Classification of Insulating Material

Insulating materials are non-conductive materials under allowable voltage, but not absolutely non-conductive materials. Under the action of certain external electric field strength, conduction, polarization, loss, breakdown and other processes will occur, and aging will occur in long-term use. Its resistivity is very high, usually in the range of 1010-1022Ω·m. For example, in the motor, the insulation material around the conductor separates the turns from the grounded stator core to ensure the safe operation of the motor. Today, we will introduce the classification of insulation materials.

Gas Insulating Materials

Usually, dry gases at room temperature and pressure have good insulation properties. Gas dielectrics, as insulating materials, also need to meet the physical, chemical and economic requirements. Air and sulfur hexafluoride are commonly used gas insulating materials.

Air has good insulation performance. After breakdown, its insulation performance can be restored instantaneously and automatically. Its electrical physical performance is stable, its source is very rich, and its application is wide. However, the breakdown voltage of air is relatively low, such as sharp electrodes, close distance, steep voltage waveform, high temperature, high humidity and other factors, which can reduce the breakdown voltage of air. Compressed air or vacuum pumping are often used to improve the breakdown voltage of air.

Liquid Insulating Materials

Insulating oils are natural mineral oil, natural vegetable oil and synthetic oil, as shown in the figure. Natural mineral oil is widely used. It is a neutral liquid obtained from petroleum crude oil after refining to varying degrees. It is golden yellow and has good chemical and electrical stability. Mainly used in power transformers, oil-less circuit breakers, high-voltage cables, oil-immersed capacitors and other equipment. Natural vegetable oils include castor oil, soybean oil, etc. Synthetic oils include oxidized biphenyl methyl silicone oil and benzyl methyl silicone oil. They are mainly used in power transformers, high voltage cables and oil-impregnated paper dielectric capacitors.

Insulating oil will be polluted and aged by various factors during storage, transportation and operation. Heat and oxygen play the most important roles in oil aging. The anti-oil aging measures adopted in industry include: strengthening heat dissipation to reduce oil temperature; isolating transformer oil from air by nitrogen and film; using desiccant to remove moisture; adding antioxidant; preventing sunlight exposure, etc. After oil is polluted, it can be purified and regenerated by pressure filtration or electric purification.

In order to ensure the safe operation of oil-filling equipment, it is necessary to check the temperature rise of oil, oil surface height, oil flash point, acid value, breakdown strength and tangent value of medium loss angle, and to carry out chromatographic analysis of transformer oil when necessary. When you need to add oil, try to use prototype number or similar model, and mixing test should be carried out.

Solid Insulating Materials

There are many kinds of solid insulating materials, which have excellent insulation performance and are widely used in power system. Commonly used solid insulating materials are: insulating paint, insulating glue, rubber, plastics, glass, ceramic products, mica, asbestos.

Insulation coatings and adhesives are important insulating materials based on macromolecule polymers, which can be solidified into insulating hard films or whole insulating materials under certain conditions.

Insulating paint is mainly composed of paint base, solvent, diluent, filler and so on. The film-forming and solidification of insulating paint have higher insulation strength. It can generally be used as impregnating insulation or coating insulation for motor and electrical coils. According to its use, it can be divided into impregnating paint, enameled wire paint, covering paint, silicon steel sheet paint and corona-proof paint.

Insulating glue is similar to insulating paint. It is usually filled with fillers. It is widely used for casting cable joints, bushing, 220 kV current transformer and 10 kV voltage transformer. The insulating adhesives used are yellow cable adhesives, black cable adhesives, epoxy cable adhesives, epoxy resin adhesives, epoxy polyester adhesives, etc.

Insulating fiber products refer to insulating materials made of insulating paper, cardboard, paper tubes and various fiber fabrics. Impregnated fiber products are made of insulating fiber products as substrates and insulating paint. It has certain mechanical strength, electrical strength, moisture resistance, and also has some special functions such as mildew, electricity and radiation protection. The laminated insulating material of insulating layer is made of fibers as substrates, dipped with different adhesives, hot pressed or rolled. Its properties depend on the substrates and adhesives and their forming process. It can be made into products with excellent electrical properties, mechanical properties, heat resistance, mildew resistance, arc resistance and corona resistance.

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