Ground Grid Resistance Measurement On A Live Substation

You should do some research!

A practical guide to earth resistance testing - Weschler ...

FOP vs SGM Ground Impedance Tests

High Voltage Substation Earth Grid Impedance Testing ...

Also you can do some research on youtube. In about a week we are going to add half dozen instructional videos for Lineman. A few are safety like all the rubber matts and guards you need to use and how. See/subscribe to our channel BIN952. We have a total of 20 new videos to release there, working on 21 right now.

The fall of potential method is suitable for live installations.

Megger have published a PDF on the subject.

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.

Ask for a Method Statement and a Risk Assessment, and have these two documents approved and to hand before setting off to the <...substation to meausure the grid resistance...>. After all, whoever asked for the task to be carried out can see the installation, and nearly every other CR4 reader cannot.