Heat-insulating materials

General information

Insulating materials (electrical insulating materials) are insulators that serve for electrical insulation. Actually, electrical insulating materials are designed to prevent the flow of direct and/or alternating current.

Electrical insulating materials are used in electrical, radio engineering and electronic devices and appliances.

High volume resistivity, high breakdown potential, low dielectric loss tangent and low dielectric constant are desirable for electrical insulating materials. It is important that the above parameters are stable in time and temperature, and sometimes also in the frequency of the electric field.

Electrical insulating materials can be distinguished:

by aggregative state:

· Gaseous

· Liquid

· Solid

by origin:

· Natural inorganic

· Artificial inorganic

· Natural organic

· Synthetic organic

Gaseous. All gaseous electrical insulating materials have a dielectric constant close to 1 and dielectric loss tangent is also small, but the breakdown potential is also low. Air is most often used as a gaseous insulator, but recently SF6 (sulfur hexafluoride, SF6) has been used more often, which has almost three times the breakdown potential and significantly higher than arc suppression capacity. Sometimes a combination of gaseous and organic materials is used to make electrical insulating materials.

Liquid — most commonly used in transformers, switches, cables, bushings for electrical insulation, and capacitors. Moreover, these dielectrics are also serve as cooling liquids in transformers, and an arc-extinguishing medium in switches. Transformer oil, capacitor oil, castor oil, synthetic fluids are primarily used as liquid dielectric materials.

Natural inorganic — the most common material is mica; it is flexible while maintaining strength; it breaks down well, which makes it possible to obtain thin plates. Chemically and heat resistant. Muscovite mica and phlogopite are used as electrical insulating materials, however, muscovite mica is better.

Artificial inorganic: Low-alkali glass, fiberglass, and ceramic glass have good insulation resistance, but the main electrical insulating material is still porcelain (feldspar ceramics). This ceramics is widely used for high voltage current-carrying wire insulators, bushing insulators, bushings, etc. However, due to high dielectric loss tangent, it is not suited for high frequency insulators. Forsterite, alumina, cordierite, and other ceramics are used for other more specific tasks.

Natural organic: Recently, due to the expansion of production of synthetic electrical insulating materials, their use has been decreased. The following can be singled out – cellulose, paraffin, pitch, rubber, amber and other natural resins; liquid ones include castor oil.

Synthetic organic: The share of high-molecular chemical compounds – plastics and elastomers – is the most. There are also synthetic dielectric fluids.