By hvhipot 
Power transformers are mostly oil-immersed transformers. Over the years, oil leakage of high-voltage test transformers has occurred from time to time. Severe leakage not only reduces the service life of the transformer, affects the safe and stable operation of the system, but also benefits society and users. Cause serious impact. In recent years, during the overhaul of the main transformers and plant transformers of various power plants, we found that the reasons for transformer oil leakage are as follows:
1.1 Rubber seal failure and weld cracking
Transformers have many welding points and long welding seams, while oil-immersed transformers are a collection of various welding and connections based on steel plate welded shells.
A 31500kVA transformer has a total of more than 70 welding joints, and the total length of the welding seam is about 20m, so there may be many leakage channels. The cause of direct leakage is the failure of rubber seals, cracks in the welds, pores, slag inclusions, etc.
1.2 Aging, cracking and deformation of sealant
Transformer leakage mostly occurs at the connection, and more than 95% is mainly caused by the sealant. The quality of the sealant mainly depends on its oil resistance. If the oil resistance is poor, the aging rate is faster, especially at high temperatures, the aging rate is faster, and it is easy to cause the seal to age and crack. Deterioration, deformation, and even failure, causing oil leakage of the transformer.
1.3 The manufacturing quality of the transformer
In the transformer manufacturing process, many welding spots, long welding seams, difficult welding, welding materials, welding (classification characteristics of welding process equipment) specifications, processes, technology, etc. will affect the welding quality, resulting in pores, sand holes, virtual welding, and desoldering This phenomenon causes the transformer to leak oil.
1.4 The quality of the plate butterfly valve is not good
Another part of the transformer that often leaks is at the plate butterfly valve. The connection surface of the ordinary plate butterfly valve used in the earlier production transformer is relatively rough, thin, and single-layer sealed. It is an obsolete product and is very easy to cause transformer oil leakage.
1.5 Improper installation method
The flange connection is not flat, and the gasket can not be uniformly stressed during installation; the bolts around the gasket are artificially caused to be non-uniformly stressed; the flange joint is deformed and misaligned, so that the force on one side of the gasket is too large, and the force on one side is too small. The sealing gasket on the side with less force is likely to cause leakage due to insufficient compression.