Nitrogen filling for liquid filled transformers?

I recently joined another NETA testing company.
Of course everyone has their procedures and their ways of doing things. In the few months here I can say I’ve learned some useful and cool tricks to the trade.
My question to the community is- does it matter at what pressure you fill, say a pad mount transformer, with nitrogen. At my old company, we’d typically just “send it” at approx. 100-150PSI where we’d get to 2PSI fairly quickly. New company seems pretty adamant about filling at a slow steady pace of 10PSI. Just trying to see the reason as to why.
SECOND QUESTION. What would be the reason you would want to have your nitrogen pressure at 2PSI before doing any electrical testing. The only reasoning I got was “I was taught this way so that’s how we do it”. I do not operate by that mind set and I need a reason or else I feel as if I am an unknowing participant in that monkey and the latter experiment. I come to you all as I cannot find anything online. Thanks in advance.

1 Like

This is a good question, I think most of us do things because that is the way we were taught. It has always been my practice to pressurize the tank to approximately 2PSI because this allows for some weather variation without potentially triggering an overpressure.

I believe there is an IEEE standard that references 2 to 5 psi as a recommendation but I cant locate it right now.

10 PSI seems like way too much. For new transformers maybe this would serve as a stress test. Filling it above 5 could eventually raise close to 10 depending on the outside atmosphere.

You want pressure in the tank to avoid any potential flashovers when doing electrical tests. Also for oil samples so you don’t draw air into the tank.

From Megger:

Never perform electrical tests of any kind on a unit under vacuum. Flashovers can occur at voltages as low as 250 volts. (see attached)

Transformers_AG_en_V01.PDF (104.6 KB)

Thanks for the input.
Just to clarify, I was talking about the regulated pressure on filling the tank. 2PSI on being the end result of both methods.