What does a low polarization index indicate in an insulation test?

A low polarization index in an insulation test signifies that there is excessive moisture or contamination within the insulation material. The polarization index is a numerical ratio derived from measuring the insulation resistance at two different intervals, typically over a 10-minute period. A low index indicates that the insulation is not able to hold a stable resistive charge, which is a strong indication that moisture or contaminants are present, leading to a compromised insulation system. When moisture is absorbed by the insulation, it creates a path for electrical leakage, resulting in a lower measurement of insulation resistance. Thus, a low polarization index serves as an important diagnostic tool for identifying potential issues related to moisture ingress or contamination that could affect the integrity and functionality of electrical insulation.