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1.1 Failure of rubber seals and weld cracking

Special transformer transformer welding points, long weld, and oil immersed special transformer transformer is a steel plate welded shell based on a variety of welding and connection.

The total welding spot of a QB-5000/2 oil-immersed traction transformer reaches more than 70 places, and the total weld length is about 20m, so there may be more leakage paths. The cause of direct leakage is the failure of rubber seals and weld cracking, porosity, slag inclusion and so on.

1.2 Aging, cracking and deformation of sealant parts

Special transformer leakage occurs in the connection, and more than 95 % is mainly caused by sealant parts.

The quality of sealant mainly depends on its oil resistance. If the oil resistance is poor, the aging speed is faster. Especially at high temperature, the aging speed is faster.

1.3 Manufacturing quality of special transformers

In the manufacturing process of special transformer, the tank welding spot is much, the weld is long, the welding is difficult, the welding material, the welding (the classification characteristics of the welding process equipment) specifications, the process, the technology and so on will affect the welding quality, resulting in the porosity, the sand hole, the virtual welding, the welding phenomenon, so that the special transformer leakage oil.

1.4 Plate butterfly valve quality is not good

Special transformer another leakage often occurs in the plate butterfly valve, earlier production of transformers, the use of ordinary plate butterfly valve connection surface is rough, thin, single-layer seal, is a eliminated product, easy to cause transformer leakage oil.

1.5 Improper Installation Method

The flange connection is uneven, and the sealing gasket can not be evenly stressed around the installation; Artificial causes the bolt around the gasket uneven force; The flange joint deformation dislocation, so that the force on one side of the gasket is larger, the force on the other side is smaller, the force on the side of the gasket is smaller because of the lack of compression, it is easy to cause leakage.

This phenomenon occurs in the gas relay connection and radiator and body connection; Another point is that when the gasket is installed, the compression amount is insufficient or too large. When the compression amount is insufficient, the transformer operation temperature rises and the oil becomes thinner, resulting in special transformer oil seepage, large compression amount, serious deformation of the gasket, and accelerated aging, shortening of the service life.

1.6 Improper Consignment

The collision of parts and components in the process of consignment and construction transportation and incorrect lifting and transportation, resulting in the collision and deformation of parts, welding opening, cracks and so on, causing leakage.

2. Type of leakage oil of special transformer

2.1 Air Leakage

It's an invisible leak. For example, the leakage of air in and out of the casing head, the diaphragm of the oil storage tank, the glass of the safety airway and the sand hole of the weld. The moisture and oxygen in the air will slowly penetrate into the body through the leaking part, and the sealing inside and outside of the transformer will be damaged, resulting in moisture insulation and accelerated aging of oil and other problems.

2.2 Oil Leakage

2. 2. 1 Internal leakage.

Oil in the casing or oil in the on-load pressure regulating tap changer chamber leaks into the transformer body.

2. 2. 2 External leakage.

Weld leakage and seal leakage, which is the most common leakage phenomenon.

3. Preventive measures for oil leakage of special transformer

3. 1 Choose seals with good material

Transformer maintenance and treatment of leakage, should choose high temperature resistance, good oil resistance sealing parts. Domestic special transformer industry the most commonly used sealing material for nitrile rubber, its oil resistance mainly depends on the acrylonitrile content of nitrile rubber, the higher the acrylonitrile content, the better the oil resistance, the greater the hardness, the more difficult to deformation.

In general, we should choose the Shao hardness between 70 and 80 nitrile rubber. When identifying the oil resistance of the gasket, it is generally necessary to do the aging test of the gasket and the compatibility test with the special transformer oil, soak it in the hot oil of 120℃ for 168h, and then measure the change rate of its weight, volume and hardness, select the sealing parts with little deformation and in line with the standard.

3. 2 Select high quality butterfly valves

ZF80 vacuum eccentric butterfly valve is selected. Compared with the ordinary butterfly valve, the vacuum eccentric butterfly valve has been greatly improved in mechanical strength and surface finish, and the biggest advantage of this product is that it adopts a double seal at the transformer flange interface, so as to eliminate the leakage of oil at the transformer interface.

3. Use electric welding to stop leakage

For the special transformer due to the casting of pores, sand holes, weld, welding spot welding, welding, crack, available welding plugging.

The leakage point should be found before plugging welding, and the leakage point can be killed directly with electric welding. If the leakage point is large, it should be filled with asbestos rope or metal filler first, and then surfacing around, and then using small electrode and high current quick arc welding.

4. Standardize the sealing parts replacement process

For different models and different capacities of special transformers, whether flange connection or thread connection, the dust and rust on the connecting surface must be removed before replacing the seals. After cleaning the seals, both sides of the seals are coated with sealant (generally 609 polymer liquid sealant). After the sealant is dried for a period of time, the solvent volatilized. Fasten the flange and screw.

3. 5 Improve the installation technology level and eliminate leakage caused by improper installation methods

If the flange interface is uneven or deformed and misaligned, correct the interface first. If the misalignment is serious and cannot be corrected, cut off the flange and weld it again. Ensure that the interface is parallel. When installing the sealing gasket compression is about 1/3 of its thickness is appropriate.

3. 6 Quick sealing plugging glue stick plugging

This method is used for small leakage, drip leakage of transformer, special transformer radiator tube wall is thin, and not suitable for welding plugging method of leakage point can be taken this method. When plugging with plugging glue stick, the oil, patent leather and oxide of the plugging part must be completely removed to make the metal show its natural color. Then adjust the plugging glue according to the ratio, plugging the leakage part until it does not leak.