Insulation material: jué yuán cái liào
Materials used in electrical equipment to insulate live parts from other parts. Commonly used solid materials include insulating paper, leather, rubber, plastic, paint, glass, ceramic, mica, etc. Commonly used liquid materials include transformer oil, etc. Among gaseous materials, air, nitrogen, sulfur hexafluoride, etc. are the most commonly used.
Insulating material: Materials made of substances with a resistivity of 109 to 1022 Ω·Cm are called insulating materials in electrical technology, also called electrolytes. Simply put, it is a material that insulates charged bodies from other parts. Insulating materials have a very high resistance to direct current. Under the action of direct voltage, except for a very small surface leakage current, they are actually almostnon-conductive. For alternating current, capacitive current passes through, but it is also considered to be. non-conductive. The higher the resistivity of the insulating material, the better the insulation performance.
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Insulating material
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Material used to insulate conductive parts from different potentials. Its electrical conductivity is approximately less than 10-10 W/meter. In different electrical products, according to needs, insulating materials often also play the roles of energy storage, heat dissipation, cooling, arc extinguishing, moisture resistance, mildew resistance, corrosion, radiation, mechanical support and fixation, and conductor protection.
Classification and performance There are many types of insulating materials, which can be divided into three categories: gazy, liquid and solid. Commonly used gas insulation materials include air, nitrogen, sulfur hexafluoride, etc. Liquid insulation materials mainly include mineral insulating oil and synthetic insulating oil (silicone oil, dodecylbenzene, polyisobutylene, isopropylbiphenyl, diarylethane, etc.). Solid insulating materials can be divided into two categories: organic and inorganic. Organic solid insulation materials include insulating paint, insulating glue, insulating paper, insulating fiber products, plastics, rubber, varnish paint pipes and insulating impregnated fiber products, electrical films, composite products and adhesive tapes, electrical laminates, etc. Inorganic solid insulating materials mainly include mica, glass, ceramics and their products. On the other hand, solid insulation materials are diversers and very important.
Different electrical equipment has different requirements for the performance of insulating materials. Insulating materials used in high-voltage electrical equipment such as high-voltage motors and high-voltage cables require high breakdown resistance and low dielectric loss. Low-voltage electrical devices have the main requirements of mechanical strength, elongation at break, heat resistance level, etc.
The macroscopic properties of insulating materials, such as electrical properties, thermal properties, mechanical properties, chemical resistance, climate change resistance, corrosion resistance and other properties are closely linked to its chemical composition and molecular structure. Inorganic solid insulating materials are mainly composed of silicon, boron and various oxidesmetallic. They are mainly ionic structures. Their main characteristics are high heat resistance, operating temperature generally above 180°C, good stability, resistance to atmospheric aging. has good chemical resistance and long-term aging performance under the action of electric field; but it has high brittleness, low impact resistance, high pressure resistance, low tensile strength and poor processability; organic materialThe material is generally a polymer with an average molecular weight between 104 and 106, and its heat resistance is generally lower than that of inorganic materials. The thermal resistance of materials containing aromatic rings, heterocyclic rings, silicon, titanium, fluorine and other elements is higher than that of high-temperature polymer materials.general linear system.
Important factors that affect the dielectric properties of insulating materials are the strength of molecular polarity and the content of polar components. The dielectric constant and dielectric loss of polar materials are higher than those of nonpolar materials, and they easily absorb impurity ions to increase conductance and reduce their dielectric properties. Therefore, precautions must be taken during the manufacturing process of insulating materials to avoid contamination. The dielectric used in capacitors requires a high dielectric constant to improve its specific characteristics.
Development Overview The first insulating materials used were natural products such as cotton, silk, mica and rubber. At the beginning of the 20th century, industrial synthetic plastic phenolic resin first appeared, which has good electrical properties and high heat resistance. Later, urea-formaldehyde resin and alkyd resin with better performance appeared one after another. The emergence of synthetic trichlorobiphenyl insulating oil provided a quantum leap in the specific characteristics of power capacitors (but its use has since been abandoned as harmful to human health). Sulfur hexafluoride was also synthesized during the same period.
Since the 1930s, synthetic insulation materials have developed rapidly, including acetal resin, chloroprene rubber, polyvinyl chloride, styrene-butadiene rubber, polyamide, melamine, polyethylene and the excellent performance of Plastic King's PTFE, etc. The emergence of these synthetic materials has played a major role in the development of electrical technology. For example, enameled wire in acetal is used in motors to increase operating temperature and reliability, while the size and weight of the motor are significantly reduced. The successful development of fiberglass and its braided tape as well as the synthesis of silicone resin have added Class H thermal resistance to the motor insulation.
Unsaturated polyester and epoxy resins appeared after the 1940s. The emergence of pink mica paper freed people from the dilemma of lack of mica resources.
Since the 1950s, new synthetic resin materials have been widely used. Insulating glues such as unsaturated polyester and epoxy can be used to impregnate high voltage motor coils. Polyester series products are used in motor slot lining insulation, enameled wires and impregnated varnishes, and have developed class low-voltage motor insulationE and Class B, further reducing engine size and weight. Sulfur hexafluoride began to be used in high-voltage electrical devices, allowing them to be transformed into high-capacity and miniaturized products. The air insulation of circuit breakers and the oil and paper insulation of transformers are partially replaced by sulfur hexafluoride.
In the 1960s, heat-resistant resins containing heterocyclic and aromatic rings were greatly developed, such as polyimide, polyaramid, polyarylsulfone, polyphenylene sulfide, etc., which are H grade and higher thermal quality. materials. The synthesis of these heat-resistant materials creates favorable conditions for the future development of class F and H motors. Polypropylene films were also successfully used in power capacitors during this period.
Since the 1970s, there has been relatively little development and research into new materials. During this period, emphasis was placed on various modifications of existing materials and on expanding their scope of application. A new method is used to refine mineral insulating oil to reduce its losses; epoxy mica insulation improves its mechanical properties and gets no air gap to improve its electrical properties.Many performance improvements have been made. Power capacitors have evolved from paper-film composite structures to full-film structures. Research has begun to replace traditional natural fiber paper with synthetic insulation paper for 1,000 kilovolt ultra-high voltage electrical cables. Non-polluting insulation materials have also developed rapidly since the 1970s, as the replacementt chlorinated biphenyl, a toxic medium, with cumene and ester oil, a non-toxic medium, and the expanded application of solvent-free paint. With the popularity of household appliances, major fires frequently occur due to fires caused by insulating materials. Therefore, research on flame retardant materials has attracted attention.
Development trends The level of research and development of insulating materials is one of the keys affecting and limiting the development of electrical technology. Judging from future trends, it is necessary to develop high voltage and heat resistant insulators, solvent-free and pollution-free insulators, composite insulators resistant to corrosion, water, oil, cryogenics, radiation. resistant and flame-retardant materials, and the development of energy-efficient materials. Emphasis is placed on the development of IS systemsepoxy mica olation for high voltage and large capacity generators; class F and H insulation series for small and medium-sized motors; sulfur hexafluoride gas carriers for high-voltage power transmission and transformation equipment; new types of chlorinated biphenyl substitutes Non-toxic synthetic media; high performance insulating oil; flame retardant synthetic paper composite insulation and surface protection materials, etc. At the same time, we must actively accelerate the insulation upgrade. materials for traditional electrical equipment.