Main Power Transformer Oil Leakage Problem

Most of my country's main power transformers are oil-immersed transformers. Over the years, oil leakage of transformers has occurred from time to time. Severe leakage not only reduces the service life of transformers, but also affects the safe and stable operation of the system. It also affects the economic benefits of society and users. severe impact. In recent years, in the process of overhauling the main transformers and plant transformers of various power plants, the reasons for oil leakage of transformers are found as follows:

Rubber seal failure and weld cracking

The transformer has many welding points and long welding seams, while the oil-immersed transformer is an assembly of various welding and connections based on the welded steel shell.

A 31500kVA main power transformer has a total of more than 70 welding points, and the total length of the welding seam is about 20m, so there can be more leakage methods. The reasons for direct leakage are failure of rubber seals and cracking of welds, pores, slag inclusions, etc.

Aging, cracking and deformation of sealant parts

Transformer leakage mostly occurs at the connection, and more than 95% is mainly caused by sealant parts. The quality of the sealant mainly depends on its oil resistance. If the oil resistance is poor, the aging speed will be faster, especially at high temperature, the aging speed will be faster, which will easily lead to the aging and cracking of the seal. Metamorphosis, deformation, and failure, resulting in transformer oil leakage.

The quality of the main power transformer

During the production process of the transformer, there are many welding points in the fuel tank, long welding seams, difficult welding, welding materials, welding (classification characteristics of welding skills and equipment) standards, skills, skills, etc. will affect the welding quality, resulting in pores, blisters, virtual welding, and desoldering. The appearance thus makes the transformer leak oil.

Poor quality of plate butterfly valve

Another part of the transformer that often leaks is at the plate butterfly valve. The transformers produced earlier use a generally rough, thin, single-layer seal, which is a screening product, and it is easy to cause oil leakage in the transformer.

Improper installation

The flange joints are not flat, and the sealing gasket cannot be uniformly stressed during installation; the artificially formed bolts near the gasket are not uniformly stressed; the flange joints are deformed and dislocated, so that the force on one side of the gasket is too large, and the force on one side is too small. The gasket on the side with less force will easily lead to leakage due to the lack of tightening amount. This phenomenon often occurs at the connection of the gas relay and the connection between the radiator and the body; another point is that when the gasket is installed, the amount of compression is insufficient or too large. When the amount of compression is insufficient, the operating temperature of the transformer increases and the oil becomes thinner, resulting in Transformer oil seeps, the amount of compression is too large, the gasket is severely deformed, and the aging accelerates and shortens the service life.

wrong mail

In the process of mailing and construction and transportation, parts are bumped and incorrectly hoisted and transported, resulting in parts being damaged and deformed, welding openings, cracks, etc., resulting in leakage.

2 Types of transformer oil leakage

2.1 Air leakage

It's an invisible leak. Such as the leakage of the air in and out of the head of the casing, the partition of the oil conservator, the glass of the safety airway and the trachoma of the welding seam. Moisture and oxygen in the air will slowly penetrate into the body through the leaking parts, and the seal between the inside and outside of the transformer will be damaged, causing problems such as insulation damping and accelerated oil aging.

2.2 Oil leakage

2.2.1 Internal leakage.

The oil in the bushing or the oil in the on-load tap-changer chamber leaks into the transformer body.

2.2.2 External leakage.

Weld leakage and seal leakage are the most common and common leakage symptoms.

3 Preventive measures for transformer oil leakage

3.1 Select seals with good raw materials

When the main power transformer is repaired and disposed of leakage, seals with high temperature resistance and oil resistance should be selected. The most commonly used sealing material in the domestic transformer industry is nitrile rubber, and its oil resistance mainly depends on the content of acrylonitrile in the nitrile rubber. In general, nitrile rubber with Shore hardness between 70 and 80 should be selected. When judging the oil resistance of the gasket, usually the aging test of the gasket and the compatibility test with the transformer oil should be done, and it should be immersed in hot oil at 120 ° C for 168 hours, and then the change rate of its weight, volume and hardness should be measured. The deformation is not large, and it fits standard seals.

3.2 Choose high quality butterfly valve

Butterfly valve choose vacuum eccentric butterfly valve. Compared with ordinary butterfly valves, vacuum eccentric butterfly valves have made great progress in mechanical strength and surface finish, and this product also has one of the biggest advantages, that is, the double-layer seal is used at the interface with the transformer flange, which eliminates the need for Solve the problem of oil leakage at the transformer interface.

3.3 Use electric welding to plug leaks

For the voids, blisters, welds, and solder joints left by the transformer due to casting, the virtual welding, desoldering, and cracks can be plugged by electric welding.

Leakage points should be identified before plugging welding. If the leakage point is smaller, the leakage point can be killed directly by electric welding; if the leakage point is larger, asbestos rope or metal filler should be filled first, and then surfacing nearby, and then use a small electrode High current fast arc ignition repair welding.

3.4 Standard seal replacement skills

For main power transformer of different types and capacities, whether it is flange connection or threaded connection, it is necessary to remove dust and rust on the connection surface before replacing the seal. Apply sealant (usually 609 polymer liquid sealant) on the surface. After the sealant is dry for a period of time, the solvent evaporates, and then the flange and screws are connected and fastened.

3.5 Improve the technical level of installation and eliminate leakage caused by improper installation methods

If the flange interface is uneven or deformed and misaligned, the interface should be calibrated first. If the dislocation is serious and cannot be calibrated, the flange can be cut off and re-welded. It is necessary to ensure that the interface is parallel. When installing, it is advisable to shrink the gasket by about 1/3 of its thickness.

3.6 Fast sealing and plugging glue stick to plug leakage

This method is used for small leakage and dripping of transformers. This method can be used to plug the leakage points where the radiator tube wall of the transformer is thin and it is not suitable to be treated by electric welding. When using the plugging glue stick to plug the leakage, it is necessary to completely remove the oil, paint, and oxides in the plugging part, so that the metal can reveal its nature. Then adjust the plugging glue according to the proportion, and plug the leaking parts until the leakage stops.

4 Summary

With the development of the power industry, how to improve the performance of power equipment and ensure the reliable operation of the power system is an urgent problem that needs to be solved in power production. Therefore, whether the oil leakage problem of transformers can be solved in a timely and complete manner has gradually become a problem. Measure important technical indicators for the development of the power industry. In recent years, after dealing with the oil leakage problem of the main transformer and the factory transformer, and continuously improving and summarizing the prevention and control measures, the oil leakage rate of the transformer has been greatly reduced, which has provided a guarantee for the safe operation of the transformer, and obtained the company, society and users. economic benefits.