Junior Member
Posted May 4, 2019
Would the current injection, during a substation grounding study, operate any relaying?
I’m having a study performed on several substations soon and I am concerned that there may be some type of trip or alarms due to the current injection during the study.
What type of ground testing are you going to be doing?Originally Posted by Eazyeet
NETA Level III
Posted May 7, 2019
Pro Subscriber
In my opinion, it's possible you could trip something depending on the protection scheme and test procedure. All it takes is enough current passing through a ground CT to trigger a pickup or imbalance.
There have been numerous incidents where using a DLRO on switchgear bus has caused a relay to trip. I'd be extra cautious.
Depending on what type of equipment you are using to inject current, the chance of operating a relay are very slim. If it is a DC unit, the current flows from one lead to the ground grid and back to its source. It would have no affect on a CT in its return path. If it is an AC unit, current also flows from one lead to the ground grid and back to its source. There are a lot of paths it may take but the impedance of a power transformer should be enough to block that direction of current flow through the neutral.
I agree a with Secondgen and would exercise extreme caution. If you contact the test set manufacture and explain the scope of the testing they should be able to get you the information that they need. If you are doing a three point fall of potential test I would think you would be ok but with the two point direct method the DLRO is actually using the circuit as a path for voltage and current probe to probe, very small but it is still there, and it could cause an issue.
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