For the purpose of electrical insulation of conductors, electrical insulating materials, dielectrics, are used. These materials have extremely low conductivity and high electrical strength, so they are well suited for this kind of application.
There are organic and inorganic electrical insulating materials. Organic, unlike inorganic, contain carbon. As for inorganic dielectrics, they have better temperature characteristics. According to the method of their production, electrical insulating materials are natural (natural) and synthetic.
Synthetic materials are often preferred because, thanks to the vast possibilities of the modern chemical industry, there are opportunities to create materials that precisely meet the requirements placed on them.
It should be noted that dielectrics are divided into polar and non-polar. Non-polar molecules are electrically neutral. A striking example of a non-polar dielectric is polyethylene. Within this group, ionic crystalline materials stand out, such as mica or quartz, where pairs of ions form electrically neutral particles. Molecules of polar dielectrics by nature have a non-zero electric dipole moment, such materials have a higher dielectric constant. A striking example of such a material is polyvinyl chloride.
In addition, dielectrics differ in their state of aggregation. They can be liquid, solid or gaseous. Gaseous are natural gases: air, nitrogen, carbon dioxide, helium, neon, argon, krypton. They are rarely used as insulators. Liquid ones are a little more practical (in demand in transformers, switches, cables, bushings). However, petroleum oils and synthetic formulations are often flammable or toxic. Solid - the most in demand and very widely applicable. Less often - natural: amber, shellac. More often - synthetic: epoxy resins, polyimides, silk, ethylcellulose, etc. Laminated plastics, varnishes and plastics are also widely used in the production of dielectric parts.
In recent years, a large number of polymeric materials have been obtained and are being produced, which are in demand in a large number of fields of technology due to their dielectric properties, which make it possible to use many of these materials as insulating materials. Amorphous and crystalline polymers are capable of forming densely packed ordered structures. Amorphous forms are isotropic, that is, their properties are the same in all directions. They are usually transparent, chemically resistant, wear-resistant. The crystalline phase has more pronounced qualities of stability, however, it is characterized by anisotropy, that is, the properties depend on the direction in the crystal structure.
The most promising direction in the development of electrical insulating materials today is the topic of polymer composites. Most recently, in 2021, specialists from the Central Research Institute of KM "Prometey" (NRC "Kurchatov Institute") obtained significant results in the development of electrical insulating products from polymer composites based on an epoxy matrix reinforced by winding with glass, carbon, and organoplastics. The technology will make it possible to create large-scale thick-walled products with high electrical strength, such as: insulating elements of stator windings of turbogenerators, transformer coils and insulating cylinders for surge arresters.
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