Fault Analysis and Treatment Measures of Power Transformer I

　　At present, the most widely used power transformers are oil-immersed transformers and dry-type resin transformers. The insulation of power transformers is the insulation system composed of transformer insulation. It is the basic condition for the normal operation and operation of the transformer. The service life of the transformer is Insulation material (ie oil paper or resin, etc.) determined by the life.

　　Practice has proved that most of the transformer damage and failure are caused by damage to the insulation system. According to statistics, due to various types of insulation failure occurred in the accident accounted for more than 85% of all transformer accidents. For the normal operation and attention to the maintenance of the management of the transformer, the insulating material has a very long service life. Therefore, the protection of the normal operation of the transformer and strengthen the reasonable maintenance of the insulation system, to a large extent to ensure that the transformer has a relatively long service life, and preventive and predictive maintenance is to improve the life of the transformer and improve the reliability of power supply key The

　　In the oil-immersed transformers, the main insulating material is insulating oil and solid insulation materials, paperboard and wood blocks, etc. c so-called transformer insulation aging, that is, these materials are affected by environmental factors decomposition, reduce or lose the insulation strength.

　　Solid paper insulation failure Solid paper insulation is one of the main parts of oil-immersed transformer insulation, including: insulation paper, insulation board, insulation pad, insulation roll, insulation banding, etc. The main component is cellulose, chemical expression (C6H10O6 ) N, where n is the degree of polymerization. Generally, the degree of polymerization of new paper is about 1300, and when it reaches about 250, the mechanical strength has been reduced by more than half, and the degree of polymerization at the end of life is 150 to 200. After the aging of the insulating paper, the degree of polymerization and tensile strength will be gradually reduced, and generate water, CO, CO2, followed by furfural (furan formaldehyde). Most of these aging products are harmful to electrical equipment, will reduce the breakdown voltage and volume resistivity of insulating paper, the dielectric loss increases, the tensile strength decreases, and the metal material in the equipment is very corroded. Solid insulation has irreversible aging properties, its mechanical and electrical strength of the aging reduction can not be restored. The life of the transformer depends mainly on the life of the insulating material, so the oil-immersed transformer solid insulation material should have both good electrical insulation properties and mechanical properties, and after years of operation, its performance is slow, that is, aging characteristics.

　　1, the performance of paper fiber material. Insulating paper fiber material is the most important insulating component material in oil-immersed transformers. The paper fiber is the basic solid tissue component of the plant. The atoms of the constituent material molecules have positively charged nuclei and negatively charged electrons running around the nucleus. Conductor is different from the insulating material in almost no free electrons, insulators in the very small conductance mainly from the ion conductivity. The cellulose is composed of carbon, hydrogen and oxygen, so that there is a potential for the formation of water due to the presence of hydroxide in the molecular structure of the cellulose, so that the paper fibers have water-containing properties. In addition, these hydrogen atoms can be considered to be surrounded by various polar molecules (such as acids and water), which are combined with hydrogen bonds, making the fibers vulnerable to damage: the fibers often contain a certain proportion (about 7% ), These impurities include a certain amount of water, because the fiber was colloidal nature, so that the water can not be completely removed. This also affects the performance of paper fiber.

　　Polar fibers are not only easy to absorb moisture (moisture to make strong polar media), and when the paper fiber absorbs water, the interaction between the hydroxyl force weakened, the fiber structure is unstable under the conditions of mechanical strength sharply deteriorated , Therefore, the paper insulation parts are generally dried or vacuum dry treatment and immersion paint or insulating paint before use, the purpose of dipping paint is to keep the fiber wetting to ensure that it has a higher insulation and chemical stability and High mechanical strength. At the same time, the paper is sealed, the paper can reduce the absorption of moisture on the paper, to prevent oxidation of materials, but also to fill the gap, to reduce the insulation performance may be possible, resulting in partial discharge and electric breakdown of the bubble. But some that dip paint and then dip oil, there may be some paint will slowly dissolve in the oil, affecting the performance of oil, the application of such paint should be sufficient to note.

　　Of course, the different properties of different fiber materials and the same composition of the different quality of fiber materials, the impact of the size and performance are different, such as cotton fiber composition of the highest, the most strong fiber in cannabis, some imported insulating paperboard processing because of its good Performance is better than some of the materials made of cardboard. Most of the transformer insulation materials are used in various types of paper (such as paper, cardboard, paper pressure molding, etc.) for insulation. Therefore, in the transformer manufacturing and maintenance of a good choice of fiber materials, insulation paper material is very important. The special advantages of fiber paper is practical, low price, easy to use, in the temperature is not high when the molding and processing simple and flexible, and light weight, moderate strength, easy to absorb impregnated materials (such as insulating paint, transformer oil, etc.).

　　2, the mechanical strength of paper insulation material. Oil-immersed transformers Select the most important factors for paper insulation. In addition to paper fiber composition, density, permeability and uniformity, it also includes mechanical strength requirements, including tensile strength, stamping strength, tear strength and toughness:

　　① tensile strength: the requirements of paper fiber by the tensile load, with a tolerance can not be pulled off the maximum stress

　　② Stamping strength: the requirement that the paper fibers be resistant to stress without being broken.

　　③ tear strength: the required paper fiber tear required to meet the appropriate standards.

　　④ toughness: paper folding or cardboard bending strength to meet the corresponding requirements.

　　Determine the solid insulation performance can be measured to measure the degree of polymerization of paper or cardboard, or the use of high performance liquid chromatography analysis of oil in the determination of furfural content in order to analyze the transformer internal failure, whether it involves solid insulation or the presence of coil insulation caused by local aging Of the low temperature overheating, or to determine the degree of solid insulation aging. Insulation material on the paper fiber in the operation and maintenance, should pay attention to control the transformer rated load, requiring the operating environment air circulation, heat dissipation conditions, to prevent the transformer temperature rise and the cabinet lack of oil. But also to prevent oil pollution, deterioration caused by accelerated aging of the fiber, and damage the transformer insulation performance, service life and safe operation.

　　3, the deterioration of paper fiber material. Mainly includes three aspects: ① fiber embrittlement. When the excessive heat from the fiber material from the separation, but also accelerate the embrittlement of fiber materials. As the paper brittle peeling, in the mechanical vibration, electric stress, operating waves and other impact under the influence of insulation failure may occur and the formation of electrical accidents.

　　② mechanical strength of fiber material decreased. The mechanical strength of the fiber material decreases with the extension of the heating time. When the transformer heats up the moisture of the insulating material again, the insulation resistance value may become higher, but the mechanical strength will be greatly reduced, the insulating paper will not resist the short circuit current Or impact load and other mechanical forces.

　　③ shrinkage of the fiber material itself. The fibrous material shrinks after embrittlement, reducing the clamping force, which may cause shrinkage to move the transformer windings in the electromagnetic vibration or impulse voltage to damage the insulation.

　　Liquid oil insulation fault liquid insulation of the oil-immersed transformer is 1887 by the American scientist Thomson invented, in 1892 by the United States General Electric Company to promote the use of power transformers, where the liquid insulation is the transformer oil insulation.

　　Oil-immersed transformer features: ① greatly improve the electrical insulation strength, shorten the insulation distance, reducing the size of the equipment; ② greatly improve the effective heat transfer and cooling effect of the transformer to improve the current allowable current density, Equipment weight, it is running the transformer body heat through the transformer oil thermal cycle, passed to the transformer shell and the radiator for heat, thereby improving the effective cooling and cooling level; ③ due to oil seal to reduce the internal transformer some Parts and components of the degree of oxidation, extending the service life.

　　1, the performance of transformer oil. In addition to the transformer oil in operation must have a stable and excellent insulation properties and thermal conductivity.

　　Which insulation strength tg8, viscosity, pour point and acid value is the main property of insulating oil indicators. The insulating oil prepared from petroleum is a mixture of hydrocarbons, resins, acids and other impurities, and their properties are not all stable and are continuously oxidized under the influence of temperature, electric field and photosynthesis. Under normal circumstances the oxidation process of the insulating oil is very slow, if the maintenance properly or even use 20 years can still maintain the quality and not aging, but mixed with oil in the metal, impurities, gas will accelerate the development of oxidation Quality deterioration, darker color, opacity, moisture, acid, ash, etc., so that the deterioration of the nature of the oil.

　　2, the reasons for the deterioration of transformer oil. Transformer oil quality deterioration, according to the severity can be divided into two stages of pollution and deterioration.

　　Pollution is the oil mixed with water and impurities, these are not the product of oil oxidation, pollution of the oil insulation performance will deteriorate, breakdown electric field strength decreases, the dielectric loss angle increases.

　　Deterioration is the result of oil oxidation, of course, this oxidation is not only pure oil in the oxidation of hydrocarbons, but the presence of impurities in the oil will accelerate the oxidation process, especially copper, iron, aluminum scrap.

　　Oxygen is derived from the air inside the transformer, and even if there is still about 0.25% oxygen in the fully sealed transformer, the oxygen has a higher solubility and therefore a higher ratio of the dissolved gas in the oil.

　　Transformer oil oxidation, as the catalyst of water and accelerator heat, so that the transformer oil to produce sludge, the main manifestations: the role of the electric field in the sediment particles; impurity precipitation concentrated in the strongest field, the transformer Insulation is formed as a conductive "bridge"; the precipitate is not uniform but forms a separate slender strip, and may be arranged in the direction of the power line, which undoubtedly hinders the heat dissipation, accelerates the aging of the insulating material and causes the insulation resistance to decrease and the insulation level The

　　3, the process of deterioration of transformer oil. The main stages of the process of oil in the process of degradation are peroxide, acid, alcohols, ketones and sludge.

　　Early stage of deterioration. The peroxide produced in the oil reacts with the insulating fiber material to produce oxidized cellulose, which makes the mechanical strength of the insulating fiber worse, resulting in embrittlement and insulation shrinkage. The resulting acid is a mucous fatty acid, although corrosive is not as strong as the mineral acid, but its growth rate and the impact on the organic insulation material is very large.

　　Late stage of deterioration. Is the formation of sludge, when the acid erosion of copper, iron, insulating paint and other materials, the reaction generated sludge, is a sticky and similar asphalt polymerization conductive material, it can be dissolved in the oil, the role of the electric field generated under the speed Soon, adhere to the edge of the insulating material or transformer shell, deposited in the tubing and cooler heat sink, etc., so that the transformer operating temperature, resistance to electrical strength decreased.

　　Oil oxidation process is composed of two main reaction conditions, one is the transformer acid value is too high, oil is acidic. The second is dissolved in oil oxide into oil-insoluble compounds, and thus gradually make the transformer oil quality deterioration.

　　4, transformer oil quality analysis, judgment and maintenance treatment.

　　① insulating oil deterioration. Including its physical and chemical properties are changed, so that its electrical properties deteriorate. By testing the acid value of the insulating oil, the interfacial tension, the precipitation of the Shantou, the water-soluble acid value and other items, it is possible to judge whether or not it belongs to the defect, and to regenerate the insulating oil, which may eliminate the product of oil deterioration. May have removed the natural antioxidant.

　　② insulating oil into the water damp, because the water is a strong polarity material. In the role of the electric field easily ionization decomposition, and increase the conductive oil of the conductive current, therefore, a trace of moisture can make a significant increase in dielectric oil dielectric loss. By testing the micro-water of the insulating oil, it is judged whether it belongs to such defects. Insulating oil pressure on the vacuum filter oil, the general can eliminate moisture.

　　③ Insulating oil is infected with microbial bacteria. For example, in the main transformer installation or hanging core, attached to the surface of the insulator insects and installers residual latch: stains and so may carry bacteria, which infected with insulating oil: or insulating oil itself has been infected with microorganisms. The main transformer - running in the 40-80 ℃ environment, is very conducive to the growth of these microorganisms, breeding. As the microbes and their excreta minerals, protein insulation performance is much lower than the insulating oil, making the dielectric oil dielectric loss increased. This defect is difficult to handle by means of on-site cycling, since no matter how it is handled, a portion of the microorganism remains on the insulating solids. After the treatment, the main transformer insulation will be restored in the short term, but because the main transformer running environment is very conducive to the growth and reproduction of microorganisms, these residual microorganisms will grow and multiply year by year, so that some of the main transformer insulation decreased year by year;

　　④ Alkyd resin insulating varnishes containing polar substances are dissolved in oil. In the role of the electric field, the polarity of the material will occur dipolar relaxation polarization, in the exchange of polarization process to consume energy, so the oil medium loss. Although the insulating paint in the factory before curing, but there may still be incomplete processing situation. After the main transformer is operated for a period of time, the insulating paint is not completely dissolved in the oil, so that the insulation performance gradually decreases. The time of occurrence of such defects is related to the degree of insulation treatment, and the effect can be achieved by one or two adsorption treatments.

　　⑤ oil only mixed with water and impurities. This pollution does not change the basic nature of the oil. For the water can be used to eliminate the dry way; for the impurities can be used to filter the way to clear; oil in the air can be excluded by a vacuum approach.

　　⑥ mixed with two or more different sources of insulation. The nature of the oil should be in accordance with the relevant provisions; the same proportion of oil, the same solidification temperature, the same viscosity, similar to the flash point; and the stability of the oil after mixing also meet the requirements. For the oil after the deterioration of oil, due to oil has changed, resulting in acidic substances and sludge, the need for oil regeneration of the chemical method to separate the product in order to restore its nature.

　　Dry-type resin transformer insulation and characteristics of dry-type transformers (here refers to the epoxy resin insulation transformer) is mainly used in places with high fire requirements. Such as high-rise buildings, airports, oil depots and so on.

　　1, the type of resin insulation. Epoxy tree refers to the insulation of the transformer according to the characteristics of the manufacturing process can be divided into epoxy quartz sand mixture vacuum casting type, epoxy alkali-free glass fiber reinforced vacuum pressure casting type and alkali-free glass fiber wrapping impregnated three.

　　① epoxy quartz sand mixture vacuum casting insulation. This type of transformer is a quartz sand as epoxy filler, will be impregnated with insulating paint wrapped around the coil, put the coil casting mold, under vacuum conditions and then mixed with epoxy resin and quartz sand drip irrigation pouring. As the casting process is difficult to meet the quality requirements, such as residual bubbles, the mixture of local uneven and may lead to local thermal stress cracking, so that the insulation of the transformer should not be used for hot and humid environment and load changes in the larger area.

　　② epoxy alkali-free glass fiber reinforced vacuum pressure casting insulation. Epoxy E-glass fiber reinforced with E-glass short fiber glass felt for the insulation of the outer layer of insulation insulation. The outer layer of the insulation package thickness is generally 1 ~ 3m of thin insulation, the proportion of epoxy resin castable mixture, and in high vacuum to remove the bubble casting, due to the thickness of the package insulation is thin, when the immersion It is easy to form a partial discharge point, so the need to mix the castable to complete, vacuum in addition to bubble to thoroughly, and master the watering