The operational reliability and service life of a transformer, however, depend to a large extent on the insulating materials used. Insulating materials, also known as dielectrics, are substances with high resistivity and low conductivity. Insulating materials can be used to isolate conductors that are charged or at different potentials and allow current to flow in a certain direction. In transformer products, insulating materials also play the roles of heat dissipation, cooling, support, fixation, arc extinguishing, improving potential gradient, moisture-proof, mildew-proof and protecting conductors.
Typically, insulation materials are divided into three categories:
1) Gas insulation materials: Under normal temperatures and pressures, general dry gases have good insulation properties, such as air, nitrogen, hydrogen, carbon dioxide, sulfur hexafluoride, etc. Among them, air and sulfur hexafluoride are used in transformers. widely;
2) Liquid insulation material: Liquid insulation material usually exists in the form of oil, also known as insulating oil. Such as mineral oil, vegetable oil, synthetic ester, etc.;
3) Solid insulating materials: such as insulating paint, insulating glue, insulating paper, insulating cardboard, corrugated cardboard, electrical plastics and films, electrical laminates (rods, tubes), cast epoxy resin, electrical porcelain, rubber, mica products, etc.
Ⅰ Insulating oil
Insulating oil is characterized by high electrical strength, high lightning, low freezing point, high performance under the action of oxygen, high temperature, and strong electric field, non-toxic, non-corrosive, low viscosity, and good fluidity. It is widely used in electrical products such as transformers, oil switches, capacitors and cables. It plays the role of insulation, cooling, impregnation and filling. In addition, it also plays the role of arc extinguishing in oil switches and energy storage in capacitors.
Insulating oil plays the dual roles of insulation and cooling in transformers;
Insulating oils are currently generally divided into the following categories:
1) Mineral oil: such as transformer oil, switch oil, capacitor oil, cable oil;
2) Synthetic oil: such as dodecylbenzene, silicone oil, synthetic ester, etc.;
3) Vegetable oil;
Ⅱ Epoxy resin
