Products such as insulation board and category 6 (mica board for electric heating equipment), category 2 (insulation paper), category 3 (insulation paperboard), category 8 and other products in category 7 are not allowed to follow the temperature index sort. The rest of the products should be classified according to the temperature index. The temperature index is not less than 105 code 1 and the temperature index is not less than 200 code 7. The main performance of insulating materials is 1.2. With the development of electrical technology, the capacity and voltage level of electrical equipment With continuous improvement, the working environmental conditions are increasingly expanding into multiple fields. Not only are insulating materials required to withstand the harsh tests of electricity, heat and various stresses, but also they must be able to withstand different external factors (such as high temperature, deep cold, space, ocean, high-energy radiation, etc.)
Therefore, the variety of insulating materials is required to continue to meet the needs of different conditions. Dielectrics are generally used in two different aspects: used as a support for electrical circuit components, and to insulate the components from each other and from each other; secondly, they are used as The dielectric properties of insulating materials usually referred to by capacitor dielectric mainly include dielectric constant, insulation resistance, capacitance, dielectric loss factor, electrical breakdown strength, etc. They are used to indicate the performance changes of the dielectric under applied voltage and the quality of the insulation. For example: when the dielectric constant is large, it indicates that the polarization of the dielectric is strong; when there is energy loss during polarization, the dielectric loss angle is too large; when there is a large leakage current, the volume resistance or surface resistance of the dielectric is not high Factors affecting dielectric performance include frequency, temperature, humidity, and electrical strength. There are only a few materials such as quartz material, polystyrene or polyethylene whose E and tan6 are almost constant in a wide frequency range. Insulation boards are used as engineering dielectric materials, while general dielectric materials must be used in The dielectric loss factor and dielectric constant are measured at frequency. The changes in dielectric constant and dielectric loss factor are caused by dielectric polarization and conductance. The most important changes are the dipole polarization caused by polar molecules and the interface polarization loss factor caused by the non-uniformity of the material. A maximum value can appear at the frequency.
This frequency value is related to the temperature of the dielectric material. The temperature coefficient of dielectric loss factor and permittivity can be positive or negative, depending on the location of the maximum value of dielectric loss factor at the measurement temperature; the degree of polarization increases with the amount of moisture absorbed or the formation of a water film on the surface of the dielectric material, As a result, the capacitance dielectric loss factor and DC conductivity increase. Therefore, it is essential to control the environmental humidity before and during the test. The significant effect of humidity often occurs below MHz and in the microwave frequency range; in the presence of interface polarization, the number of free ions increases with increasing electric field strength, and the size and location of the maximum loss factor also change accordingly. At higher frequencies, as long as there is no partial discharge in the dielectric, the permittivity and dielectric loss factor are independent of the electric field strength. In the following, some commonly used indexes indicating the dielectric properties and their meanings are classified.