Insulation material for oil-immersed transformers

Oil-immersed transformer is a kind of transformer that uses insulating oil as cooling and insulating medium. Its working principle is to convert AC electrical energy of one voltage level into another voltage level of the same frequency‌. The core components of an oil-immersed transformer include an iron core made of a material with good magnetic conductivity and a winding impregnated in insulating oil. The insulating oil not only acts as insulation, but also helps the transformer to maintain stable operation under high load conditions through its high heat capacity characteristics.

Insulation material for oil-immersed transformers

1. Transformer oil: As the main insulating medium of oil-immersed transformers, transformer oil not only has good insulation performance, but also can effectively transfer the heat generated inside the transformer to the external environment to play a cooling role.

2. Insulating paper: Insulating paper has good heat resistance and electrical properties in the internal environment of the transformer. It is often used to make insulating gaskets and insulating bushings and other parts. In addition, insulating paper also includes cable paper, crepe paper and so on. Cable paper is made of sulfate pulp, which is mainly used for insulating the outer surface of wire and insulation between coil layers. Crepe paper is made of cable paper reprocessing. Its electrical properties in the oil performance is excellent and mainly used as a transformer wire binding material.

·‌DDP is a kind of insulating material which is coated with modified special epoxy insulating resin in diamond pattern on electrical insulating paper. ‌This material is non-adhesive and dry at room temperature (below 35℃), and has excellent insulation properties and stability. ‌DDP is widely used in high-voltage equipment such as transformers and motors, which can effectively prevent the occurrence of breakdown and insulation failure.‌

·Cable paper, also known as insulation paper. It is a special paper material made of cellulose fiber and is used for the insulation layer and outer protective layer of wire and cable. Cable paper has unique insulation properties. It can withstand high temperature, high voltage and mechanical stress, so as to protect the normal operation of the cable line and extend the service life of the cable.

·Crepe paper ‌is an insulating material made by a special crepe process and is usually made of 100% pure imported pulp. This material has high electrical and mechanical properties. So it is widely used in the insulation protection of power equipment and electronic devices.

·Phenolic paper tubes are engineered composite materials constructed from multiple layers of paper, typically kraft paper, which is renowned for its high tensile strength and durability. The kraft paper serves as the foundational base material, while phenolic resin acts as a powerful binding agent. It has remarkable resistance to heat, chemicals and wear and can penetrates the paper fibers to create a cohesive and unified structure. Phenolic paper tubes are often used as insulating structural parts in motors and electrical equipment and are used for insulation isolation between coils.

3. Insulating film: Such as polyimide film, polyethylene film, etc., these film materials are often used to wrap insulating paper and insulating enameled wire to further enhance the insulation performance.

·Polyimide Film is the best filmic insulation material in the world, it consists of Pyromellitic dianhydride (PMDA) and diamino-diphenyl ether(DDE) in strong polar solvents by condensation and re-cast film made by the imidization. Being named as “Golden Film”, polyimide film with excellent performance, such as high temperature and low temperature capabilities, electrical insulating properties, cohesiveness, radiation resistance, media resistance, good chemical stability and self-extinguishing etc. In addition, its surface (side) has a unique roughening process, which can improve product composite bonding capacity.

4. Insulated enamelled wire: This material provides additional insulation protection by wrapping the wire in an insulating coating. Common insulating coating materials include polyimide and so on.

5. Insulation tape: Such as linen tape, insulating rubber tape, etc., these tape materials are also used to wrap insulating paper and insulating enameled wire to increase insulation strength.

Oil-immersed transformer is an important equipment in power system, its insulation material selection and performance requirements are very important. These insulating materials can not only withstand extreme conditions such as high voltage and high temperature during transformer operation, but also have good electrical properties, mechanical strength and chemical stability.