I came across a post about nitrogen filling for liquid-filled transformers, but one question wasn’t addressed: Can this procedure be performed on an energized transformer?
The reason I’m asking relates to transformer liquid sampling. In a recent course, I learned that sampling should never be done under negative pressure. ASTM D-923 states not to sample under negative pressure and provides a method to determine if negative pressure exists, but it doesn’t offer guidance on introducing positive pressure. It almost reads that you should abort the liquid sample.
During the course, they mentioned that if negative pressure is present, you should fill the transformer with dry nitrogen to raise the pressure to an acceptable range (typically 1–3 PSI).
So my questions are:
- Can this nitrogen filling be done while the transformer is energized, assuming there are no issues and you have the proper valves (e.g., purge valve/nitrogen fill valve), tools, etc.?
- If yes, what is the typical procedure?
- Are there any standards or documented practices you’re aware of for performing this work?
Obviously, it makes sense that doing any work on a transformer is best and safest when performed de-energized, however, sometimes that option is not easily available to do; just like conducting liquid sampling, they introduce external sampling ports so it can be done when the transformer is energized.
Let me know what you all think!
