Analysis and Discussion on Oil Leakage of Transformer

With the development of the power industry, improving the performance of power equipment to ensure the reliable operation of the power grid is an urgent need to solve the power generation problem. Therefore, the transformer oil leakage problem can be dealt with promptly and thoroughly. However, it also gradually becomes a measure of the development of the electric power industry and is an essential technical indicator. The oil-immersed power transformer oil leakage phenomenon in the power grid is relatively standard. If the transformer oil leakage phenomenon occurs, it may affect the safe and stable operation of the transformer. How to solve the transformer oil leakage problem: Over the years, the power sector in production has had a significant problem in practice.

I. Cause Analysis of the Transformer Oil Leakage

According to the operating experience, transformer oil leakage usually occurs in the following seven main parts: 1. body cover connection surface; 2. radiator; 3.sampling valve; 4.housing; 5.oil pipe flange surface; 6. transformer base interface; 7.gas relay and so on.

It can be seen that most of the leakage occurs at the flange surface, gaskets, and valves. The flange structure is unreasonable, the quality of the sealing material is poor, the processing technology is poor, and the temperature change of the external environment, the pressure, and so on will cause leakage in the transformer. These factors complement each other and have a common effect. A chain reaction will occur if one has a problem, leading to oil leakage. The following specific analyses have been carried out in practice:

First, the manufacturing process of the flange surface is unreasonable; the leakage point at the interface between the transformer and the radiator accounts for more than half of the total leakage point. The reasons for the leakage are (1) the contact surface there are corrosion, burrs, grooves, and other phenomena; (2) no sealing grooves, unlimited pins; (3) paint and other dirt on the contact surface; in the treatment of paint debris, but also the sealing surface can be scratched out of the scar; (4) sealing the position of the rubber ring and tightness is entirely dependent on empirical judgment, too loose and too tight can lead to leakage.

Second, the most commonly used sealing material is butyl rubber; from gaskets, gaskets made of poor oil resistance age faster, especially at high temperatures, very quickly causing aging cracking and loss of elasticity. Add in the installation process due to uneven sealing surface finish, increasing compression and leakage.

Third is the transformer shell manufacturing process and material quality; if the transformer shell has air holes, trachoma, improper welding, and desoldering, it will lead to transformer oil leakage.

Fourth, the plate butterfly valve connection surface is relatively rough and thin, with only a single-sealing layer, resulting in transformer leakage.

Fifth, the influence of temperature. Outdoor temperature is low in summer if a transformer is not installed. During the summer (temperatures up to 37 ℃), after the operation, the installation of the seals compresses tightly due to the thermal expansion of the metal, increasing the amount of compression. In winter, when the temperature is lowered (as low as -4 ℃), sealing elasticity and compression are reduced, resulting in leakage.

II. Analysis of the Leakage Type

1, air leakage. It is an invisible leakage. Such as the housing head, oil storage cabinet diaphragm, safety airway glass welding bubbles, and other parts of the entry and exit air leakage. The moisture and oxygen in the air will slowly penetrate the body through the leaking parts. The transformer inside and outside the seal is destroyed, resulting in insulation moisture, oil-accelerated aging, and other problems.

2, oil leakage. First, internal leakage. The oil in the enclosure or the tap-changer compartment penetrates the transformer body—second, external leakage. Weld leakage and seal leakage, which are the most likely to occur, are also the most common.

III. The Prevention and Control of Oil Leakage

Through a long period of practice and exploration, we have found some practical methods and measures to deal with transformer oil leakage.

1, sealing surface treatment. On the flange sealing surface, corrosion, burrs, and grooves are taken to strengthen the rust, fill welding, grinding, and other means to improve the flange surface finish so that it meets the requirements. Before installing the gaskets, wipe the flange surface with a clean cloth so there are no oil stains, metal powder, or other impurities, which can quickly form oil and gas channels. Process the corresponding limiting groove and limiting pin on the flange surface to effectively prevent the gaskets from sliding and being excessively compressed, effectively reducing the aging speed of the gaskets and the occurrence of leakage phenomena.

2, the use of new high-temperature, oil-resistant polymer materials—PTFE body seals. The molecular structure of this material is more compact than Buna-N, which can withstand more pressure and shear force and better solve the oil leakage phenomenon caused by the seals' aging.

3, casing upper 6 ~ 10 kV casing upper oil leakage is mainly due to the seal compression being small, the gripper line clamp not being tightened, and heat damage to the seal. The treatment is to replace the gasket or tighten the conductive rod compression nut and the upper wire clamp. If the gripper line clip card is not tight, the slot should be milled larger.

4, sand hole, leakage of welding oil. From the actual situation on site, the eyelet and weld leakage rate is the highest; the reasons are casting, welding, improper procedures, leakage tests not being strict, or material and other problems caused. The treatment is: if the eye is not large, small oil leakage can be loaded to plug, that is, the leakage of oil parts wiped clean, with soap to the oil leakage holes coated with LD-1 type fast-acting plugging sealant, curing can be dissolved in the eye leakage of oil, and the effect is excellent.

When dealing with weld oil leakage, first use a saw blade to clean the leakage parts of the paint, oxide layer, etc., so that it reveals the original color, and then wipe clean with alcohol, sealing the weld with sealant, after curing, oil leakage can be blocked. If the leakage part is too smooth, it can be polished on the surface to increase the adhesion force on the need for power failure welding, which should promote carbon dioxide inert gas welding, automatic arc welding, and other processes; welding should be carried out carefully after the leakage test methods and leakage detection standards.

5, Bleed (oil) screw sealing oil leakage, often due to the use of poorly designed bolts. If the pressure is slight, the seal compression is not enough and leakage; if the pressure is too enormous, the seal exceeds the elastic limit and leakage. The treatment is: to transform the screw structure, that is, in the screw cap, to a round gasket groove, a groove depth of about 3 mm. so that the gasket can be pressed in the groove, so that the gasket is limited in the extrusion under the action of the expansion of the gasket, to obtain a good elasticity of the gasket.

6, a station a main transformer heat sink welding parts of oil leakage phenomenon in many places, although several times by the manufacturer of welding, have yet to be fully managed. After a series of tests, in the case of non-stop flow, the use of modified acrylate adhesive to the leakage point of treatment achieved good results. Specific practices are described as follows:

(1) the use of modified acrylic adhesive to deal with the advantages of leakage. Using modified acrylate adhesive to deal with oil injection equipment leakage problems, the operation is simple and, convenient, and easy to learn and master. Avoid the danger of transformer oil burning caused by high-temperature welding, avoid the possibility of high temperature leading to carbonization of transformer oil, and it can be carried out without interrupting power treatment to ensure that the power supply is still reliable.

(2) the use of modified acrylic vinegar glue to eliminate leaks. First, with detergent or washing powder, the oil leakage was cleaned, drying with a coarse emery cloth to remove the leakage of paint, and then with a fine emery cloth to grind further so that the leakage of flat, smooth, clean, no stains. If the leakage time is longer and there is more deposited mud, you can use a razor blade to remove the mud, wash it with detergent, and dry it with a cloth and sandpaper.

Suppose you find heavy oil oozing after cleaning (more than ten drops per minute). In that case, it can be modified with an acrylic vinegar adhesive mixture coated directly into the gap, first to stop the oil oozing, and then use the tool to apply the adhesive scraping, and then cleaning and sanding; this stage is called priming. After completion of priming, the modified acrylate adhesive will be evenly coated into the primer surface, stopped for 1 minute without sticking, and then the hand will evenly press the adhesive so that the adhesive effectively into the gap, blocking the oil seepage point. After treatment and observation for a month, the leak is no longer oil stains, and then the leak is sprayed with anti-rust paint.

7, choose good performance, high quality, advanced technology transformer. Regular replacement of gaskets, even if the gaskets have not exceeded the service life, should be replaced before the aging failure so as not to cause leakage deterioration.

8. Good personnel quality is essential to solving the leakage of one key. Even with the same transformer, installation and maintenance personnel are different, and the results are completely different. Installation and maintenance team quality is an essential factor in reducing transformer leakage.

In recent years, we have taken a series of measures to prevent oil leakage so that the leakage rate in the overhaul of transformers has been dramatically reduced. In practice, it has been proved that the oil leakage problem in transformers can be solved entirely as long as careful inspection and analysis are carried out and attention is paid to the quality of installation and maintenance, thereby improving the safety and reliability of transformer operation. Continuous improvement, a summary of prevention and control measures, and a transformer oil leakage rate will be significantly reduced to ensure the safety of the transformer's operation for the enterprise, the community, and the user in achieving economic benefits.