Gas in power transformer

[PeterJ007]

Update - transformer did not trip overnight although oil level did drop a little.
Decided not to top-up oil as planned but to see what happened during the day
No low-oil trips during the day!!
Will try to add a little oil tomorrow morning

 

[GoldDigger]

If the cause of the level reduction does indeed involve a trapped air/gas pocket within the transformer, it will eventually be necessary to add oil if the pocket slowly dissolves in the oil and dissipates.
In the meantime, one concern would be the lack of cooling wherever the pocket or pockets are located.

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[PeterJ007]

If the cause of the level reduction does indeed involve a trapped air/gas pocket within the transformer, it will eventually be necessary to add oil if the pocket slowly dissolves in the oil and dissipates.
In the meantime, one concern would be the lack of cooling wherever the pocket or pockets are located.

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Indeed GoldDigger - we're monitoring gas temperature every half hour at the moment.
Another concern I have is that if we add oil and the building gas bubble cannot escape (through the DMCR) - will that lead to an over-pressure trip? And, if so , how will we relieve that?

 

[zbang]

If there is a gas bubble then a vacuum pump ought to pull it out. Might be something to consider, anyway.

 

[PeterJ007]

If there is a gas bubble then a vacuum pump ought to pull it out. Might be something to consider, anyway.

OK - thanks zbang. If our only access to the oil is via the DMCR will a vacuum pump draw out air or oil?

 

[Hv&Lv]

OK - thanks zbang. If our only access to the oil is via the DMCR will a vacuum pump draw out air or oil?

It will pull oil if you vacuum too long.
I can pull full vacuum on a transformer and get no oil but then I have a 14” blanket to work with.
Full vacuum will pull the oil up a couple of inches

 

[PeterJ007]

It will pull oil if you vacuum too long.
I can pull full vacuum on a transformer and get no oil but then I have a 14” blanket to work with.
Full vacuum will pull the oil up a couple of inches

OK - a gentle suck will draw out the air - a bit like drawing methane out of a landfill!!

 

[GeorgeB]

It will pull oil if you vacuum too long.

Full vacuum will pull the oil up a couple of inches

I've read and read again multiple times, and am puzzled. Oil air interfaces are common things in hydraulic systems. Applying vacuum to de-air and de-water hydraulic (petroleum) oil is a common thing. Dissolved air and water are all too common and cause all sorts of problems in "my" equipment, BUT I'VE NEVER seen the volume of oil change measurably. Pump inlets and cavitation wreak havoc. Flat tank sides flex and sight gauges show increase, yes. Enough vacuum for the oil to "boil", yes. But can you provide a link explaining the physics of what is being described?

 

[GoldDigger]

I've read and read again multiple times, and am puzzled. Oil air interfaces are common things in hydraulic systems. Applying vacuum to de-air and de-water hydraulic (petroleum) oil is a common thing. Dissolved air and water are all too common and cause all sorts of problems in "my" equipment, BUT I'VE NEVER seen the volume of oil change measurably. Pump inlets and cavitation wreak havoc. Flat tank sides flex and sight gauges show increase, yes. Enough vacuum for the oil to "boil", yes. But can you provide a link explaining the physics of what is being described?

I think we are not dealing with dissolved air but rather with an air pocket within a complex shape in the core or case of the transformer. Created when just fillint the interior with oil will create a closed at the top air pocket as the oil level rises. The standard way to deal with this is to pull a vacuum on the interior before the oil level reaches your highest access point.

Different process from bleeding a braking or other hydraulic system, but the same underlying problem.

Pulling a vacuum increases the volume of the air bubble sufficiently that most or all of the air escapes the trapping volume. Any remaining air is compressed to a harmless volume when pressure is reapplied.

 

[winnie]

But if there is such a trapped bubble in a filled transformer, then when you pull a vaccum the bubble will expand and displace oil.

Jon

 

[GoldDigger]

But if there is such a trapped bubble in a filled transformer, then when you pull a vaccum the bubble will expand and displace oil.

Jon

True, until the continuing overflow from the bubble floats to the top. At that point the oil level goes back down and when you release the vaccum the residual air pocket compresses and the oil level goes down to below the previous low point.

 

[PeterJ007]

Update: Oil level had fallen during the night but not enough to trigger the DMCR. We added 4 liters of oil and the transformer ran all day again with no trips.
Fingers crossed here!

 

[Hv&Lv]

I've read and read again multiple times, and am puzzled. Oil air interfaces are common things in hydraulic systems. Applying vacuum to de-air and de-water hydraulic (petroleum) oil is a common thing. Dissolved air and water are all too common and cause all sorts of problems in "my" equipment, BUT I'VE NEVER seen the volume of oil change measurably. Pump inlets and cavitation wreak havoc. Flat tank sides flex and sight gauges show increase, yes. Enough vacuum for the oil to "boil", yes. But can you provide a link explaining the physics of what is being described?

I’m only talking about a tiny air space here in his transformer.
You pull vacuum from the relay and pull the little bit of air out as the tank compresses from the vacuum the oil has to go somewhere- out.

on a large station XF (15-30 MVA) when you pull vacuum down as far as possible you will see a difference in the gauge. It may be as small as a 1/4 inch on the gauge.

Link for the physics? Sorry, just going by experience in this one

 

[PeterJ007]

Two more days with no low-oil trip. A little gas had to be released from the DMCR but no trips!!
Fingers still crossed

 

[PeterJ007]

Another two days without a low oil level trip. Still seeing some gas generated, which is vented from time to time.
I like the outgassing theory - maybe it's coming to an end at last!

 

[Hv&Lv]

Another two days without a low oil level trip. Still seeing some gas generated, which is vented from time to time.
I like the outgassing theory - maybe it's coming to an end at last!

More than likely a pocket of gas in the top and when the transformer heats and expands the gas goes somewhere.
Now that you’ve let enough of the excess air (gas, whatever) out there should be a partial vacuum on the transformer.
The little bit your getting now is still due to expansion as the transformer is used and heating
If it’s breathing your in trouble…

 

[PeterJ007]

More than likely a pocket of gas in the top and when the transformer heats and expands the gas goes somewhere.
Now that you’ve let enough of the excess air (gas, whatever) out there should be a partial vacuum on the transformer.
The little bit your getting now is still due to expansion as the transformer is used and heating
If it’s breathing your in trouble…

Thanks for your help/support Hv&Lv