Insulating materials are non-conductive materials under allowable voltage, but not absolutely non-conductive materials. Under the action of a certain electric field intensity, conduction, polarization, loss, breakdown and other processes will occur, and long-term use will also occur aging.
The resistivity is very high, usually in the range of 1010 ~ 1022 Ω m.. For example, in a motor, the insulation material around the conductor isolates the turns and the grounded stator core to ensure the safe operation of the motor.
Insulation material is also called the dielectric, the resistivity generally greater than 1010 Ω m.. The main function of insulating materials is to isolate the live conductor with different potential in the electrical equipment, so that the current can flow according to a certain path, but also can play a role in mechanical support and fixation, as well as arc quenching, heat dissipation, energy storage, moisture-proof, mildew or improve the electric field potential distribution and protect the conductor. Therefore, insulation materials are required to have as high as possible insulation resistance, heat resistance, moisture resistance, also need a certain degree of mechanical strength.