Oil Filled Transformer with Nitrogen Filled. Vaccum is Creating Inside, Why?

No leakage??? Sounds like leakage to me.

(However, I don't know if the transformer oil can absorb nitrogen. If so, you might need to keep adding nitrogen until this process is complete, plus a bit more to develop positive pressure.)

Nitrogen may be required to prevent oxidation of oil. Pressure showing zero is not vacuum. Simply it means filled nitrogen is leaked. To withstand, plug all possible leak points. Up to how much pressure you are filling nitrogen? After filling check leak with soap solution. Monitor pressure gauge at regular intervals. If pressure reduces near to zero refill it, its so simple.

Dear Pritam,

we have checked all possiblities of leak but we didn't find anywhere. I am telling vaccum is creating because if I open OIL TESTING VALVE then it is sucking air inside. (it suppose to through oil outside). Actually transformer is fully filled with oil. We r unable to understand why vaccum is creating and to fill that vaccum if we supply nitrogen then after 1 or 2 days again vaccum is creating and there will be no nitrogen inside, we cant feel nytrogen everyday right? so pls tel me what should be done to solve this problem.

I hope its clear for u now.

Oil is kept under nitrogen atmosphere to to prevent oxygen and moisture to come in contact with oil. It can happen if it is breathing air in vacuum. Vacuum may be created due to temp drop, if nitrogen is not filled with positive pressure. A little vacuum may not allow enough breathing to deteriorate oil quality. So no need for frequent filling.

I asked about up to what pressure you are filling nitrogen? It seams you are not maintaining positive pressure, so how leak is checked? How much is liquid head above the OIL TESTING VALVE?

Actually if we see from top volve then it looks like oil is fully filled (100%) (looks like no head space, but then too nitrogen is filling inside transformer tank). We are maintaining Nitrogen pressure of 4 psi. By putting soap water in every bolt we checked leakage also. we didn't find anywhere. There is no Breather fixed to the transformer. It is fully air tight and outdoor type. temparature variation is also not too much. if we fill nitrogen in afternoon time (42 degree temp.) and check next day afternoon then also meter is showing 0, and if we open OIL TEST VALVE then it wil suck air inside.(when we fill nitrogen it will through oil outside, next day same time it will suck air inside.)

pls provide solution so that we can remove some oil and put nitrogen there to protect oil and winding from moisture and rain.

Is there a pressure relief valve? Is there any chance pressure is building up in the 42 degree (I presume C) temperature in the afternoon after you fill the tank with nitrogen, then relieving through the relief valve, and then the relief valve reseating? Overnight, the temperature presumably drops, creating a vacuum because the relief valve is reseated?

Just a wild-ass thought--I have no idea whether oil filled transformers are fitted with a relief valve--it seems like they should be, but perhaps set fairly high.

Am I missing something here?

OK a transformer may be delivered dry and nitrogen filled to save on transportation weight. Now why disturb things before the unit is due to be commissioned to part fill it with oil?

My 2^nd thought is why not fill to 100% and fit the silica gel breather? If needs be fit a temporary oil heater and pump to circulate the oil.

You are certain that nitrogen is not leaking from your tank because you don't see bubbles when you use the soap water test. The soap test is only good to a certain leak rate. If you have many leaks, each smaller than the sensitivity of the soap test, you will lose a lot of nitrogen. Temperature change will also affect the residual gas pressure. A source of pressurized nitrogen would be a good way to solve your problem.

You need an expansion tank of bag to compensate for expansion or contrction due to temperature changes from the temp at the ambient conditions of initial fill.

When Transformers are shipped from the factory, usually they have a vacuum.

This may be due to rail shipping requirements. I am not sure. Check with transformer mfg.

You need to have Engineer specify in "boilerplate" to have vendor install N2 blanket.

Either way, the vendor or the customer will have to crack the seal and some influx of air will take place, (sounds like it already did since you probably cracked the oil sample port to sample oil and noticed the inrush of air). You probably could have noted that this was under negative pressure by looking at the psi gauge prior to cracking the sample valve. If you don't have a pressure indicator you can purchase them from this website:

http://www.heartlandsolutionsinc.com/products.html

You need to have a temperature gauge, a pressure gauge, a +5psi overpressure release valve, and we like to install a N2 valve fill port on top. Sometimes you need to double up at one port because there are not enough. The drain/sample valve is on the bottom.

Depending on the size of your transformer you can use a conservator w/bladder or pressurized N2 tanks usually around 1800 psi with regulator to 3 psi and alarms.

Most small platform mounted oil filled have n2 blanket and pressure varies per mfg specs. Usual ranges can be from -5 psi to +5psi but I have seen -7 to +7. Some come with Ester Oil or Mineral Oil. Make sure you get the MSDS on the oil and type and keep it with a docmented manual on your xfmr.

Take an initial oil sample and have the works done on it. Including DGA, metal, furan, everything. This will be your baseline. Then put it on a PM and have it done annually or whatever your planner decides.

On our commissioning, we like to TTR, and insulation test for one minute Megger only on oil filled since oil effects megger testing as per their insulation instruction manual. You can do a DOBLE M4100 Power factor or OMICRON Power Factor test with the test set or a Capacitance and Dissipation Power Factor Megger test with their Bridge test set using the manual dial method. Make sure you have a good ground and follow your grounding safety rules. You can do a resistance winding test. Big transformers get the SFRA test before shipping and after arrival. Check your CT's and their wiring on the big ones. We commission our CT's also. Vanguard makes a good CT tester, but OMICRON just came out with a fancy CT test. See Utility Products April 2011 p20. We just purchased a new Vanguard unit so we lost out on this new method.

Good Luck with your xfmr. Have to go.

12 comments . . . and 12 DUDs.

I wonder why all of you - who seem to know nothing about oil filled power transformers - reply to the problem? I would be ashamed . . . .

The vacuum is lost due to DEGASSING of the oil - as the oil is typically full of nitrogen and other gases, . . . and in itself will evaporate and fill the vacuum space . . .

Much of what you say is correct, except that outgassing from a sealed fluid will increase, not decrease ambient gas pressure.

Exactly . . . the pressure goes UP from vacuum (-1 atmosphere) to 0 . . .
What ambient are you referring to? The discussion is regarding a sealed tank and the pressure within.

And the problem is that a vacuum is being created. Maybe the oil is sucking up the nitrogen? ;-)

Read the OP, and maybe other posts by the OP. They pressurize with nitrogen, the next day there is a vacuum. You seem to be describing just the opposite.

Sir, I agree that oil will expand and compress itself as per temp. but the problem is evening time when oil volume wil reduce in tank, then there vaccum will create inside tank and OUR WORRY is that time if it is sucking outside moisture from atmosphere then oil quality will reduce.

As per our observation there is no leakage, (otherwise how vaccum will create inside? if there is leak then outside air may fill inside vaccum right? but it is not happening, vaccum is creating) but another view is why nitrogen is not withstanding inside tank?

when there will be vaccum that time we are putting pressurised nitrogen inside tank 4 psi (sometimes 5 psi) but next day again there will be vaccum inside. (Is that nitrogen getting desolved in transformer oil?) pls reply me so that we can maintain nitrogen positive pressure inside tank. Depends apon reduced pressure of nitrogen correcting it weekly is ok, but everday is not possible right?) expect some solid answer from you.

Thanks in advance

Mahesh

Ok, now I (and I think you) understand what is happening. You fill the transformer with nitrogen in the day time, at night the oil contracts and creates a vacuum. (During the hottest part of the day, the relief valve might or might not be relieving.)

As someone else said, you need to contact the manufacturer.

You said the transformer is not commissioned yet--presumably you are also telling us that the transformer is not yet energized, either, right?

There is sort of a delicate balance at play here--you need to have the right level of oil, and fairly consistent temperatures, else you'll get the effects we're talking about when the oil shrinks at night. Once the transformer is energized, it will maintain a more consistent temperature, hence a more consistent volume, and the nitrogen will stay at a more consistent pressure--at least hopefully not get to above 5 psi where the relief valve will operate nor to a vacuum where moisture might be sucked in.

I think you should check on the manufacturers recommendations on how to store the transformer while it is unenergized, and follow those until you are ready to energize the transformer.

That might include draining the oil. Or, at the very least, testing it (again) to confirm it hasn't picked up too much moisture. (There are ways to dry the oil if need be.)

That delicate balance I talked about can also be disturbed if you've filled the transformer with too much oil. Then you'll have too little nitrogen to avoid getting to a vacuum when the oil shrinks at night.

Talk to the manufacturer. Tell him what is going on. Tell him the temperature difference between daytime and night. Tell him the transformer is currently not energized. Tell him the oil level (and at what temperature you're checking in).

Also, don't forget that the oil doesn't heat up or cool down immeditately. If you fill the headspace with nitrogen at the time when the outside temperature first reaches 42 degrees C and then seal it, the oil will continue to gain heat and increase the pressure in the nitrogen throughout the next several hours while the outside temperature remains at or near 42 degrees C.

You write:: >>expect some solid answers from you<<

Do remember that advice is as valuable as the $$ or Rupees you pay for it.

Now back to the NITROGEN, . . . the reason the pressure goes back to '0' after some time is because nitrogen is absorbed by the oil. This is especially true if the transformer was filled with good grade "de-gasified oil". This will happen again . . and again . . . until the nitrogen saturates the oil.

Note that when a manufacturer ships a transformer he drains the oil because of the weight, but all the windings and insulation remains 'wet' with oil. A bottle of nitrogen is attached to the tank via a pressure regulator, . . . with the pressure set to a fraction of an atmosphere (5 - 10 psi). The tank is not just filled to 5 - 10 psi, . . but maintained at that pressure for the duration - till it is refilled with oil again.

Some questions . . . does this transformer not have a reservoir tank? In which case it would be fully filled with oil - right to the top?

Reading some of the advice you have been receiving - I would run quickly to my insurance agent and insure anything you might do as a result of this advice.

Dear one and all,

Thank you very much for all your valuable comments.

Especially olehwi.

Thanks & Best Regards

Mahesh

Dear Olehwi,

can we have the solution to prevent creating vaccum inside the tank ? if there is N2 leak in minor way how to identify the same ? id there any other way apart from soap solution? which is identify by soap solution but N2 is getting dropped and created vaccum even temp is less than 30 deg C while Design temp is 50 Deg C.

just a thought maybe you overfilled or wrong type oil check manual

This transformer hasn't been comissioned.

DON'T DO ANYTHING WITHOUT THE MANUFACTURE'S PERMISSION.

It's very likely that if transformer fails, the manufacture will tell you that you did something wrong and the warrenty is void.

Before you do anything else, contact the transformer manufacture and see what he recommends.

CR4 is a great place to get ideas, but if you follow their ideas blindly, you won't have anything but grief.

What is the size of this transformer including weight with core? The typical small padmount transformer is shipped with the oil inside of it and it typically always has a vacuum on it. There is no N2 tank attached or anything like that. The mfg manual on these usually specifies a +/- range for the psi gauge. The level should be at the 1/2 way mark. As you sample, the oil level drops over time and eventually you need to add oil. I know of an incident in Canada where they kept sampling until the xfmr was close to empty. They caught it on an IR Scan. On these types of transformers, when they arrive after you unpack it, check it over for damage and loose or missing parts then you need to add N2 to get it into the + range. If it drops below the 0 psi range as long as it stays within the mfg spec it is okay and don't worry about it.

Temperature does affect this range so consult the mfg. If you live in a humid environment a + psi is preferred because the longer it stays in the - psi the greater the chance of moisture getting into the xfmr.

There are all sorts of physics involved with N2 and oil and pressure. Many of the feedbacks give great advice when they say "follow the mfg recommendation". As they say in the NAVY for those who know "RTFM".

Generally the engineers are on site during the purchase process at the mfg plant and observe the xfmrs being tested there if it is a large expensive one. The smaller ones may or may not be observed. The important part for commissioning is to get an initial Oil sample and DGA after ensuring the electrical is good so you can compare this future oil sampling tests. Also the oil sampling will catch any problems early.

You can purchase nice sampling kits from this website.

http://www.tjh2b.com/

If this is a large type transformer 55MVA with LTC and 7,000 plus gallons of oil or similar GSU type it is shipped w/o oil under vacuum and needs all sorts of attention during the commissioning process. The mfg usually assists you in this process because it is a very expensive piece of capital equipment. This involves placing the tank under vacuum and then adding oil via a HORI or other filtering process to ensure good oil. Your oil needs to be tested for dielectric strength prior to putting it into the xfmr using a dielectric tester with the round and not the flat electrodes. The round electrodes are the new standard. If you don't have a DOBLE account, get one. Ask these types of questions on the DOBLE forum and speak with your DOBLE field engineer representative that is local to your area.

What type of preservation system

Seal or conservator type