What are the factors that affect resistance measurement? Why test the electrical properties when the sample is to be treated?
At the beginning of the polarization current is very strong, with the increase of pressure time, the value of the current decreases, the insulation resistance increases, this phenomenon is called absorption phenomenon. In the absorption phenomenon, the fastest decay current is called capacitance current, current varies slowly with time is called the absorption current, the stable current with time change is decided by the media called the conductance of the conduction current. General equipment capacity is bigger, this phenomenon is more obvious. Due to time varying current absorption, so in a specified time to test the insulation resistance and leakage current.
When the insulation damp or dirty, leakage current increases, the absorption phenomenon is not obvious. Factors affecting the insulation resistance measurements include temperature, humidity and discharge time. Because of the high temperature makes the dielectric polarization intensified, resulting in the increase of conductivity, resistance is reduced, thus the insulation resistance decreases with the temperature increasing. The insulation surface due to moisture absorption or porcelain water film formed on the surface of the insulation insulation resistance decreased significantly. In addition, when the insulation in high relative humidity will absorb more moisture, so that the increase in conductance, reduce insulation resistance test. The insulation resistance equivalent insulation applied DC high voltage charge, so the sample is charged, after the test sample should be fully discharge, and the discharge time should be greater than the charging time, and not due to residual charge could not be exhausted, and the charging current obtained in repeated measurements and the absorption current than the first measurement value is small, so The decrease of absorption ratio and the increase of insulation resistance
Some insulation objects (such as: plastic, porcelain etc.) under DC voltage, the conduction current instant can reach a stable value, but for generators, transformers, motors, cables and other electrical equipment, which is composed of composite insulation medium in DC voltage, will produce a variety of polarization phenomena.
