The material which does not allow the electricity to pass through them is known as an electrical insulating material. The charge of the insulating material does not move freely, or in other words, it provides the high resistance path to the electric current through which it is nearly impossible for the electric current to conduct through it. Insulating material involves many industries such as electrical engineering, petrochemical, light industry, building materials, textile, etc.For instance,It is used in the overhead transmission line between the tower and conductor for preventing the flow of electric current from the conductor to earth. The electrical insulating material is also widely used in the electrical industries and it plays an important role in the development of electronic and electrical industries,etc.
Insulating materials are also called dielectrics. The main function of insulating materials is to isolate the live conductors with different potentials in the electrical equipment, so that the current can flow in a certain path, and also play an role in mechanical support and fixation, as well as arc extinguishing, heat dissipation, energy storage, moisture-proof, mildew proof or improving the potential distribution of the electric field and protecting the conductor.So the insulating material should have the following properties:
1.The material must have high mechanical strength so that it carries the tension and weight of the conductors.
2.They must have high dielectric strength.
3.The material is highly resistive for preventing the flow of leakage current from the conductor to earth.
4.The material is non-porous and free from impurities.
5.The electrical and chemical property of the material should not be affected by the temperature.
Insulating materials include gas insulating materials, liquid insulating materials and solid insulating materials.Except for insulating oil,the solid insulating material is commonly used in the electrical insulating material.
There are many kinds of solid insulation materials, which have excellent insulation performance and are widely used in power system. Commonly used solid insulating materials include: insulating paint, insulating rubber, fiber products, rubber, plastic and their products, glass and ceramic products, mica, asbestos and their products, etc.
Insulating paint and insulating adhesive are important insulating materials based on polymer, which can be solidified into hard insulating film or insulating material used in the whole insulating equipments under certain conditions.The polymer insulator material is used as an electrically insulating material. It is made up of a combination of fibreglass and an epoxy polymer instead of porcelain. The polymer material is puncture proof and has a high mechanical strength. It has high thermal resistance to reduce the damage of flash over, excellent radio interference voltage performance, lesser hardware corrosion, and better performance in polluted atmospheres.
The insulating paint is mainly composed of paint base, solvent, diluent, filler and other parts. After film-forming and curing, the insulating paint has high insulating strength, which can be used as immersion insulation or coating insulation for motor and electric coil. According to application, it can be divided into impregnating paint, enameled wire paint, covering paint, silicon steel sheet paint and anti corona paint.
The insulating glue is similar to the insulating paint, generally with filler, which is widely used for pouring cable joints, bushings, current transformers of 220kV and below, and voltage transformers of 10kV and below. The insulating adhesives used include yellow cable adhesive, black cable adhesive, epoxy cable adhesive, epoxy resin adhesive, epoxy polyester adhesive, etc.
Insulating fiber products refer to insulating materials made of insulating paper, cardboard, paper tube and various fiber fabrics. Impregnated fiber products are made of insulating fiber products as the base material, impregnated with insulating paint. It has certain mechanical strength, electrical strength, moisture resistance, and has some special functions such as mould proof, electricity proof and radiation proof. Insulating electrical laminated products are laminated structural insulating materials, which are made of fiber as the base material, dip coated with different adhesives, and hot pressed or rolled. Their performance depends on the base material, adhesive and their forming process. They can be made into products with excellent electrical performance, mechanical performance, heat resistance, mildew resistance, arc resistance, corona resistance and other characteristics.
Measures to prevent damage of electrical insulating materials
1. Do not use unqualified electrical products.
2.Select electrical equipment correctly according to working environment and use conditions.
3. Install electrical equipment or wiring correctly as specified.
4. Use electrical equipment according to technical parameters to avoid over voltage and overload operation.
5.Select insulating materials correctly.
6. Conduct insulation preventive test on electrical equipment according to specified cycle and project.
7. Improve the insulation structure properly.
8.During the transportation, installation, operation and maintenance, the insulation structure of electrical equipment shall be protected from mechanical damage, moisture and dirt.