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Transformer oil leaks, How to repair it ?
5

Transformer oil leaks, How to repair it ?

Transformer oil leaks, How to repair it ?

(OP)
Guys,
I have 6 transformers each about 60 MW leaking. all transformer below 5 years old. and all leaks from flanges gasket. I already contact the XFMR manufacturer and no good answer.
I read on some papers that to fix leaks thats not big just use coumpound like glue around the gaskets,
Can anyone advise me with brand, manufacturer or web adresses, adhesives that works on fixing oil leaks ?

thanks
Pitat

RE: Transformer oil leaks, How to repair it ?

We have successfully used a product called Devcon.

RE: Transformer oil leaks, How to repair it ?

What flanges are you referring to, bushing?  If bushing, I would look at was it installed properly in the field.  Have you tried tightening the flange bolts to the proper torque spec?  Is the gasket material correct for the application, ie is there heating going on that exceeds the temperature rating?

For a txf leak repair kit, use a product by ITW/Devcon.  They make a complete kit called a Leak Repair Kit, Stock #DE120.  ITW Devcon is in Danvers, MA and the Technical Service phone number is 1-800-933-8266.

wbd

RE: Transformer oil leaks, How to repair it ?

Not so fast.  I think 'Yamin" wants to repair the leaky
gaskets by putting an oil additive into the oil, w/o
shutting down or draining the transformer (i.e.--a quick fix).

I checked on Devcon, and it is an adhesive to place on the
transformer gaskets, assuming the transformer is out of service and drained.  I would never compromise the integrety of the winding insulation with an 'oil additive'.

For all practical purposes, you'll have to take the
transformer out of service, and have it sent to a repair
facility to have new gaskets put on.

Our specifications are pretty stringent, and we can usually
award a bid contract to only the best manufacturers.

In U.S., the best (manufacturer) is Waukesha Electric Systems (Five year warranty).

Five years is pathetic.  Normally, we expect new substation
transformers to go for 20-30 years w/o major fixes.

RE: Transformer oil leaks, How to repair it ?

In our use of Devcon we applied it with transformer in service. The leak was at the bottom of the cooler, where tubes penetrate the tube sheet. We put the liquid gook into the accessible areas from the back (suction) side of the cooler and it flowed around the tubes and then hardened later. A flange would be more challenging geometry to hold the gook in place while it sets... but I have heard it can be done.  The product is thick enough that I don't think very much can possibly get through small leak holes into the transformer oil (although I agree it's a calculated risk).

RE: Transformer oil leaks, How to repair it ?

(OP)
Guys,
We like to repair without drain the XFMR but we can afford to shutdown the XFMR.
Another question, if I drain the transformer should I purify the oil before I put back into the XFMR ? (the risk of moisture content above the permitted level)

RE: Transformer oil leaks, How to repair it ?

If you are going to shutdown the transformer, then
you should go ahead a replace the gaskets, especially if the cooling fins are leaking.

The external patch 'dope' is less desireable than replacing the gaskets.

When we replace or add oil to our transformers, we always
filter the oil first.

The oil should really be drained in a factory setting, and
ideally, it should be done under very dry conditions, to
reduce moisture absorption by the cellulose insulation.

I heard a report where a utility received a new transformer from Virginia Transformer, in which the semi driver reported that the factory had to drain the oil from
the tank, in order to make the unit light enough to lift
onto the semi bed, then re-filled with oil.  The utility
rejected the transformer when they heard this, for the reason the insulation may have been compromised during the time there was no oil in the tank.

If you can, try to keep the tank filled with oil, and
close the isolation valves on the cooling fins before remove the fins.

Can you tell me the manufacturer of your crappy transformer?  I would like to report this to another
utility, so as we can avoid buying their product.

I have traveled to the factories several times to witness impulse tests, and perform my own mini QC check, before
OKing the unit for shipping.  The manufacturers can be pretty sloppy anymore.  You would be amazed at the crap I see.

RE: Transformer oil leaks, How to repair it ?

We had a leak on an inlet fin of one of our 24mW station xfmrs 5 years ago.  A service company called United Power Group(UPG) located in Brockton MA, actually pulled a vacuum on the xfmr and repaired the leak, filtered the oil, and performed a disolved gas analysis.  This was all done in the field with the xfmr taken out of service.

RE: Transformer oil leaks, How to repair it ?

(OP)
I agree to Sphincterboy Change the gasket is more preferable, but Guys I live/work for A Power Plant In a very remote island  in a third world, near the equator line and ambient temperature is about 33 to 36 degree celcius.(to have internet line here is a miracle).
Without load My Xfmr on midday sunshine the temperature reach 55 degree C.
To get a Purifier company on site would be very expensive, compare to try first with "patch dope".
If Patch dope donot work, I have to change the gaskets,Now My XFMR have "Granulated cork bonded with medium nitrile butadiene rubber" gaskets. I believe this kind of gasket is for flat of flat surface, and if i want to change the gasket to more temperature proof like Viton is that acceptable ?
Does anyone have experience with XFMR with Viton Gasket ?
wbd, I cant find stock # DE120 on Devcon web site,
Sphincterboy I can tell you the manucfaqcturer name here, but When I try to get their service engineer on site to see and resolve the problem, I said will pay for the engineer and ask them to name the price, they said no, we donot want to come to site. I like the word crappy.

RE: Transformer oil leaks, How to repair it ?

SMLD - pulled a vacuum on the transfomrer and opened an [unisolable?] flange without taking it out of service?  I have heard stories about putting just enough vacuum over the oil to prevent oil from coming out when the flange is opened up.  Is that what they did?

(it sounds totally whacko to me.... if the bubbles coming out of solution don't get you the bubbles coming from the open flange will)

RE: Transformer oil leaks, How to repair it ?

Yamin, it looks like you're stuck.  

As I see it:

   1.  You cannot get service from the manufacturer.
   2.  You cannot drain the transformer (too humid/hot).
   3.  You cannot afford to hire repair services.

You most likely have to apply the external sealant.

You should call the Devcon telephone number, if the stock number is not listed on the Devcon website.  At any rate,  get the stuff!  You may have to repeatedly apply the dope, to keep everything kosher.

If you insist/want to change gaskets w/o draining the tank,
then focus on the radiator gaskets, and top primary/secondary gaskets.  Make certain no rain water (a tent?) comes in through the top bushing holes.  The bushings should have draw leads.

You should (gasp) plan on purchasing a replacement unit
right away, since leaky gaskets might not be the only part/item wrong with the transformer.  If you need specifications, I can e-mail you some fairly decent specs., which will get you, in all probability, a Waukesha Electric System transformer.  Also, you should reserve a factory visit, to witness testing.  A thought: you
might contact Waukesha Electric Systems at 1-800-835-2732
to discuss your issue with them, to see if they may be able to help.

I am very sorry for your situation.  I wish ANSI would
raise their standards to cover such issues as warranties and service, and manufacturing standards.  As I see it, ANSI is bare minimum, to allow even the worst manufacturers
to squeak by.

RE: Transformer oil leaks, How to repair it ?

Yamin,
I called Devcon and they still make that repair kit, stock #DE120.  They said they do not have all their products on the website.  Use the website to find a distributor near you.

I have drained txf's down to make repairs and then had a oil processor onsite to hot oil clean, draw vacuum, dry out transformer and re-fill with no adverse affects.

I have used Viton to replace cork/Buna N gaskets.  You need to find the right grade of Viton for your temperatures.  I would change your txf spec to make sure the manufacturer uses Viton gaskets for high temp areas or if it is a silicone filled txf.

good luck
wbd

RE: Transformer oil leaks, How to repair it ?

WBD,

Thanks for the info. on Viton.  I am changing my
transformer specifications for Viton gaskets right
away.

Thanks!

RE: Transformer oil leaks, How to repair it ?

(OP)
WBD and Sphincterboy thanks for your helpful post,
I'm going to buy Devcon product.
If both of you have spec or table of gaskets including viton please send the information to me ledig18@yahoo.com.

again thanks for your helpful post.

Regards
Yamin

RE: Transformer oil leaks, How to repair it ?

Transformer leaks are a mess itself!
Let us look at the Devcon product.These are basically quick setting epoxy compounds which fills the gasket space or the crevices in gasket so that oil sealing is achieved.But its efficacy is limited and  is only a temporary solution.Most important in its application is that oil leak has to be stopped temporarily during the glue application.If the leak is not profuse,you can achieve this by  creating  a vacuum over the conservator top (check whether the conservator can with stand vacuum!) Otherwise you have to drain oil. Then there is the option of gasket replacement .Then wipe off oil from leaking points ,clean the area and apply the sealant as per the combination recommended by the manufacturer.Release vacuum after the setting time furnished by the maker.
In transformers different types of gaskets are used.All are quiet effective ,provided material of proper specifications is used and flange surfaces are properly designed and suitable limitators or grooves are provided to avoid overcompression and setting of gasket/oil seal.Agood designer will normally take care of all these and leak proof trfs can be easily achieved.

1) Gaskets. These are of rectangular section 1/4 or 3/8 inch thickness and of width 10-25 mm effective width(width helping the leak)Most commonly used gasket is of cork -rubber
(made of nitrile rubber and cork granules 50:50 ratio)Compression is to be limited to 30-40% by  metal limiters or grooves in the flange.This is quite adequate to a temp of 90-100 degree centigrade.Where higher temp is expected (bottom of high current bushings)synthetic rubber gaskets -silicon rubber or viton is preferred.Viton is also used where ambient temp is below minus 20 degree centigrade or when silicon oil is  used.
When rubber gaskets are used ,instead of rectangular section,circular (O-rings) or chords are also used.

Find out which type is used in the leaky trf and evolve replacement strategy.One easy way is to  use 10mm thick 15 mm wide viton gaskets,even though costly.In Indian subcontinent viton costs nearly 7 times more  than nitrile rubber. Dont forget to apply  rubber sealing paste over the gasket surface.
There is absolutely no need for specifying viton sealings for trfs as cork -rubber or nitrile rubber gaskets are quite effective for the purpose and proved their worth for the last several decades.

RE: Transformer oil leaks, How to repair it ?

Once again a mention of drawing vacuum on top of oil (prc).

I was always taught this was strictly forbidden. The danger would be that gases start to come out of solution during the vacuum. If you don't drain and refill under vacuum, it's tough to assure yourself there are no residual bubbles within the windings.

It may be an overblown fear, but it was the stict practice of a large utility that I used to work for.

RE: Transformer oil leaks, How to repair it ?

(OP)
Guys,
 Before prc post I got the impression from Electricpete post that devcon can be applied on oily surface or not stopping the leak or drain the transformer.

RE: Transformer oil leaks, How to repair it ?

elecricpete's learning was correct-normally vaccum pulling over oil  level  in a trf should be avoided,for fear of gas bubble sticking in to windings.But when there is a leak rectification (eg welding leak)this is the only solution known to me.But we must give a settling time of atleast 24 hours before energising the trf so as to get the bubbles dissolved in to oil.
There are products that claim application in the oily condition itself-but I have no experience and also compatibility with trf oil is to be checked.If some body can try,well and good.One such claim-www.durmetal.com
Durmetal AG ,Switzerland

RE: Transformer oil leaks, How to repair it ?

(OP)
Anyone have experience with Durmetal ?

RE: Transformer oil leaks, How to repair it ?

A note of caution on welding to repair a leak - make sure to have a inert gas (nitrogen) in the gas space.  I would have a bottle connected to maintain the gas and also probably do a couple of gas space purges with N2 prior to welding to ensure any explosive gases have been removed.

RE: Transformer oil leaks, How to repair it ?

2
A lot of good hints.

I have repaired many of these.

Here is what I would do if it were my unit.....

Drain the oil, while you fill the Tx with DRY (-55C) air if available. (Maintain positive air pressure)  Replace all the gaskets with mild positive air flowing thru windings (still use -55C air!!!)  When you want to refill, get a small vacuum pump.  The tx can be vacuum filled with a small unit if the correct instrumentation is used. Prior to fill, pull vacuum of 1000 microns or less for 24hr, prefereably during a warm time of year.(obtaining the vacuum with a small pump may take two days).   So long as positive pressure from the oil pump is maintained during filling, and the pressure in the tank does not exceed 500 to 1000 microns (ask your Tx rep, if they can even answer, if not, go with 1000microns)   the unit may be filled.  You must take care that the dew point inside the unit is -30 or lower and that the leak rate is less than say 100 or 150 microns/hr before you fill.  

  

Boil off and leak determination and dew point are possible with the use of remote tank mounted probes.  I know of several products that may temporarily fix the leak but they sure make a mess when you go to fix it for real, and you will fix it eventually, that is certain.

Bruce

RE: Transformer oil leaks, How to repair it ?

What bru suggested is the ideal way of doing it .But in many remote sites in third world it is next to impossible to get all this.Can you suggest some details of remote tank mounted probes for leak detection and dew point meaurement. Model no, make,address or web site?
 wbd is suggesting repair of weld leak.Trust he is suggesting to drain oil before welding.I always recommended this rectification in oil filled condition based on some old Westinghouse recommendations,ofcourse with vacuum over the conservator.

RE: Transformer oil leaks, How to repair it ?

prc
Hastings makes some good vacuum probes, or a simple monometer will do. (this is often the best anyway).  You can view their stuff at http://www.hastings-inst.com/

For dew point, Panametrics in Ireland are well trusted in utility circles.  View their stuff at http://www.panametrics.com/

It may be of value to measure the dew point and temperature of the oil at the same time.

The temperature of the transformer is critical in determining boil off and moisture content.  Temperature measurements are best done with a precision milli-ohm bridge on the winding with the appropriate calculations, to give true winding temperature.  

The more I think about it, the gaskets are likely of poor quality and have simply compressed.  If they have gasket stops, there may be no point in tightening, but if not, the gaskets may have room to compress some more.  For poor quality cork neoprene 5 years is about the perfect time for retightening gaskets.  This cannot be done with torque specifically, it requires the touch of an experienced transformer man.  Torquing will only squish the gasket around and the originator of the torque spec cannot know the density of the gasket that may be in use here.

RE: Transformer oil leaks, How to repair it ?

Sorry, just a bit more...

These items are not specifically hard to get in north america and you will simply have to add the logistics of getting to the remote areas to thier deliviery.  Most of these units are in the posession of utility people and can often be borrowed.  I have had good response from suppliers in Canada, in as little as overnight for many products.  If you can source 1 clean tanker, one small vacuum pump and 1 small oil pump (300 gal/hr) that should be all you need.  Mini oil plants are also not uncommon and will provide both a filter press and vacuum processing with only 600V 3 phase power.  The plants will ship on a skid and weigh <2000lbs.  Visit http://www.baronusa.com/ for some examples of these.


The precision bridge may be substituted with a DC current source of approximately 10 amps, a good ammeter and a volt meter.  The calculation will show the correct resistance value.

I can post some moisture determination curves and other procedures related to this if you need.

Good luck, Yamin, and email me if you need more info.  

RE: Transformer oil leaks, How to repair it ?

bru,thank you for the information.I believe dew point and temp are not of oil but of air inside tank.If your curves are different from the ANSI curve pl post the same.Dew point meter is the cloud chamber type or different?

RE: Transformer oil leaks, How to repair it ?

prc..
Dew point can be taken in oil.  The probe is designed for it and moisture is derrived from temp and dew point.  

I am not familiar with the cloud chamber type.  It is simply a probe with matched transducer unit (they are sold together as one unit) and require care in handling but are simple to use.


The air probe and oil probe are each designed for thier specific purpose but the operation is the same.

Oil probes are usually flushed with process oil on partial bypass during process or filling.

I use some GE info and if they are different (I never really compared the two) I will post.
Bru

RE: Transformer oil leaks, How to repair it ?

bru,
I think we have some communication gap!
In your posting of 27 th Jan you have said of dew point measurement of dry air and limit is-30 c . ANSI C 57.93 also recommends on these lines.Now you are talking of dew point of oil. Why we should check that?
What is meant by boil off?
I have heard GE pioneered these checks to ensure dryness of the paper insulation in trf and also to avoid condensation from out side air.

RE: Transformer oil leaks, How to repair it ?

prc
The dew point of the oil would be valuable only to check that the oil being pushed into the unit is still dry after being in storage outside the transformer tank.  If the oil shows a moisture content higher than 10-12 ppm higher than what came out of the Tx tank originally, you could have problems extracting that moisture as it enters the tank without heat.  (We dont have heat if we are not using a processor to put the oil in the tank.

The -30C is the max temp (looking for dew point <-30 if possible) is what we would want to see in the tank prior to filling.  This is with the vacuum on after 24 hrs.  (Usually 12 is sufficient but this area may be more humid).  This may be unattainable if the winding was exposed to humid air for too long without positive pressure from dry air.  Theoretically, the longer the winding is exposed to vacuum, the dryer it should get.

It is possible to use nitrogen but the removal of secondary bushings almost allways requires working inside the tank.

Air dryer units can be used.  They are made by many suppliers worldwide.

Boil off is also referred to as blank off, and is a measure of how quickly the pressure in the tx tank comes to equilibrium.  That is to say, how much moisture comes off the winding insulation before the vacuum in the tank is no longer sufficient to vaporize more water.  The tank is blanked off and the pressure in the vessel observed over time.  The pressure change vs. time will be non linear for the first few minutes.  After that, the linear change in pressure relates to leak rate.

Given temperature and pressure, a moisture content can be calculated.  (The Boyles law thing)

Most of the docs I have are from utilties adopted methods but those, as I understand, are from GE, and a bit from Westinghouse.

Just a question for Yamin, if you are still watching, what is the kV of these units, and the BIL?

If they are <=60kV I wouldnt bother with vacuum filling at all but for the fact that the climate is sooo humid.

Also, we must take care that these are suitable for vacuum fill and they were not assembled in a "vapor phase".

Bruce

RE: Transformer oil leaks, How to repair it ?

(OP)
Bruce,
Its a 11kV/150kV Xfmr and the BIL for HV line 650 kV,HV neutral 95 kV, LV line 110 kV.

Guys I already try to glue the leaky flange for 2 days, about 36 hours shut down the Xfmr,During that 36 hrs I try different ways on how to glue it and still leaky.
 I use biofix 911 and biodur 561 and it just slow the leak down not fix it, maybe I need to use another glue.

I decide to bring the company/contractor that have xfmr oil purifier on site and change the gasket and top up the oil.

I really want to have viton gasket on my flange, please advise me with company that sell sheets of viton,

Thanks
Pitat

RE: Transformer oil leaks, How to repair it ?

I seem to have a similar problem to yamin.  We have a 2MVA oil-filled transformer that has a seam weld leak in the main oil filled steel box part, right underneath where we can only get at it by hoisting up the transformer on a crane.
We are in the Sahara desert and back-to-manufacturer repairs are difficult to say the least.  It came from France, along with three others which survived the journey. We have had the weld repaired offsite twice but the metal is thin and the weld seems to open again whenever they re-fill with oil and send the transformer back to us ( 120 miles of bad roads to the local electrical repairer)
Would be pleased to hear from y'all about possible application of external "cold weld" or epoxy product in-situ with transformer full of oil as no-one on site wants to risk taking the oil out due to potential contamination.
Photos available. Thanks.

RE: Transformer oil leaks, How to repair it ?

You might consider fastening a conformal plate using the Devcon product.  The quanitiy of adhesive needed will probably be much larger, but likely cheaper than a shutdown and oil pumping.

RE: Transformer oil leaks, How to repair it ?

Mr. Geoffreydavies

For "coldweld" work I suggest you use Durmetal products. It's far better than any epoxy product in the market. Its easy to use and it works. It even works on oily, greasy and wet surface. Unlike anyother products I've used before.

RE: Transformer oil leaks, How to repair it ?

(OP)
Guys,

Probably its little bit late but I think I need to post the result of my repair to leaky xfmr.

Here's what I did,

1. I get permission to spend some money to bring a contractor that specialize on xfmr oil filling with their purifier. We change the gasket on 2 xfmr that the operation give us to have 5 days outage on each xfmr. Change gasket spec from cork nitrile to buna nitrile. it take 12 hor to drain the oil, push by nitrogen, open the leaky flanges let the nitrogen to flow to the air make the pressure of the tank higher by nitrogen (by doing that I use 10 bottle of nitrogen on each xfmr), and change the gasket.
Start to fill the xfmr and purify the oil for 72 hours and let the xmfr sit for 24 hrs and reenergized, result OK, Done that April 2002, so its been a year now and no new leaks.

2. On the other 4 xfmr I only have permission only 1 day shut down, so decide to patch, gave contract to 2 different glue vendor, one Prolong  and the other one Belzona, both of them got their technician come to site to apply the glue.
Both almost have the same procedure of applying the glue. Done that in May/June 2002. No laks untill now.

Hope my experince can help some one out there with similar problem.

regards
Pitat

RE: Transformer oil leaks, How to repair it ?

Thanks for the update.

RE: Transformer oil leaks, How to repair it ?

I think your transfromers are manufacuterd by BHEL. If yes nothing to worry because there is no transformer from BHEL without oil leak.
You can Devcon 5 minutes putty and class A putty for arresting oil leaks. But putty is not a solution for many leaks like valve joints, OLCT joints and tank rim joints.


RE: Transformer oil leaks, How to repair it ?

I tried the Devcon DurAlloy on a transformer.  It worked well at first but did not last very long.  After a few weeks the repair cracked on the transformer and oil leaked again.  I also did not like that it took an hour to cure.  The worked at first and then fell off after a few weeks.  The stuff from Velodur Durametal never stayed on.  I could not get it to adhere to the oily surface like it said it would.  I had to apply adhesive onto a piece of Kevlar and then stick it to the transformer.  It was messy and I had a problem applying it before it cured.  I did find a product from American Polywater called Power Patch that worked great.  It was easy to apply and has been on the transformer almost a year without failing.

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