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Solid paper insulation fault

  Solid paper insulation is one of the main parts of oil-immersed transformer insulation, including: insulating paper, insulation board, insulation pad, insulation roll, insulation banding, etc. The main component is cellulose, chemical expression (C6H10O6) n, 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:

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

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

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

  ∠ 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: 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.

   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.

   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.

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