Classification of insulating materials

Gas insulating material

Generally, the dry gas under normal temperature and pressure has good insulation performance. As an insulating material, gas dielectric also needs to meet the requirements of physical, chemical properties and economy. Air and sulfur hexafluoride gas are common gas insulation materials.

Air has good insulation performance. After breakdown, its insulation performance can be restored instantly and automatically. It has stable electrical and physical properties, rich sources and wide application. However, the breakdown voltage of air is relatively low, sharp electrode, short distance, steep voltage waveform, high temperature, high humidity and other factors can reduce the breakdown voltage of air. Compressed air or vacuum pumping are often used to improve the breakdown voltage of air.

Sulfur hexafluoride (SF6) gas is a non combustible, non explosive, colorless and tasteless inert gas. It has good insulation performance and arc extinguishing ability, which is much higher than that of air. It has been widely used in high-voltage electrical appliances. Sulfur hexafluoride gas also has excellent thermal and chemical stability, but under the action of high temperature above 600 ℃, sulfur hexafluoride gas will decompose and produce toxic substances. Therefore, the following aspects should be paid attention to in use.

(1) Strictly control the water content and take dehumidification and moisture-proof measures.

(2) Use appropriate adsorbent to absorb harmful substances and moisture.

(3) The pressure of sulfur hexafluoride gas in the circuit breaker shall not be too high to cause liquefaction.

(4) The place where sulfur hexafluoride equipment is placed shall have good ventilation conditions.

(5) Necessary and reliable labor protection measures shall be taken for operation and maintenance personnel.

Liquid insulating material

Insulating oil includes natural mineral oil, natural vegetable oil and synthetic oil, as shown in the figure. Natural mineral oil is widely used. It is refined from crude oil to varying degrees

Electrical insulating oil is a neutral liquid, golden yellow, with good chemical and electrical stability. It is mainly used in power transformer, low oil circuit breaker, high voltage cable, oil immersed capacitor and other equipment. Natural vegetable oils include castor oil, soybean oil, etc. Synthetic oils include oxidized biphenyl methyl silicone oil and benzene methyl silicone oil. They are mainly used in power transformers, high-voltage cables and oil immersed paper capacitors.

Insulating oil will be affected by various factors during storage, transportation and operation, resulting in pollution and aging. Heat and oxygen play Zui major roles in oil aging. The measures taken to prevent oil aging in industry include: strengthening heat dissipation to reduce oil temperature; Isolate transformer oil from air with nitrogen and film; Use desiccant to eliminate moisture; Add antioxidants; Prevent sunlight, etc. After the oil is polluted, it can be purified and regenerated by pressure filtration or electric purification.

In order to ensure the safe operation of oil filled equipment, the oil temperature rise, oil level height, oil flash point, acid value, breakdown strength and dielectric loss tangent must be checked frequently, and the chromatographic analysis of transformer oil must be carried out if necessary. When it is necessary to supplement oil, the original model or similar model shall be used as far as possible, and the mixing test shall be carried out.

Solid insulating material

There are many kinds of solid insulating materials, which have excellent insulation performance and are widely used in power system. The commonly used solid insulating materials are: insulating paint and insulating glue; Fiber products; Rubber, plastics and their products; Glass and ceramic products; Mica, asbestos and its products.

Insulating paint and insulating glue are important insulating materials based on high polymer and can be solidified into insulating hard film or insulating whole under certain conditions.

The insulating paint is mainly composed of paint base, solvent, diluent, filler, etc. the insulating paint has high insulation strength after film-forming and curing, and can generally be used as impregnation insulation or coating insulation of motor and electrical coil. It can be divided into impregnation paint, enamelled wire paint, covering paint, silicon steel sheet paint and anti corona paint according to its application.

Insulating glue is similar to insulating paint, generally with filler. It is widely used for pouring cable joints, bushings, current transformers of 220kV and below, and voltage transformers of 10kV and below. The insulation glue used includes yellow cable glue, black cable glue, epoxy cable glue, epoxy resin glue, epoxy polyester glue, etc.

Insulating fiber products refer to insulating materials made of insulating paper, paperboard, paper tube and various fiber fabrics. Impregnated fiber products are made of insulating fiber products as substrate and impregnated with insulating paint. It has certain mechanical strength, electrical strength and moisture resistance. It also has some special functions such as mildew prevention, electricity prevention and radiation prevention. Insulating electrical laminated products are layered insulating materials made of fiber as substrate, impregnated with different adhesives, hot pressed or rolled. Their properties depend on the substrate, adhesive and its forming process. They can be made into products with excellent electrical properties, mechanical properties, heat resistance, mold resistance, arc resistance, corona resistance and other characteristics.