Discussion on leakage of transformer

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Talking about the leakage of transformer

the leakage of transformer is a common problem of transformer failure, especially some transformers that have been in operation for a long time are more common. The light ones pollute the appearance of the equipment and affect the beauty, and the heavy ones threaten the safe operation of the equipment and even the lives of personnel. The leakage of transformer includes inlet and outlet air (except the air normally entering through the moisture absorber) and oil leakage. There are two main reasons for leakage: on the one hand, it is hidden in the process of transformer design and manufacturing technology; On the other hand, it is caused by improper installation and maintenance of the transformer

1 in and out air

in and out air is an invisible form of leakage. For example, the inlet and outlet air of the casing head, the diaphragm of the oil conservator, the glass of the safety airway, weld sand holes and steel sand inclusions are invisible. Over the years, the main malignant accidents in the power system are mostly winding burns and serious damage to the transformer body due to the short circuit at the low-voltage outlet of the transformer. Among them, the winding burn accidents caused by the reduction of turn insulation mostly occur under normal working voltage. This kind of accident is mostly caused by the damp of winding insulation caused by leakage and entering humid air. The company said that a branch like creepage accident along the cardboard in China was caused by the moisture of the cardboard, and the main reason was the leakage of the safety airway glass. In recent years, the pressure relief valve protection device has been adopted for newly delivered large transformers, replacing the safety air duct. Therefore, it is very important to prevent the air from contacting the internal insulation of the transformer, especially at the casing head, oil conservator diaphragm and safety airway glass. During the installation and overhaul of the transformer, its quality should be guaranteed, and it should be carefully inspected and maintained during the annual inspection, preventive test and antifouling cleaning of the transformer. The problems of weld sand holes and lax sealing should also be included. It should be emphasized that the sand holes in the weld and the lax sealing of the flange not only show oil leakage, but also air leakage into the transformer. The moisture and oxygen in the air will slowly penetrate into the body through the oil leakage part, that is to say, the isolation between the inside and outside of the transformer is destroyed, both oil leakage and air intrusion. Of course, in this case, the invasion of air is certainly weak, but attention should be paid to the long-term cumulative damage to the internal insulation of the transformer

2 classification of oil leakage

youth is for struggle; In the future, the oil leakage of the transformer can be divided into internal leakage and external leakage, and the external leakage can be divided into weld leakage and sealing surface leakage

(1) internal leakage. The most common internal leakage is that the oil in the oil filled bushing and the oil in the oil chamber of the on load voltage regulating device switch leak to the transformer body. The normal oil level of the oil filled bushing is higher than the oil level of the transformer body. If the sealing part of the bushing factory is not sealed tightly, there will be no oil in the bushing under the action of oil pressure difference, which will affect the safe operation of the equipment. Generally, this situation can be eliminated by lifting out the casing and fastening the corresponding sealing part at the lower part. If the rubber pad is found to be aging and lose elasticity, it should be replaced. Previously, it was found that the bushing of a transformer

phase had no oil surface. During normal inspection, there was no oil on its surface, which was determined to be leakage to the transformer body. During treatment, the bushing was lifted out. After testing with clay, it was found that there was oil leakage at the oil plug at the lower part of the bushing. After fastening the oil plug, it was tested with clay, and there was no oil leakage. Put the casing in place and add oil to the normal oil level. After many rounds of inspection, the effect is good

(2) leakage. External leakage is divided into weld leakage and sealing surface leakage:

① weld leakage. Weld leakage is caused by sand holes in the welding part of the steel plate. If leakage is found on the upper part of the transformer oil tank, it can be welded as long as a small amount of oil is discharged; When leakage is found at the lower part of the oil tank, due to the large waste of oil discharged from the lifting core and limited by the site conditions, the method of repair welding with oil can be adopted. The repair welding with oil should be carried out when the oil leakage is not significant. For example, there are sand holes in the weld between the oil drain valve of Nanmen electric drainage station and the transformer body. This weld cannot be seen with the naked eye when the transformer is running, and the oil seeps outward through the sand holes in the weld. When handling, first clean it with a wire brush, then rinse it with clean water, and finally repeatedly clean it with a clean cloth. When finding the exact position of the leakage point, repeatedly wipe it with wet soap at the leakage part, and then repair welding can be carried out after the purpose of stopping leakage is achieved. After on-site treatment, the oil leakage disappeared and did not affect the normal operation of the transformer. If the oil leakage is large, the vacuum pumping and oil drainage method should be used to create negative pressure before welding. The vacuum of negative pressure should not be too high, and the internal and external pressure should be equal to avoid attracting molten iron during welding

gas welding is generally prohibited for repair welding with oil. Thinner welding rods such as 422 and 425 are suitable for welding. During repair welding, the oil stains on the welding position should be eliminated, and it is best to wash with alkaline water and then wipe dry. Pay attention to prevent penetration and ignition during welding, and the welding part must be above the oil level. Intermittent and rapid spot welding shall be adopted during welding, and the arc burning time shall be controlled within S. continuous welding for a long time is absolutely not allowed. When repairing the air gap with serious oil leakage, it can be blocked or riveted with iron wire before welding. When welding near other vulnerable parts of the sealing rubber gasket, cooling and protective measures and fire prevention treatment should be taken

② the sealing surface leaks. The products cover general plastics, engineering plastics, special engineering plastics and other fields, and the leakage of sealing surface is relatively complex, so it is necessary to analyze specific problems. The bolts can be tightened simply on site, but preventing the leakage of the sealing surface should be regarded as an important work during the overhaul or installation of the transformer

3 conclusion

about the leakage of the sealing surface, only a few common points are summarized above. In fact, there are many reasons for the leakage, such as the sealing surface is horseshoe shaped, the design of some oil plug sealing surfaces is unreasonable, and the flange steel plate of the sealing surface is thin. In different situations, the weight of the square body to solve the problem can be greatly reduced, and the method is also different, which requires us to carefully analyze and summarize in actual work, and do a better job in eliminating leakage

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