What is polarization index and absorption ratio

Polarization index (PI) and absorption ratio (DAR) are tests to check whether the leakage current of the insulator increases in time. It is confirmed that the leakage current does not increase while the application time is applied. The meter automatically calculates the polarization index PI and absorption ratio DAR value as a judgment Judgment of insulation performance, polarization index PI and absorption ratio DAR all indicate the change of insulation resistance within a period of time after the measured object is subjected to the measurement voltage.

Absorption ratio

Absorption ratio: In the same insulation resistance test, the ratio of the insulation resistance value at 1 minute to the insulation resistance value at 15 seconds.

Polarization index

Polarization index: In the same insulation resistance test, the ratio of the insulation resistance at 10 minutes to the insulation resistance at 1 minute.

Why measure insulation resistance absorption ratio and polarization index

In the insulation resistance test, the insulation resistance value at a certain moment cannot fully reflect the insulation performance of the tested product. After the insulation material is applied with high voltage, there is a process of absorption ratio and polarization process of the charge. Therefore, the power system It is required that the absorption ratio and polarization ratio should be measured in the insulation test of main transformers, cables, motors, etc. to determine the quality of the insulation condition. The absorption ratio or polarization index in the insulation resistance measurement can reflect the moisture content of the generator or main transformer insulation. After the insulation is damp, the absorption ratio or polarization index decreases, so it is an important indicator to judge whether the insulation is damp.

Measurement of insulation resistance absorption ratio and polarization index

In engineering, insulation resistance and absorption ratio (or polarization index) can reflect the degree of dampness of the insulation of generators, oil-immersed power transformers and other equipment. After the insulation is damp, the absorption ratio (or polarization index) value decreases, so it is a judgment An important indicator of whether the insulation is damp, it should be pointed out that sometimes the insulation has obvious defects (for example, insulation breakdown under high voltage), the absorption ratio or polarization index value is still very good, the absorption ratio or polarization index cannot be used to detect moisture , For other local insulation defects other than dirt, the digital insulation resistance meter can accurately measure the change of insulation resistance within a period of time after the measured object is subjected to the measured voltage.