If Nitrozen Filled In Power Transformer For More Than 6 Months During Stroge

Nitrogen is an inert gas. It used to keeps moisture out. As long as the transformer is sealed there should not be any problems. You might purge every so often to keep interior dry.

Other members may have more information that may help.

Hi,

If the enclosure is air-tight and purged with nitrogen once, why is it necessary to purge every often?

If enclosure is air tight and purged no problem. Just have a gauge or some means to verified that conditions have not changed.

Confused. are you talking about removing ALL the oil and replacing it with gas or just topping off the transformer with gas?

I believe that he is unsure of problems related to using nitrogen in his transformer. In industrial transformers, we use nitrogen to keep out moisture. General practice calls for the nitrogen pressure to be maintained from approximately 1 psig to 5 psig. Overpressuring can push oil out vents in some configurations. He should be concerned about this. As to his use of nitrogen, it is a good thing to use and should be kept in his transformer during storage of the transformer.

Hi,

Am I wrong in assuming that Anandkumar is talking about storage only? Also, he may be talking about dry type transformer only. If it was oil filled, wouldn't oil keep moisture out? Or, if oil filled, are you worried about moisture trapped (Since not soluble) in oil?

I am speaking about power transformers used in the power industry. In service, they have a maintained nitrogen pressure. Out of service, they are also maintained with nitrogen pressure. If overpressured, they will relieve pressure through a vent (relief valve), or can relieve through unexpected leaks in the system (i.e. flanges, etc.).

His original question was about any problems with using nitrogen. I am assuming he is talking about large power transformers which have oil in them for cooling. The oil will expand as the transformer gets hot and as such can leak. With use, these transformers can develop leaks which if too low pressure can have air in-leakage. If this occurs, moisture can develop in the oil. Nitrogen is maintained as a blanket or inert barrier to avoid this situation.

If the oil gets moisture in it, it can decrease the reliability of the transformer.

In answer to his question, he can maintain nitrogen in the transformer without problem for an indefinite period of time in storage.

Thank you RG2.

OK Correct me if i'm wrong, but usually high power transformers have a header tank, associated pipework with a Bucholts valve in the pipework to the header tank, indicating that the main body of the transformer is FULL.

There would also be a sight glass containing silica crystals to absorb moisture.. hopefully!

surely if the transformer has a header tank then the main body is FULL of oil, if so then why do you need to fill the transformer with gas to prevent the ingress of moisture.

Moisture is created by the warming and condensing of air. As this transformer is not is service it is not producing heat, so logically it will not produce moisture, if it ever did at all, and any other moisture would be absorbed by the silica.

If it has a header tank, then fill the header tank to the brim, seal the filler cap and be done with it.

Which ever you decide to do, you should before installing this transformer if it has been in storage for any length of time, complete a full test on the transformer, TTR test, AND a di-electric test on the oil, regardless of how you have stored it.

What you say is indeed true, but not in every case. We have some of the type you describe and we also have others which are older and are configured without the silica crystals. The ones without the silica crystals are not configured with the reservoir, Bucholts valve, etc.

An oil filled transformer has some space that is filled by nitrogen to allow for the variations in temperature to be absorbed by the compressibility of the nitrogen. With no expansion room, the expansion of the oil with T would cause extreme pressures = fracture.

The wires must enter through sealed insulators. The bond between the wire and insulator and between insulator and case can also experience differential forces with temperature changes. If these changes, which may be a daily cycle, cause a fatigue fracture path to develop then oil can exit or air/moisture can enter, which must be avoided. With excess pressure in the transformer any small leak will pass fluid more rapidly and in time the pressure will fail and cyclic 'breathing' will occur - which can lead to failure.

External inspections by drive-by are done from time to time. Some modern units have pressure and temperature data sent by radio or over the line for a central watch.

Thanks RG2 & Aurzion, you both filled in on my thoughts. The nitrogen is inert, helps keep moisture out. Monitoring can be as simple as a sight glass to radio link for remote measurements.

As to storage "Non use" even with no oil inside purged with nitrogen there should not be any problems.

Now if a transformer with oil is stored, as long as there no contamination of the oil and the air head space is purged with nitrogen there should not be any problems.

Now if the oil has contaminants that could cause problems in any conditions storage or use.

If the oil is drained, it must be evacuated to re-fill, or bubbles will form in the coils. Those bubbles can lead to breakdown and discharge if the voltages are high enough. The oil too must be "boiled" out by heating under low vacuum pressure prior to filling the transformer.

It's more trouble to drain and store than it is to keep it full and purged with Nitrogen. And like other posters have said, the pressure should be only a pound or two above atmospheric pressure at the most.