2014 5:31 PM

The fall of potential method is suitable for live installations.

Megger have published a PDF on the subject.

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#4

Re: GROUND GRID RESISSTANCE MEASUREMENT ON A LIVE SUBSTATION

08/30/2014 10:21 AM

Almost every ground grid that I tested was involved in an energized substation or manufacturing plant. I never had any problem with the issue most worried about in this testing. That of a ground grid that was not really tied to ground but somehow had leakage current to it, raising the voltage of the grid above ground potential. While theoretically this is possible, it would be very rare. We mainly interviewed the customer carefully and noted any abnormalities and the reason for the test. Usually it was for data and complying with local codes or insurance companies. We were careful, but never ran into problems. Most of the problems were with lack of soil moisture and sometimes grounding had to be improved a little, but we never encountered a total grid that was floating, and that is unlikely. The other point is that the test stakes are not all that good of a ground and there would be a lot of resistance in the circuit while testing. Ground testing is interesting and the methods puzzling at first, but once you study it, it is facinating to see how the tests work out to be very accurate.

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