Insulation materials are one of the most important materials in transformers, and their performance and quality directly affect the reliability of transformer operation and transformer service life.In recent years, new insulation materials used in transformer products have emerged in an endless stream.As an insulation group employee who deals with insulation parts every day, he should learn more and more comprehensive knowledge of insulation materials.In this training, the basic knowledge and latest developments of transformer insulation materials will be introduced.I hope that through training, we can enrich everyone's insulation knowledge and help in the production of insulation parts in the future.

1. Overview of transformer insulation materials.

With the rapid development of science and technology, electrical equipment such as motors and transformers are increasingly widely used.However, the reliability and service life of the transformer operation depend to a large extent on the insulation material used.Insulation materials are increasingly valued by those engaged in transformer design and manufacturing.

In the past two decades, new products, new technologies, and new theories in transformer insulation materials have continuously emerged and developed, so that transformer insulation materials and their applications have formed a very important discipline.

1.1 Introduction to insulating materials

Insulating materials, also known as dielectric, are materials with high resistivity and low conductivity.Insulating materials can be used to isolate conductors with charged or different potentials, so that current flows in a certain direction.In transformer products, insulating materials also play a role in heat dissipation, cooling, supporting, fixing, arc extinguishing, improving potential gradient, moisture-proof, mildew-proof, and protecting conductors.

Insulation materials are classified according to voltage level: generally divided into: Y (90°), A (105), E (120°C), B (130°C), F (155°C), H (180°C), C (greater than 180°C).

The heat resistance level of the transformer insulation material refers to the maximum temperature that the insulation material is allowed to withstand in the transformer.If the insulation material is used correctly, the service life of the material can be guaranteed for 20 years.Otherwise, it will be based on the 8C law (for every 8℃ increase in the insulation temperature of Class A, the service life will be reduced by half, the insulation of class B is 10℃, and the insulation of Class H is 12°℃.This law is called the 8°C law of thermal aging) reduces service life.The heat resistance of insulating materials composed of high-polymer materials is half lower than that of inorganic diemics.

The properties of insulating materials are closely related to their molecular composition and molecular structure.

There are many varieties of transformer insulation materials, which can be divided into gas insulation materials, liquid insulation materials and solid insulation materials according to their forms.

2. The four basic parameters of the electrical properties of transformer insulation materials.

The four basic parameters of the electrical properties of transformer insulation materials include insulation resistance, dielectric coefficient, dielectric loss factor and insulation strength.

2.1 Insulation resistance

2.1.1 The concept of insulation resistance

The resistance of an insulating material refers to the fact that the insulating material is pressurized for a long time under the action of a DC voltage, and the charging current and absorption current on the line disappear. Only the resistance value when the leakage current passes through/It is generally stipulated that after the voltage is added for one minute, the measured resistance value is the insulation resistance value.For high-voltage and large-capacity transformers, the insulation resistance is measured as pressurized for 10 minutes.

2.1.2 Factors affecting insulation resistance

2.1.2.1 The relationship between temperature and insulation resistance

As the temperature rises, the resistivity decreases exponentially. This is because when the temperature rises, the thermal movement of the molecules intensifies, and the average kinetic energy of the molecules increases, so that the probability of the molecular kinetic energy reaching the activation energy increases, and the ions are easy to transfer.

2.1.2.2 The relationship between humidity and insulation resistance

The water is immersed in the dielectric, which increases the conductive ions, and can promote the dissociation of impurities and polar molecules.Therefore, the insulating material decreases as the humidity increases, especially the insulating paper or insulating cardboard, the insulating resistance decreases even more.

The surface moisture of the dielectric has a very sensitive effect on its surface resistance. The attraction of hydrophilic materials such as ionic crystal polar materials to water is greater than the cohesion between water molecules, and the continuous water layer on the surface reduces the surface resistance.Therefore, the insulation resistance of electrical equipment is reduced due to moisture, resulting in excessive leakage current and damage to the equipment.

2.1.2.3 The relationship between impurities and insulation resistance

Impurities in the dielectric directly increase the conductive ions, causing the resistance to decrease, and the impurities are easily mixed into the polar material, promoting the dissociation of polar molecules and making more conductive ions.

The surface of the dielectric is contaminated by impurities, and the adsorption of moisture will cause the surface conductivity to decrease rapidly. The insulation resistance of the insulating material is one of the most sensitive parameters that reflect the amount of impurities in the material.In the standards of insulating materials, the method of measuring the volumetric resistivity is often used to measure the impurity content of insulating materials. In order to ensure the insulation level of insulating materials, insulating material factories must strictly control the cleanliness of the production environment.

2.1.2.4 The relationship between electric field strength and insulation resistance When the electric field strength is not too high, the electric field strength has little effect on the ion transfer capacity and the resistivity.When the electric field strength increases, the migration capacity of ions increases with the increase of the electric field strength, causing the resistivity to decrease. When the electric field strength increases to the point that the dielectric is close to breakdown, the resistivity decreases exponentially due to a large number of electron migrations.