Transformer leakage problem

1 transformer leakage oil causes China's power transformers are mostly oil-immersed transformers, transformer leakage oil leakage phenomenon has occurred from time to time, serious leakage not only reduces the life of the transformer, affecting the system's safety and stable operation, but also The economic benefits of society and users have a serious impact. 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 cracking of weld seams There are many solder joints and long weld seams in transformers, and oil-immersed transformers are based on the welded shells of steel sheets.

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 mostly 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 blowholes, Blisters, imaginary welding, and desoldering cause the transformer to leak oil.

1. 4 Insufficient quality of plate butterfly valves The other part of the transformer that frequently leaks is at the plate butterfly valve. The transformers used earlier, the common plate butterfly valves used are rough, thin and single-layer sealed, and they are phase-out products. Easy to cause 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; Flange joint deformation is misaligned, so that the force on the side of the gasket is too large. When the side 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 shipment Consignment and parts during the process of transportation collide with and improperly hoisted and transported, causing parts to be deformed, welds open, cracks, etc., causing leakage.

2 Types of oil leakage from the transformer 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 oil leakage prevention measures 3.1 Selection of 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 assessing the oil resistance of gaskets, seal aging tests and compatibility tests with transformer oil should generally be performed. Soak them in hot oil at 120°C for 168 hours, and then measure the rate of change in weight, volume, and hardness, and select them. 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 Plugging by electric welding For the pores, blisters, and welds, welds, welds, and cracks that are left in the transformer due to casting, electric 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 and the seals cleaned. Apply sealant on both sides of the seal (generally 609 polymer liquid sealant). After the sealant dries for a certain period of time, the solvent is volatilized and the flange and screw are fastened together.

3. 5 Improve the level of installation technology to prevent the first correction interface of the flange interface from unevenness or deformation due to leakage caused by improper installation method. If the misalignment can not be corrected, the flange can be cut and rewelded. The interface must be parallel. It is advisable that the seal compresses about 1/3 of its thickness during installation.

3. 6 rapid sealing plugging glue stick plugging This method is used for small leakage, leakage of transformers, thin wall of transformer radiator, and leakage points that are not suitable for plugging by electric welding. This method can be used to block leak. 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.