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Performance and Application of Transformer Paper Insulation

  Insulation system composed of transformer insulation is the basic conditions for the normal operation and operation of the transformer. The service life of the transformer is determined by the life of the insulating material. The aging of the transformer insulation is that the material is decomposed by environmental factors, Lost the insulation strength. According to statistics, due to various types of insulation failure occurred in the accident accounted for more than 85% of all transformer accidents. Practice has proved that most of the transformer damage and damage to the insulation system. As the paper insulation material is an important part of the transformer insulation system, it is also one of the main causes of transformer accidents.

  1, the characteristics of paper insulation materials

  Paper insulation is one of the main insulating materials of oil-immersed transformers, including: insulating 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 is about 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. When the temperature is raised, the degree of cyclization of the cellulose, the chain breakage and the degree of gas generation are different. At a certain temperature, CO and CO2 production rate is constant, that is, the oil CO and C02 gas content with a linear relationship with time. When the temperature is rising, the production rate of CO and CO2 tends to increase exponentially. Therefore, the content of CO and CO2 in the oil has a direct relationship with the thermal aging of the insulating paper, and can change the content as one of the criteria for the abnormality of the paper in the sealed transformer. And solid insulation has irreversible aging properties, its mechanical and electrical strength reduction can not be restored. As the power transformer in the run to withstand the intermittent mechanical stress, tension, pressure, torque and atmospheric over-voltage and internal over-voltage impact, the insulation material requirements are high. Therefore, according to the characteristics of paper insulation materials, to enhance the oil-immersed transformer operation control and maintenance.

  2, the performance of paper insulation 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. It is believed that the paper is sealed, it can reduce the absorption of water on the paper to prevent oxidation of materials, can achieve better results. But in practice when the polar substance containing alkyd resin varnish dissolved in the 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. But may also be some paint will slowly dissolve into the oil, affecting the performance of oil, the application of such paint should be given full attention.

  3, the mechanical strength of paper insulation material

  Oil-immersed transformers Select the most important factor in paper insulation. In addition to the fiber composition, density, permeability and uniformity of paper, it also includes mechanical strength requirements, usually characterized by tensile strength, stamping strength, tear strength and toughness The To determine the insulation properties of paper 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 aging of solid insulation. Paper fiber insulation materials in the operation and maintenance, should pay attention to control the transformer rated load, requiring the operation of the environment air circulation, heat dissipation conditions, to prevent the transformer temperature rise exceeded. This is based on the oil-immersed transformer in the rated load, the winding average temperature rise of 65 ≧, the hottest temperature rise to 78 ≧, if the average ambient temperature of 20C, the hottest temperature of 98 ≧; at this temperature, the transformer can run 20 - 30 years, if the transformer overload operation, the temperature increases, to promote life shortened. International Electrotechnical Commission (1EC) that the A-class insulation transformer in the 80 ~ 140C temperature range, the temperature increase of 6 ≧, the transformer insulation effective life will reduce the speed of doubling, which is 6 ≧ law, that the heat limit Has been more stringent than the previously recognized 8 ° C law. At the same time, please visit: transmission and distribution equipment network also to prevent oil pollution, deterioration caused by accelerated aging of the fiber, and damage the transformer insulation performance, service life and safe operation.

  4, the deterioration of paper fiber material

  Paper fiber degradation mainly includes three aspects: one, 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. Second, the mechanical strength of the fiber material decreased. The mechanical strength of the fibrous material decreases with the prolongation of the heating time. When the insulation of the insulating material causes the moisture of the insulating material to be discharged again, the value of the insulation resistance may be high, but the mechanical strength will be greatly reduced, and the insulating paper will not resist the short circuit Current or impact load and other mechanical forces. Third, the information please visit: lose fiber material itself shrink. 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.

  5, paper insulation material equipment operation and maintenance

  In summary, master the power transformer paper insulation material performance and reasonable operation and maintenance of the transformer, a direct impact on the safe operation of the transformer, life and power supply reliability, and preventive and predictive maintenance is to improve the transformer life and The key to improving the safe operation level. Power transformers are important and key main equipment in power systems. As the operation and maintenance personnel and managers of transformers, it is necessary to understand and master the insulation structure, material properties, process quality, maintenance methods and scientific diagnostic techniques of power transformers and optimize them. Operation and management, to strengthen the transformer insulation system reasonable maintenance, in order to ensure the use of power transformers efficiency, life and power supply reliability.

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