Transformer Oil Leak Mitigation

There are thousands, maybe even millions of small distribution transformers in operation around the world, and at least from what I see in my experience here in the US, it is not very common to find oil leaks at the bushing gaskets on large numbers of transformers unless they are all very old. Yes, the gasket material can deteriorate over time ("wear and tear"?), mostly due to thermal and ultraviolet degradation. However, if you are experiencing this very commonly, then your transformer supplier is cheating you by using inferior gasket materials. The nitrile rubber gasket materials used these days in good quality transformers is very stable and long-lasting. You either need to have a serious talk with your supplier, or find an alternate supplier who is willing to sell you better quality products.

As for repairs, there is nothing better than replacing the gaskets with new, good-quality nitrile gaskets (except replacing the transformer completely), but it is costly and labor-intensive. The repair putties are only temporary fixes, as they do not take the place of the gaskets, but only try to cover up the leaks. Their success is very dependent on surface preparation and care in installation, and even then the results are usually only temporary. They are only useful as a stop-gap solution when you can't do the job correctly right away.

The leak around seals where bushing comes out of distribution transformer may not be due to wear and tear.

These gaskets are synthetic rubberised cork and location is near top of transformer - that means not subjected to high static head of oil column.

Most probable reason of oil leak can be stress on bushing (bending force) caused by the termination of outgoing cables or overhead line.

As a first step, take shutdown, clean leaked oil around bushing, disconnect outgoing cables and see if the leak has reduced (if not stopped).

If stress on bushing is due to termination is the cause, then this is the culprit. Tighten mounting bolts of bushing and where connection comes out of bushing.

If leak seals, support the outgoing cables with additional clamp to reduce unsupported length, as close as possible to connection.

In 1981-85 I was in Middle East with an Electrical Contractor and experienced number of oil leaks on Distribution Transformers 750kVA to 2000kVA (but never from bushings). Since it was mostly at bottom (due to accidental puncture or weld failure in transportation/ handling). I had blocked oil leaks, and some time transformer energized in service, my repair kit used to be

1. Soap cake,

2. Quick setting epoxy (1 min or 5 min)

3. Normal Epoxy (hardens in 2 hours, full curing 24hours)

4. Fibre gloss tape 50mm wide or piece of fibre glass mat.

Technique used to be:

- Clean with solvent such as thinner CTC etc.

-Apply by pushing into leaks soap (it does not dissolve in oil. Only problem is that if leak is heavy or joint not thoroughly clean, it won't adhere to surface and slip off).

-If soap is held and leak arrested - immediately smear with thin coat of Quick Curing Epoxy. Cover maximum possible area beyond soap to form an umbrella of epoxy layer.

-You may find that oil is collecting in layer between epoxy and soap. Do not get panicked. Apply multiple layers of Quick curing epoxy, gently without damaging first layer.

- Next apply multiple layers of Fibre Glass cloth pieces soaked with Normal Epoxy.

- Spray paint next day over repair using small disposable spray paint can.

I remember in one case the leak was heavy from bottom most edge of flat type cooler fin and above technique was not holding. Following method was adopted.

- Made a tool to pinch approximately 50mm x 50mm x hypotenuse (Triangle shape) area of fin at the leak. From free flow the leak slowed down to seepage.

- Made Heat sink of 12 mm thick Cu plates approximately 150mm x 150mm.

- Clamped the heat sinks on both sides of cooler with 2 number of C Clamps.

- Cleaned the area of leak with CTC and asked welder to weld at small leaky edge (which was crack in original weld).

The leak stopped.

Non of above methods are written anywhere in Maintenance books and have been devised based on problem.

I thank God for giving me opportunity to start my career in Thermal Power Station of Tata Electric Cos. in 1972 to 81. That was the time that it was not easy to import spares or replacement items for Post War constructed Power Plant. As a result I used to think and design methods to keep plant always running. Plant availability in our time used to be the best in India.

Hope above is of useful

Ramesh