Dry Air Filling in Transformer

Cheaper, but I am not entirely sure I understand your question:

1. Tank is filled or transformer or what?

2. dry air INSTEAD of N2?

3. Do you mean it is filled with something else after it arrived on its final destination or after it is manufactured and before it is send to final destination?

That's probably the only other advantage besides the slightly cheaper costs to fill it with dry air.

No moisture.

Air is already 78% N2 anyway.

Read that little book that came with the transformer and fill with whatever it says to use.

Thanks for the reply guys...

@ideasmith: (this is what i know) main oil tank of large power transformers when dispatched from manufacturing site to installation site is filled entirely with dry air or nitrogen, as the weight of oil filled transformer will be too much.

So are there any other specific reason to select dry air in place of N2 than safety related issues with N2?

Contact with Oxygen in dry air doesn't do any good to the cellulose paper insulation.

That is the reason we take pains to eliminate oxygen coming in contact with transformer oil/insulation, such as use of air bag in the conservator, use of nitrogen capping at the top in sealed transformers (smaller ratings).

Very strongly suggest that you get someone from the factory to assist you. There are certain procedures that you must follow when purging and filling the tank with oil. If you do not do them in the proper order and timing sequence then you risk having trapped pockets of gas in the insulation which will release copious quantities of "magic smoke" the first time it is energized, rendering the transformer useless.

Atmospheric gas mix is 80% Nitrogen. 19% Oxygen and 1% other gases. While you might think Dry Air Mix pressurization of a transformer might exclude humidity, the reason for using Nitrogen is simply to exclude any oxygen which after heating and cooling causes oxidation on all metal surfaces and corrosion effects. If you use a dry air mix, which by the way has to be pressurized, you run the risk of diluting the oxygen content of the mix into the oil, degrading its insulation properties and furthermore introducing a highly oxydizing agent which is not inert and under high temperature reacts with all metallic and other chemicals inside the tank. Pressurized Nitrogen is used for this purpose because it is practically inert, non-conductive and very cheap. This is standard procedure for this type of practice.

From an ABB Transformer Installation Manual:

"...Closing the Transformer and Final Dewpoint Measurements

After the assembly has been completed, remove all the tools and working material from the transformer, seal the transformer and pressurize with dry air or nitrogen to 20 kPa; 3 PSI (.2 bar)..."

The phrase "...dry air or nitrogen..." occurs repeatedly in these instructions except, of course, when the tank is to be entered for inspection, then it's "...dry air must be used...".

Both dry air and nitrogen need to be pressurized, otherwise when the internals cool down enough for the tank to go to a vacuum, (moist) outside air will be drawn in through the smallest openings.

That's why we RTFM (Read The Fine Manual) every time we get a piece of equipment.

It is easier to get dry nitrogen instead of dry air. You get it either in bottles or as a liquid in bulk, and there is next to no moisture in it. Also, when you use nitrogen, there is no possibility of inducing corrosion in the stuff it comes into contact with. So your best bet is to use dry nitrogen.

Unless you want to get into the space. See Rams post 2#