What are the factors that affect the insulation resistance?

 

       Second, the factors affecting the insulation resistance are mainly as follows:

       1. The effect of temperature
       The operating temperature of a power device varies with the surrounding environment, and its insulation resistance also varies with temperature. In general, the insulation resistance decreases as the temperature increases. The reason is that when the temperature rises, the ions and molecular motion inside the insulating medium are intensified, and the moisture in the insulator and the impurities and salts contained therein also diffuse, which leads to an increase in conductance and a decrease in insulation resistance. This is not the same as the resistance of the conductor as a function of temperature. Different electrical equipment and electrical equipment made of different materials have different insulation resistances with temperature, and it is difficult for on-site children to ensure that they are carried out at a completely similar temperature. In order to compare the test results, the relevant units have given some temperature conversion factors for the equipment. However, due to the obsolescence of the equipment, the degree of drying, and the temperature measurement methods used, there are many influencing factors, and it is difficult to obtain an accurate conversion factor. Therefore, when actually measuring the insulation resistance, the test temperature (ambient temperature and equipment body temperature) must be recorded, and measurements should be made at similar temperatures as much as possible to avoid errors caused by temperature conversion.

       2. Humidity and effects of surface contamination of electrical equipment
       The change of the ambient humidity around the power equipment and the surface contamination caused by the air pollution have a great influence on the insulation resistance. When the relative humidity of the air increases, a large amount of moisture is adsorbed on the surface of the insulator, so that the surface conductivity increases and the insulation resistance decreases. When the surface of the insulator forms a continuous water film, the insulation resistance is lower. According to the above two conditions, when measuring the insulation resistance on site, the shielding ring must be used to eliminate the influence of surface leakage current or to dry and clean the surface of the equipment to obtain the true measured value.