A Brief Introduction of Insulating Material

Insulating materials are non-conductive materials under allowable voltage, but not absolutely non-conductive materials. Under the action of certain external electric field strength, conduction, polarization, loss, breakdown and other processes will occur, and aging will occur in long-term use. Its resistivity is very high, usually in the range of 1010-1022Ω·m. For example, in the motor, the insulation material around the conductor separates the turns from the grounded stator core to ensure the safe operation of the motor. Today, we will briefly introduce insulation materials.

Definition of Insulating Materials

Insulating materials, also known as dielectrics, refer to materials that are not conductive or have little conductive electrodes under DC voltage. Their resistivity is generally greater than 1010Ω·m. The main function of insulating material is to isolate charged conductors with different potentials in electrical equipment, so that current can flow along a certain path. It can also play the role of mechanical support and fixation, as well as arc extinguishing, heat dissipation, energy storage, moisture-proof, mildew-proof or improving the potential distribution of electric field and protecting conductors. Therefore, the insulation material is required to have as high as possible insulation resistance, heat resistance, moisture resistance, but also need a certain mechanical strength.

Basic Properties of Insulating Materials

(1) Breakdown strength

Under the action of electric field strength higher than a certain value, insulating materials will be damaged and lose their insulation performance. This phenomenon is called breakdown. The electric field strength of insulating material when it is broken down is called breakdown strength.

(2) Heat resistance

When the temperature rises, the resistance, breakdown strength and mechanical strength of insulating materials will decrease. Therefore, it is required that insulating materials can work for a long time at the specified temperature and the insulation performance can be guaranteed to be reliable. The heat resistance of insulation materials varies from different compositions. The heat resistance grade can be divided into seven grades: Y, A, E, B, F, H and C. The maximum working temperature of each grade of insulation material is stipulated.

(3) Insulation resistance

The resistance value of insulating material is insulating resistance. Under normal condition, the insulating resistance usually reaches more than tens of megaohms. The insulation resistance varies greatly with temperature, thickness and surface condition.

Although the resistivity of insulating material is very high, it is affected by certain voltage. There is always a small current passing through, which is called leakage current.

(4) Mechanical strength

According to the specific requirements of various insulating materials, the corresponding strength indexes, such as tension, compression, bending, shear, tear and impact, are collectively referred to as mechanical strength.

(5) Other characteristic indicators

Some insulating materials are presented in liquid form, such as various insulating paints, whose characteristics include viscosity, fixed content, acid value, drying time and gelling time. Some properties of insulating materials also involve permeability, oil resistance, elongation, shrinkage, solvent resistance, arc resistance and so on.

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