The insulating material is one of the most important materials in the transformer, its performance and quality directly affect the reliability of the transformer operation and the service life of the transformer. In recent years, new insulating materials used in transformer products have emerged in an endless stream. With the rapid development of science and technology, electrical equipment such as motors and transformers are widely used. However, the reliability and service life of transformer operation depend to a large extent on the insulating materials used. Insulation materials are more and more valued by those engaged in transformer design and manufacture. In the past two decades, new products, new technologies, and new theories of transformer insulation materials have emerged and developed continuously, so that transformer insulation materials and their applications have formed a very important discipline.
Insulating materials, also known as dielectrics, are materials with high resistivity and low conductivity. Insulating materials can be used to isolate conductors that are charged or at different potentials, allowing current to flow in a certain direction. In transformer products, insulating materials also play a role in heat dissipation, cooling, support, fixing, arc extinguishing, improving potential gradient, moisture-proof, mildew-proof, and conductor protection. Insulation materials are classified according to the voltage level: generally divided into: Y (90°C), A (105), E (120°C), B (130°C), F (155°C), H (180°C), C (greater than 180°C ℃). The heat resistance grade of the transformer insulation material refers to the maximum temperature that the insulation material is allowed to withstand in the transformer. If the insulation is used correctly, it can guarantee a 20-year lifespan of the material. Otherwise, it will be based on the 8°C law (for every 8°C increase in the temperature of Class A insulation, the service life will be reduced by half, Class B insulation is 10°C, and Class H is 12°C. This law is called the 8°C law of thermal aging). service life. The heat resistance of insulating materials composed of high 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 kinds of transformer insulating materials, which can be generally divided into gas insulating materials, liquid insulating materials and solid insulating materials according to their forms.
Solid insulating material: The solid insulating material used in the transformer refers to the insulating material which is solid in the form of the material itself or becomes solid after chemical reaction and physical change. There are many kinds 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 tape, shrink tape, Mesh latitude polyester belt, etc.
1. Insulation paper
The insulating paper mentioned here refers to pure sulfate wood pulp paper, and other insulating papers include synthetic fiber paper (such as NOMEX paper), nitrile-added insulating paper (such as Denison paper) and so on.
2. Insulating crepe paper
It is made of insulating paper for electricians through crumpling. There are wrinkles along its transverse direction, and the wrinkles are pulled apart when stretched. Due to different creping procedures, crepe paper with different elongation can be made. The thickness of insulating paper is generally 0.05mm~0.12mm, and the elongation range is 5%~200%. Insulating crepe paper is often used for winding insulation of oil-immersed transformers, such as the winding head,
3. Denison paper
The modified insulating paper is called nitrilized paper. During the manufacturing process, bis-nitrile amine, vinyl cyanide, etc. are added to the pulp. Produced by Denison Corporation of the United States, it is characterized in that the paper has good mechanical cyan degree and appropriate elongation after being crumpled and calendered. It is an ideal material for large-scale transformer winding turn insulation. Using it to wrap transposed wires can ensure Pack tightly without swelling.
04. Nomex paper
It is a heat-resistant synthetic fiber paper produced by DuPont Company of the United States. Nomex is the trade name for this fiber paper. The main component of Nomex is aromatic polyamide, which has good heat aging properties. It can be used for a long time at 220°C and belongs to Class C insulating material.
05. Adhesive paper
It can be divided into three types: single-sided adhesive paper, double-sided adhesive paper and rhombus adhesive paper. The gummed paper type is made by coating phenolic resin or epoxy resin on 0.07mm winding paper and then baking and drying.
06. Metallized paper
For ground screen and electrostatic screen. The bottom paper is 0.2mm thick insulating paper, and the aluminum foil thickness is 0.02mm for the insulation wrapping of leads and insulating screens.
07. Insulated cardboard
Made from kraft wood pulp paper. It is used for oil gap pads, separators, cardboard tubes, corrugated paper, iron yoke insulation, clip insulation and end insulation winding pressure plates for cake windings.
08. Insulation barrel
The insulating tubes used in transformers include phenolic adhesive paper tubes, epoxy glass cloth tubes, glass fiber reinforced plastic tubes and cardboard tubes.
09. Corrugated cardboard
In the oil plate gap structure composed of multi-layer paper tubes for high-voltage transformers, corrugated cardboard can be used instead of stays to form oil gaps. This insulating structure can save insulating materials on the basis of ensuring the insulating performance.
10. Electrical laminated products
It is a layered insulating material made of paper, cloth and wood veneer as the substrate, dip-coated with different adhesives, and hot-pressed or rolled.
11. Nomex cardboard
A cardboard made from a synthetic material based on aramid fibers.
12. Drawing rod
The interstage rods, air gap stays, screw rods and screws of the dry-type transformer core columns often use glass fiber rods.
13. Electrical thin mold and electrical composite materials
With excellent dielectric properties, they all belong to thin sheet insulating materials. Electrical films include polypropylene film, polyester film and polyimide film. Composite materials are composite products made by bonding fiber materials to one or both sides of a film.
14. Glass varnished cloth
Glass varnish is made of alkali-free glass cloth for electricians soaked with insulating varnish and baked. For dry-type transformers.
15. Insulating materials for transformer binding
The insulation materials used for transformer binding include cotton cloth tape, shrinkage tape, semi-dry thin wire tape, mesh semi-dry latitude-free tape, glass cloth tape and polyester rope.