What are the main insulating materials used for transformers?

Insulating materials are one of the most important materials in transformers, and their performance and quality directly affect the reliability of transformer operation and the service life of transformers. In recent years, new insulating materials have been emerging one after another in transformer products. With the rapid development of science and technology, the application of electrical equipment such as motors and transformers is becoming increasingly widespread. The reliability and service life of a transformer's operation largely depend on the insulating materials it uses. Insulating materials are increasingly valued by those engaged in the design and manufacture of transformers. Over the past two decades, new products, technologies and theories in the field of transformer insulation materials have been constantly emerging and developing, thus making transformer insulation materials and their applications a very important discipline.

Insulating materials, also known as dielectrics, are materials with high resistivity and low electrical conductivity. Insulating materials can be used to isolate conductors that are charged or at different potentials, allowing the current to flow in a certain direction. In transformer products, insulating materials also play a role in heat dissipation, cooling, support, fixation, arc extinguishing, improving potential gradient, moisture-proofing, mold-proofing and protecting conductors, etc. Insulating materials are classified by voltage level: generally, they are divided into: Y (90℃), A (105 ℃), E (120℃), B (130℃), F (155℃), H (180℃), and C (above 180℃). The heat resistance grade of transformer insulation materials refers to the maximum temperature that the insulation materials are allowed to withstand in the transformer. If insulating materials are used correctly, a 20-year service life of the materials can be guaranteed. Otherwise, the 8℃ rule will be applied (for every 8℃ increase in the temperature of Class A insulation, the service life is halved; for Class B insulation, it is 10℃; and for Class H insulation, it is 12℃). This rule, known as the 8℃ rule of thermal aging, reduces the service life. The heat resistance of insulating materials composed of polymers is half lower than that of inorganic dielectrics.

The properties of insulating materials are closely related to their molecular composition and molecular structure. There are many types of transformer insulating materials. Generally, they can be classified into gas insulating materials, liquid insulating materials and solid insulating materials according to their forms.

Solid insulating materials: The solid insulating materials used in transformers refer to those that are solid in their own form or have undergone chemical reactions or physical changes to become solid. There are various types of solid insulating materials for transformers, such as insulating paper, insulating cardboard, Nomex paper, glued paper, electrical laminated wood, epoxy glass cloth board, low dielectric loss laminated board, insulating varnish, insulating glue, cotton cloth tape, compression tape, mesh non-weft polyester tape, etc.

01 Insulating paper

The insulating paper mentioned here refers to pure sulfate wood pulp paper. Other insulating papers include synthetic fiber paper (such as NOMEX paper), nitrile insulating paper (such as Denison paper), and so on.

02 Insulating crepe paper

It is made by creasing insulating paper used by electricians. There are wrinkles along its transverse direction, and the wrinkles are pulled apart when stretched. Due to different wrinkling processing procedures, crepe paper with different elongation rates can be made. The thickness of insulating paper is generally 0.05mm to 0.12mm, and the elongation range is 5% to 200%. Insulating crepe paper is often used for winding insulation in oil-immersed transformers, such as winding protruding.

03 Denison paper

This insulating paper is called nitrile paper. During its manufacturing process, dinitrile amine, vinyl cyanide and other substances are added to the pulp. Produced by Denison Corporation of the United States, the feature of this paper is that after wrinkling, it undergoes calendering and has good mechanical porosity and appropriate elongation. It is an ideal material for the insulation of large transformer windings. Using it to wrap transpositive conductors can ensure tight wrapping without swelling.

04Nomex paper

It is a heat-resistant synthetic fiber paper produced by DuPont of the United States. Nomex is the trade name of this kind of fiber paper. The main component of Nomex is aromatic polyamide, which has excellent thermal aging properties. It can be used for a long time at 220℃ and belongs to Class C insulating materials.

05 Apply adhesive tape

It can be divided into three types: single-sided adhesive paper, double-sided adhesive paper and diamond-shaped adhesive paper. The adhesive paper type is made by coating 0.07mm wound paper with phenolic resin or epoxy resin and then baking and drying it.

06 Metallized paper

Used for floor screens and electrostatic screens. The base paper is 0.2mm thick insulating paper, and the aluminum foil thickness is 0.02mm. The insulating wrapping of the lead wire and the insulating screen.

07 Insulating cardboard

It is made by papermaking from sulfate wood pulp. It is used for oil-gap spacers, separators, cardboard cylinders, corrugated paper, yoke insulation, clamp insulation and end insulation winding pressure plates of disc windings.

08 Insulating Cylinder

The insulating tubes used in transformers include phenolic adhesive paper tubes, epoxy glass cloth tubes, fiberglass reinforced plastic tubes and cardboard tubes, etc.

09 Corrugated cardboard

In the oil plate gap structure composed of multiple paper tubes of high-voltage transformers, corrugated cardboard can be used to replace the support strips to form the oil gap. This insulating structure can save insulating materials on the basis of ensuring insulating performance.

10 Electrical laminated products

An insulating material with a layered structure, which is made by impregnating paper, cloth and wood veneer as the base material with different adhesives and then hot-pressing or rolling.

11Nomex cardboard

A cardboard made from a synthetic material based on aromatic amide fibers.

12 Pulling rod

The inter-stage rods, air gap struts, screws and bolts of the core columns of dry-type transformers often use glass fiber drawing rods.

13 Electrical thin molds and electrical composite materials

They all have excellent dielectric properties and belong to thin sheet insulating materials. Electrical films include polypropylene films, polyester films and polyimide films. Composite materials are composite products made by bonding fiber materials to one or both sides of a film.

14. Glass lacquer cloth

Glass varnish cloth is made by impregnating alkali-free glass cloth used by electricians with insulating varnish and then baking it. Used for dry-type transformers.

Insulating materials for transformer binding 15

The insulating materials used for transformer binding include cotton cloth tape, compression tape, semi-dry thin wire tape, mesh semi-dry non-weft tape, glass cloth tape and polyester rope, etc.