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All about the transformer insulation material

  Insulation material is one of the most important materials in the transformer, its performance and quality directly affect the reliability of transformer operation and transformer life. In recent years, the transformer products used in new insulation materials after another.

  First, the transformer insulation material overview

  With the rapid development of science and technology, electrical appliances, transformers and other electrical equipment is increasingly widely used. The reliability and service life of the transformer is largely dependent on the insulation material it uses. Insulation materials are increasingly engaged in the design and manufacture of transformers.

  Over the past two decades, transformers insulation materials aspects of new products, new technologies, new theories continue to emerge and development, so that the transformer insulation materials and its application has formed a very important discipline.

  1. Introduction to Insulation Materials

  Insulation material, also known as dielectric, is a high resistivity, low conductivity of the material. Insulation material can be used to isolate live or different potential of the conductor, so that the current flow in a certain direction. In the transformer products, insulation materials also play a cooling, cooling, support, fixed, arc, improve the potential gradient, moisture, mildew and protect the role of the conductor.

  (105 ≧), B (130 ≧), F (155 ≧), H (180 ≧), C (greater than 180), the temperature of the insulation materials are classified according to the voltage grade: C).

  Transformer insulation material heat resistance grade refers to the insulation material in the transformer to allow the maximum temperature. If the correct use of insulating materials, you can guarantee the material 20 years of service life. Otherwise it will be based on 8 ≧ law (A-class insulation temperature for each 8 ≧ rise, half life cycle, B-class insulation is 10 ≧, H level is 12 ≧. This law is known as heat aging 8 ≧ law) Service life. The heat resistance of the insulating material composed of the polymer is lower than that of the inorganic dielectric. The properties of insulating materials are closely related to their molecular composition and molecular structure.

  Transformer insulation materials a lot of varieties, according to their form can be divided into gas insulation materials, liquid insulation materials and solid insulation materials.

  2, transformer insulation material electrical performance of the four basic parameters.

  The four basic parameters of the electrical properties of transformer insulation include insulation resistance, dielectric coefficient, dielectric loss factor and dielectric strength.

  Insulation resistance

  1. The concept of insulation resistance Insulation material resistance refers to the insulation material in the role of DC voltage, the pressure is longer, and the line on the charging current and absorption current disappears, only the leakage current through the resistance value / general provisions After adding a voltage for one minute, the measured resistance value is the insulation resistance value. For high-voltage large-capacity transformers, the insulation resistance is specified for 10 minutes.

  2. Factors that affect the insulation resistance

  3. The relationship between temperature and insulation resistance

  With the increase of temperature, the resistivity decreases exponentially, because when the temperature increases, the molecular thermal motion increases, the average kinetic energy of the molecule increases, the molecular kinetic energy can reach the activation energy, the ion is easy to transfer.

  4. The relationship between moisture and insulation resistance

  Moisture immersion in the dielectric, an increase of conductive ions, but also to promote the dissociation of impurities and polar molecules. So the insulation material decreases as the humidity increases, especially the insulation paper or insulating paperboard insulation resistance decreases more.

  The moisture content of the dielectric surface of the dielectric surface is very sensitive to the surface resistance of the ion crystal, and the hydrophobic material of the ionic crystal is more attractive to the water than the cohesion of the water molecules. The continuous water layer on the surface reduces the surface resistance. So electrical equipment due to moisture caused by reduced insulation resistance, resulting in leakage current is too large and damage the equipment.

  5. It is also easy to mix into polar materials, and promote the dissociation of polar molecules to make conductive ions more.

  The surface of the dielectric is contaminated by impurities, and the adsorption of water will cause the surface resistivity to drop rapidly. Insulation resistance of the insulating material is one of the most sensitive parameters reflecting the amount of impurities in the material. In order to ensure the insulation level of the insulating material, the insulating material plant must strictly control the cleanliness of the production environment in the standard of insulating material. The method of measuring the volume resistivity of the insulating material is often used to measure the impurity content of the insulating material.

  6. The relationship between the electric field strength and the insulation resistance

  In the case of the electric field strength is not too high, the electric field strength on the ion transfer capacity and the impact on the resistivity is very small. When the electric field strength increases, the ion migration ability increases with the electric field intensity, so that the resistivity decreases, when the electric field strength increases to the dielectric near breakdown, due to a large number of electrons migration, the resistivity index exponentially.

  Dielectric loss

  1. Dielectric loss

  In the AC voltage, the dielectric part of the power will be converted into heat, this part of the energy called the dielectric loss, which is mainly caused by the conductive and slow relaxation polarization, it is also leading to dielectric breakdown of the root causes. Often the energy consumed per unit of time is called the dielectric loss power

  2. The form of dielectric loss

  Divided into: free loss, dipole loss, conductance loss, uneven dielectric loss

  Insulation aging

  1. The concept of insulation aging

  In the course of electrical equipment operation due to long-term by various factors, the insulation material occurs a series of irreversible chemical and physical changes, resulting in electrical and mechanical properties of the deterioration, this irreversible change is often referred to as aging. Insulation aging is divided into heat aging, environmental aging and electrical aging. Factors that cause aging are heat, electricity, light, oxygen, radiation and microbes.

  Five. Heat aging

  Due to the heat, the aging of the insulating material is called heat aging. In the heat aging process, the polymer insulation material often occurs thermal degradation, low molecular weight generation or escape. So that the insulation properties of insulating materials and mechanical properties decreased.

  Electrical aging

  In electrical equipment, the insulating material in the role of the electric field, the performance of irreversible changes until the failure, the process known as electrical aging. The main reason for the aging of insulating materials is partial discharge. As the partial discharge of ozone, ozone is a strong oxidant, so that the double bond with the macromolecules from the reaction, the material ozone cracking.

  7. Aging of the environment

  Environmental aging refers to the insulating material in the light, oxygen, radiation and acid and other factors caused by the pollution of chemical reactions, in which the sun is the main factor in ultraviolet light.

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