1 Analysis of the causes of leakage of transformer oil The power transformers in China are mostly oil-immersed transformers. Oil leakage from transformers has occurred from time to time. Severe leakage not only reduces the service life of the transformer, but also affects the safe and stable operation of the system. It has a serious impact on the economic benefits of society and users. In recent years, during the overhaul of the main transformers and factory transformers in various power plants, we discovered that the causes of transformer oil leakage were as follows:
1.1 Failure of rubber seals and weld cracking Transformers have many welds and long welds, while oil-immersed transformers are a collection of welded and connected assemblies based on welded steel shells.
The total number of solder joints of a 31,500 kVA transformer is more than 70, and the total length of the weld is about 20 m. Therefore, there may be more leakage paths. The reason for direct leakage is the failure of rubber seals and cracking of welds, pores, and slag inclusions.
1.2 Aging, cracking, and deformation of the sealant The transformer leakage occurs at the joint, and more than 95% is mainly caused by the sealant. The quality of the sealant depends mainly on its oil resistance, poor oil resistance, and the aging rate is faster. Especially at high temperatures, the aging rate is faster and can easily cause aging and cracking of the seal. Deterioration, deformation, and even failure, causing the transformer to leak oil.
1.3 Transformer manufacturing quality In the manufacturing process, transformers have many solder joints, long welding seams, difficult welding, welding materials, welding (classification features of welding process equipment) specifications, processes, technologies, etc. will affect the quality of welding, resulting in pores, trachoma, Welds and solderings cause the transformer to leak oil.
1.4 Insufficient quality of the plate butterfly valve The other part of the transformer that often leaks occurs at the plate butterfly valve. The common plate butterfly valve that was used earlier has a rough, thin, single-layer seal, and is a phase-out product. It is easily caused. Transformer leakage oil.
1.5 Improper installation methods Flange joints are uneven. When installed, the gasket can not be evenly stressed around; artificially create uneven force on the bolts around the gasket; the flange joint deformation is misaligned, so that the force on one side of the gasket is too large, and one side is affected. If the force is too small, the seal on the side with less force can easily cause leakage due to insufficient compression. This phenomenon occurs mostly 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 compression is insufficient or excessive. When the compression is insufficient, the transformer operating temperature rises and the oil thins, causing the transformer. Oil leakage, large amount of compression, serious deformation of the gasket, accelerated aging shortened service life.
1.6 Improper consignment During the consignment and construction process, components collide with and improperly hoisted and transported, causing parts to be deformed, welded joints open, cracks, etc., causing leakage.
2 Types of Oil Leakage in Transformers 2.1 Air leakage is an invisible leakage. Such as the casing head, the diaphragm of the oil conservator, the glass of the safety airway, and the leaks of the air in and out of the weld seam. The moisture and oxygen in the air will slowly penetrate the body through the leaked parts, and the internal and external seals of the transformer will be destroyed, causing problems such as moisture in the insulation and accelerated aging of the oil.
2.2 Oil leakage 2.2.1 Internal leakage.
The oil in the bushing or the oil in the on-load tap-changer room leaks into the transformer body.
2.2.2 External leakage.
Weld leaks and leakage of seals are the most common and most common leaks.
3 transformer leakage oil prevention measures 3.1 choose a good seal material transformer repair and handling leakage, should choose high temperature, good oil seals. The most commonly used sealing material in the domestic transformer industry is nitrile rubber. Its oil resistance performance mainly depends on the content of acrylonitrile in nitrile rubber. The higher the acrylonitrile content, the better the oil resistance, and the greater the hardness, the less likely to be deformed. In general, Nitrile rubber with Shore hardness between 70 and 80 should be selected. When evaluating the oil resistance of gaskets, seal aging test and compatibility test with transformer oil should generally be done. Soak it in hot oil at 120°C for 168 hours, and then measure the change rate of its weight, volume and hardness. Little deformation, in line with the standard seals.
3.2 Select high-quality butterfly valve Choose ZF80 vacuum eccentric butterfly valve. Compared with ordinary butterfly valve, vacuum eccentric butterfly valve has great improvement in mechanical strength and surface finish. Moreover, this product has one of the biggest advantages, that is, it uses a double seal at the interface with the flange of the transformer. Leakage at the transformer interface.
3.3 The use of welding plugging For transformers due to the casting of the pores, blisters, welds, solder joints, the emergence of welding, desoldering, cracking, welding can be used for plugging.
The leakage point should be found before plugging, and the leakage point can be directly destroyed by welding if the leakage point is smaller. The asbestos rope or metal packing should be filled first in the larger leakage point, and then surfacing in the surrounding area. Then the small welding rod is used. High current fast arc welding.
3.4 Specification Seal replacement process For transformers of different types and capacities, whether flanged or threaded, the dust and rust on the connection surface must be removed before the seals are replaced. The seals are cleaned and sealed. The two sides are coated with a sealant (generally 609 polymer liquid sealant). After the sealant is dried for a period of time after the solvent evaporates, tighten the flange and the screw.
3.5 to improve the installation level, to prevent leakage caused by improper installation of the flange interface uneven or deformation misalignment of the first correction interface, misalignment can not be corrected can be cut off the flange re-welding, must ensure parallel interface. When mounting, the compression of the gasket is about 1/3 of its thickness.
3.6 Rapid Sealing Plugging Rods Plugging This method is used for small leakage and leakage of transformers. The leakage of the transformer radiators with thinner walls and leakage plugging methods that are not suitable for plugging can be blocked by this method. When plugging with a plugging glue stick, the oil, paint, and oxide in the plugged area must be completely removed to expose the metal. Then adjust the amount of plugging glue according to the ratio, and plug the leaked part until it does not leak.
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 to be solved in power production. Therefore, whether the oil leakage problem of the transformer can be solved in a timely and thorough manner can also be solved. Gradually become an important technical indicator for measuring the development of the power industry. In recent years, we have continuously improved and summed up prevention and control measures through the treatment of oil changes in the main transformer and the plant. The leakage rate of the transformer has been greatly reduced, providing a guarantee for the safe operation of transformers for enterprises, communities and users. Has achieved economic benefits.
1.1 Failure of rubber seals and weld cracking Transformers have many welds and long welds, while oil-immersed transformers are a collection of welded and connected assemblies based on welded steel shells.
The total number of solder joints of a 31,500 kVA transformer is more than 70, and the total length of the weld is about 20 m. Therefore, there may be more leakage paths. The reason for direct leakage is the failure of rubber seals and cracking of welds, pores, and slag inclusions.
1.2 Aging, cracking, and deformation of the sealant The transformer leakage occurs at the joint, and more than 95% is mainly caused by the sealant. The quality of the sealant depends mainly on its oil resistance, poor oil resistance, and the aging rate is faster. Especially at high temperatures, the aging rate is faster and can easily cause aging and cracking of the seal. Deterioration, deformation, and even failure, causing the transformer to leak oil.
1.3 Transformer manufacturing quality In the manufacturing process, transformers have many solder joints, long welding seams, difficult welding, welding materials, welding (classification features of welding process equipment) specifications, processes, technologies, etc. will affect the quality of welding, resulting in pores, trachoma, Welds and solderings cause the transformer to leak oil.
1.4 Insufficient quality of the plate butterfly valve The other part of the transformer that often leaks occurs at the plate butterfly valve. The common plate butterfly valve that was used earlier has a rough, thin, single-layer seal, and is a phase-out product. It is easily caused. Transformer leakage oil.
1.5 Improper installation methods Flange joints are uneven. When installed, the gasket can not be evenly stressed around; artificially create uneven force on the bolts around the gasket; the flange joint deformation is misaligned, so that the force on one side of the gasket is too large, and one side is affected. If the force is too small, the seal on the side with less force can easily cause leakage due to insufficient compression. This phenomenon occurs mostly 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 compression is insufficient or excessive. When the compression is insufficient, the transformer operating temperature rises and the oil thins, causing the transformer. Oil leakage, large amount of compression, serious deformation of the gasket, accelerated aging shortened service life.
1.6 Improper consignment During the consignment and construction process, components collide with and improperly hoisted and transported, causing parts to be deformed, welded joints open, cracks, etc., causing leakage.
2 Types of Oil Leakage in Transformers 2.1 Air leakage is an invisible leakage. Such as the casing head, the diaphragm of the oil conservator, the glass of the safety airway, and the leaks of the air in and out of the weld seam. The moisture and oxygen in the air will slowly penetrate the body through the leaked parts, and the internal and external seals of the transformer will be destroyed, causing problems such as moisture in the insulation and accelerated aging of the oil.
2.2 Oil leakage 2.2.1 Internal leakage.
The oil in the bushing or the oil in the on-load tap-changer room leaks into the transformer body.
2.2.2 External leakage.
Weld leaks and leakage of seals are the most common and most common leaks.
3 transformer leakage oil prevention measures 3.1 choose a good seal material transformer repair and handling leakage, should choose high temperature, good oil seals. The most commonly used sealing material in the domestic transformer industry is nitrile rubber. Its oil resistance performance mainly depends on the content of acrylonitrile in nitrile rubber. The higher the acrylonitrile content, the better the oil resistance, and the greater the hardness, the less likely to be deformed. In general, Nitrile rubber with Shore hardness between 70 and 80 should be selected. When evaluating the oil resistance of gaskets, seal aging test and compatibility test with transformer oil should generally be done. Soak it in hot oil at 120°C for 168 hours, and then measure the change rate of its weight, volume and hardness. Little deformation, in line with the standard seals.
3.2 Select high-quality butterfly valve Choose ZF80 vacuum eccentric butterfly valve. Compared with ordinary butterfly valve, vacuum eccentric butterfly valve has great improvement in mechanical strength and surface finish. Moreover, this product has one of the biggest advantages, that is, it uses a double seal at the interface with the flange of the transformer. Leakage at the transformer interface.
3.3 The use of welding plugging For transformers due to the casting of the pores, blisters, welds, solder joints, the emergence of welding, desoldering, cracking, welding can be used for plugging.
The leakage point should be found before plugging, and the leakage point can be directly destroyed by welding if the leakage point is smaller. The asbestos rope or metal packing should be filled first in the larger leakage point, and then surfacing in the surrounding area. Then the small welding rod is used. High current fast arc welding.
3.4 Specification Seal replacement process For transformers of different types and capacities, whether flanged or threaded, the dust and rust on the connection surface must be removed before the seals are replaced. The seals are cleaned and sealed. The two sides are coated with a sealant (generally 609 polymer liquid sealant). After the sealant is dried for a period of time after the solvent evaporates, tighten the flange and the screw.
3.5 to improve the installation level, to prevent leakage caused by improper installation of the flange interface uneven or deformation misalignment of the first correction interface, misalignment can not be corrected can be cut off the flange re-welding, must ensure parallel interface. When mounting, the compression of the gasket is about 1/3 of its thickness.
3.6 Rapid Sealing Plugging Rods Plugging This method is used for small leakage and leakage of transformers. The leakage of the transformer radiators with thinner walls and leakage plugging methods that are not suitable for plugging can be blocked by this method. When plugging with a plugging glue stick, the oil, paint, and oxide in the plugged area must be completely removed to expose the metal. Then adjust the amount of plugging glue according to the ratio, and plug the leaked part until it does not leak.
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 to be solved in power production. Therefore, whether the oil leakage problem of the transformer can be solved in a timely and thorough manner can also be solved. Gradually become an important technical indicator for measuring the development of the power industry. In recent years, we have continuously improved and summed up prevention and control measures through the treatment of oil changes in the main transformer and the plant. The leakage rate of the transformer has been greatly reduced, providing a guarantee for the safe operation of transformers for enterprises, communities and users. Has achieved economic benefits.
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