oil leak in transformer

Well, the first thing that comes to mind is not to stick a sharp object through the case.

Secondly, I reccomend that your superiors keep you and all sharp objects from the proximity of the transformer.

Some transformer manufactures:

Before the transformer is filled with oil,

Apply 5 pound/square inch air pressure to tank.

The air valve is closed and the air pressure source is removed.

The transformer is let overnight.

If the pressure inside the transformer tank drops, there is a leak. The leak is repaired and the test is repeated.

Repairing leaks after oil has been placed in tank is much more difficult. The transformer manufacture should probably be consulted. Some people say you can apply a vacuum to tank and weld the leak. Some people say this won't work.

Some people say to apply vacuum to tank, apply solvent to leak to remove oil. Apply Locktite to leak (Tank still under vacuum), then apply heat to set the Locktite.

Dear carl

Thank you sir.

And how the bolt and nut and flange etc are selected to avoid leak

i.e.,which type of material we have to select for bolt and nut

then torque for tightness etc

please share your views

regards

gova

With a straw dear Gova dear gova,dear Gova With a straw dear Gova, dear Gova with a straw... A dhildren's song for a children's question.

The bolts and nuts are usually the cheapest galvanized steel bolts that the hardware store has.

The bolt diameter is usually twice to four times the flange thickness.

Bolts are usually tightened so the sheet gasket is compressed 10% to 40%.

Sealing is only a minor part of tank design. Wall thickness is probably the major part of tank design/cost. Gasket material and installation are also a major part of the design.

If you would explain why you are interested in "oil leak in transformer", we might be able to provide more specific details.

DO NOT USE GALVANIZED BOLTS, NUTS OR VALVE PLUGS on steel transformer. Can produce H2 if in contact with the oil.

Hi

Eventhough the question is like children's question,the answer from Mr.Carl and Mr.Simon is excellent and practical and it is very useful to me and many others.They share their experience.I wish to salute them.

In one of our site,oil is leaked through a bolt in the radiator(33/11KV 8MVA Transformer).There is a argument between my boss and the manufacturer that the quality and type of bolt is poor.

Hence I generally asked this question.(Actually the leak is through radiator)

Regards

gova

As a guest, it would appear that a very unproffesional sarcastic remark, to a very proffesional question shows where the actual skill lies and where the luck lies,eh?

Those posting proffessional repiles are a credit to the industry......keep it up fellas!!

There are two type of transformer in the market. One type of the transformer is with the conservator oil tank and the other type of transformer is with out the conservator oil tank. The ones without the oil conservator tank are call hermetically seal type of transformer.

Both types of the transformer have its own advantage and disadvantages but never the less, what is more importance, is the proper procedure to be carry out at the initial stage before filling up the transformer with the transformer oil.

All valve must be close during the transformer is under vacuum. Minimum time is about 36 hours or if the vacuum negative pressure has reached to the negative pressure required.

Then the vacuum pump will be shut off and maintain the negative pressure inside the transformer for another 24 hours to see if there is any leaks. If no leaks detected, transformer oil will be filled in, thru the bottom valve of the transformer by vacuuming from the top of the transformer. This process will be continues until the transformer oil had cover all the transformer winding.

This importance steps, is to help to remove out all the moisture from the transformer winding and also the air that trap inside the transformer winding. Once your transformer had set up according these procedures, then you will have a good transformer and the oil will never leak. This procedure will be applied to oil conservator tank type of transformer and the hermetically seal type of transformer

For hermetically seal type of transformer, one importance step is not to overload your transformer. Once your transformer is overloaded, the transformer winding temperature will increase and your transformer oil will expanded. Since the hermetically seal transformer is all seal up, the transformer oil had no place to go but start to leak from the transformer seal. As the transformer oil is heated up the viscosity of the oil will become very thin and it can slip out thru these seal. Most of the oil will leak from the seal from the top cover of the transformer.

Proper sizing of the transformer is importance as to prevent all these un-expecting problem to arise few years later after operating it.

For me, I always prefer transformer with conservator tank. It can help to solve all these oil leaking problem. If the transformer oil expanded, the oil can flow back to the conservator tank.

It's unlikely that the leak is caused by the bolt.

It's more likely that the O ring or gasket has been damaged, or the joint is damaged, or there could be a leaky weld or ???

DIFFERENT ENGINEERS, DIFFERENT VIEWPOINTS:

Hermetically sealed transformer is a transformer where the oil is not allowed to contact the outside air. It may be either with a conservator or with an air space above the oil or using bellows.

Transformers should NEVER be filled from the bottom using vacuum. If there is an air leak, the air goes throughout the transformer. There should be two fittings on the top of the transformer, one fitting should be for the vacuum and the other fitting should be for incoming oil. The oil should be splashed over the transformer, then if there is air or water in the oil, it will be removed.

This is the right way to fill a transformer under vacuum, make sure tank will withstand a true vacuum. I have actually seen a transformer cave in under vacuum. If a leak is detected after filling with oil and vacuum is released, place approx. three to four lbs. of vacuum and weld it up.

A slight correction:

This is more accurately defined as "Tank types" or "Oil Preservation Systems". There are three (3) main types with sub types.

Large Power Transformers are most commonly "Conservator" tank types. As the loading on the transformer changes the Liquid Insulation (Dielectric Fluid. Oil. Silicone, etc) expand or contracts. The main tank is totally filled with no head space. The Conservator tank is used as a reservior for the oil to expand into. Most have bladders to prevent exposing the fluid to atmosheric gases. Some "Free Breath via a dessicant". The Bladder type units thus have very low levels of dissolved gas Atm. gases.

The Next type is the Sealed Tank units WITH HEAD SPACE in the main tanks over the core and coils for expansion of the oil. These are sub-divided into: a) ACTIVE NITROGEN BLANKET systems having headspace pressure regulating systems using compressed gas cylinders of nitrogen. B) Sealed Nitrogen Blanket units. C) Sealed with Dry Air. The Nitrogen is critical in highly loaded units to reduce the Oxygen content to eliminate the oxidative degradation of the oil and the cellulose insulation.

Lastly (of the fluid filled transformer types) is the Free Breathing units. These often have a "breathing tube" with Dessicant material to remove water to prevent positive or negative pressure in the head space. These are smaller units. High interchange or venting of fault gases to the atmosphere.

Joe

Hi Gova,

In your case I think the leak is either due to the over/uneven tightening of the bolts and nuts that allow some leakage through the gasket.Is it newly installed ?If the leak is at the bottom of the cooling fins then it could be due to faulty welding,mechanical damages during installation or some rust spot at the welded points.

For 8 MVA power transformer,it is about 18 tonnes.The main tank can still be transported with factory filled oil.The radiator fins that are delivered seperately are installed onto the main tank at the site and fill with drums of oil handled by a small mobile filtration plant on site.Careful handling of parts,gaskets and torgue wrench are necessary.

On other topics mention by both Simon Wan and Carl Pugh about oil immersed ONAN cool distribution transformers,my opinion and some of my knowledge are as follows:-

1.As a user,consultant engineer or manufacturer I definitely prefer Hermatically sealed oil immersed transformers.From the capacity ranging from 50kva to 3MVA (5 tonnes) sealed type is possible,simpler in design,cheaper to make,lower in maintenance,more compact and lighter.Doing away with the conservator tank,therefore no need of silaca gel (needs changing or drying) breather,total height (reduces packing costs)and weldings,oil level indicator,extra oil and pipes are eliminated.The expansion and contraction of the volume of oil in the transformer between full load and low load periods are absorbed by the expansion of the corrugated fins ( bellow effect ).These fins side walls which are formed by 2 long strips of 1.5 to 2 mm thick mild steel sheets which are welded ( 2 lines )together vertically,makes the sides of the tank.The top and bottom plates are 5 to 6 mm thick mild steel plates.Top cover,I prefer welded and fully filled type instead of bolted type.In hermatically sealed type there is one with nitrogen gas fill top (about 5 to 10% of tank volume for oil expension and oxydation prevention) and fully filled type.The gas leaks after one or two years.Some British factories and those who use their designs are still making radiator fins with conservator type of distribution transformers.They do not get big contracts when the specs are modern,fair and reasonable.

2.In transformer factory,the assembled coils and core is dried in an oven for two days,heating and cooling.For a 2 MVA transformer about 5 to 6 litres of water is driven out of the transformer material.It is then tanked.Several transformers are pushed into a pressure vessel with oil pipes for partial vacuuming and follow with filling of oil while in the vessel.This process will prevent any formation of air bubbles or water condesation in the coil or core assembly which will cause partial discharges and insulation failure.However when you change old transformer oil at site,oil can be fill from the top via the oil level indicator's top cover or conservator tank cap or bottom drain valve ( flooding) and there is less problem of air bubbles formation because the uneven parts are already coated in oil.There are usually no openings make specially for the filling of oil .High vacuum should not be used.It will collapse the tank beyond repair.

Regards,

Khor.

Dear sir

Herewith I am attaching the photo containing the bolt in the radiator sub-header where the oil is leaked.

Regards

gova

You should locate where the oil leak is, and if it is a gasket, damaged fitting or weld.

Use a rag or paper towels and remove all the oil on the outside of the transformer. If necessary use solvent on the rag or towel.

Run your finger across where you believe the oil leak is. Check your finger for a film of oil. Repeat at different locations until location of oil leak is determined. If oil leak is small, you may have to wait and repeat the tests.

I was probably too specific in saying transformers should never be filled from the bottom. The correct answer is the transformer manufacture should be consulted on the procedure to fill the transformer.

Gova,

The picture shows some oil mark on the bottom part of the front surface of the plate stamped "CTR",this part is not a bolt or nut.This looks like the end cap of a hollow tube that all the 12 or 14 vertical fins are welded to.(point with a 15-cm pen & isometric view will be clearer).The frontal end cap surface is the unlikely place where leak starts.Please follow Mr.Carl Pugh's method to locate the exact spot where the leak originate.The leak looks small as I do not see drops of oil hanging at the under most area when the picture was taken.It looks like more than 5 minutes per drop ( I am guessing).The oil can travel horizontally due to surface tension.

First,find out if/confirm that,this problem on this transformer is not covered by the manufacturer's warranty and you have taken enough pictures and contacted the insurance people in case you can claim compensation from them before removing the evidence.

Have a look/check from the top,downwards ( on each fin,two surfaces ) to the place where you see oil mark starts.Also look at the cylindrical horizontal tube where "CTR" is welded to.Please look horizontally towards the main tank.If there is no traces of oil as you get closer to the tank,then the leak is on the outer few fins.In short narrow down the search area .Then you can use cotton rags or old T shirt to clean the complete oil stained area with car shampoo/dish washer liquid.At this stage do not use sharp metalic and abrasive tools such as metal brush.Pay special attension on the the curve welding lines between the tube and the fins and the bottom welding lines (use a mirror if it is too low ) of the fins.Look for any decoloration/rust spot,dents,deformation/crooked fins.Take pictures for records.When the clean part is dry,put some talc ( baby powder ) on the suspected area/spot and observe.If there is a leak,you can see that the colour of the surface changes with the shape of the tiny leak line or hole which is the exact spot of the problem.( when you put some oil on the "dosei" on the frying pan,that part of the dosei that has oil patch will turn from white to light brown ).

After you have located the source of leak,kindly give some picture ( macro range/close-up shot).I hope to help you to repair it remotely.Actually the manufacturer should be able to help you on all these for a small fee if any. By the way, how did you post the picture on this forum?

Regards,

Khor

hi folk....

now a days...some foam sprays are available in the market. which can easily solve ur leakage probs....

Oil leakage is not big thing in running plant...

santhosh

Dear Santosh,

I am eager to know about the srays which you have discuussed in your earlier post as i have never come across those sprays and i am worried about welding leaks...

Regards,

Naveen

Your Oil Leak is not severe but you are right to follow it up

MOST leaks are due to poorly installed gaskets (not the correct size, thickness or torque used). Next common source of leak is gaskets made of the wrong material (incompatiable) for the fluid type. This causes the gasket material to swell. Last in poor quality welds or joints between radiators and tank.

The comissioning (setting in place) of the transformer is critical. The company that installs a new or rebuilt unit must be very experinced to insure this critcal phase is done correctly.

By the way most problems with the quality of the oil in a transformer is created druing the on site commissoning of the transformer.

It can not stressed enough the the company and person who install you transformer is critical to the life of teh transformer and elimination of most leaks.

Hi,

leaks can be tested with NDT spray test (penetrant, developer and cleaner) before and after welding and Foam spray during air leak test. There is also a flourescent solution used for leakage test which can replace hydro test on small tanks. I dunno what is the actual defect in the picture, but it can be due to welding defect due to high stress at that junction (parts tolerance is also equally important for fit).

I also have a question to post, please kindly lend your expertise. Has anyone used or seen o-rings type groove for the mating surface between tank and cover? Is milling or machining required on the mating surface? I am also facing leakage there and we are able to identify it but I cant understand the root cause whether it is due to current process of hand grinding and polishing or gasket issues or bolts tightness or tank design issues. If you are doing machining, is it before welding or after welding the tank. what is the surface finish, Ra advised.

Cheers,

Waseem

Interesting thread. I had to respond to this.

The utility that work for has somewhat mastered the concept of leaks in transformers. Most of the time leaks will occur due to corrosion hence will get a pin hole. This should be part of basic maintenance and up keep to properly coat the fins and areas around the bolts and joints with a corrosion resistant epoxy coating. We have had great luck with this in keep the transformers in good shape for years. As soon as the coating peels off, we normally recoat the areas that you see rust development.

For exsisting transformer oil leaks dielectric fluid and SF6 as well as nitrogen issues on active leaks, we have used several on the market but we have the best luck with EMP Inc.'s Transformer Leak Repair Kit . You can find it on google searching "EMP Transformer Leak Repair Kit" or transformerleaks.com I believe is the site. The concept is simpler instead of using locktite and from experience more permanent. A 3 step process to seal an active transformer leak without draning. Hope this helps.

Eric Beeman
Nuclear Power.