Ground Impedance Testing

[africanamber]

Hello - Our company purchased recently Omicron test set for us to perform Ground grid assessment, line impedance and Step and Touch. We have really only just begun the full capability of the test set, which works very nicely but had questions on Point to Point values and what is acceptable...I believe within a Substation of 115kv size, the ground impedance may only be required to be no more than 5 ohms, but I am not directly measuring the ground I am measuring from my reference point to another known point within our sub (Breaker GND, Switch GND and so forth). So what is actually permissible? We measured .5 milli ohms on average with injecting 100 amps, mind that the Sub is approx 300'X900'. I appreciate any comments regarding this Post. Thanks

[Sanjayo]

Hello - Our company purchased recently Omicron test set for us to perform Ground grid assessment, line impedance and Step and Touch. We have really only just begun the full capability of the test set, which works very nicely but had questions on Point to Point values and what is acceptable...I believe within a Substation of 115kv size, the ground impedance may only be required to be no more than 5 ohms, but I am not directly measuring the ground I am measuring from my reference point to another known point within our sub (Breaker GND, Switch GND and so forth). So what is actually permissible? We measured .5 milli ohms on average with injecting 100 amps, mind that the Sub is approx 300'X900'. I appreciate any comments regarding this Post. Thanks

From what I can tell you are using the set for point-to-point DLRO at 100A to verify continuity between equipment. Average values of 0.5 milliohms (500 microhms) are good numbers in my opinion. Depending on the distance between equipment higher readings may still be acceptable.

[africanamber]

From what I can tell you are using the set for point-to-point DLRO at 100A to verify continuity between equipment. Average values of 0.5 milliohms (500 microhms) are good numbers in my opinion. Depending on the distance between equipment higher readings may still be acceptable.

Thank you Sanjayo. I appreciate your input.