When measuring with an insulation resistance tester, the insulation resistance value does not immediately stabilize at a certain number, but gradually increases from small to large over time - this process is called the "absorption process", which leads to an important parameter for measuring insulation state: absorption ratio DAR.

The absorption process of insulation

When a high voltage direct current is applied to the insulation material, the total current flowing through the insulation is composed of three parts: capacitor charging current (rapidly decaying, lasting for about a few seconds), absorption current (slowly decaying, lasting for several minutes), and stable leakage current (constant value).

Therefore, the insulation resistance has the lowest measured value in the first few seconds of the test (due to the high charging current of the capacitor), and then continues to rise over time until the absorbed current decays and stabilizes. That's why the standard specifies that the insulation resistance is usually read (R60) 60 seconds after applying voltage, rather than immediately.

Definition of Absorption Ratio DAR

DAR (Dielectric Absorption Ratio)=R60/R15

The ratio of insulation resistance at 60 seconds to insulation resistance at 15 seconds.

HZJY-30KV automatically records the resistance values of R15 and R60 at the beginning of the test, and calculates and displays DAR after 60 seconds without the need for manual timing or calculation.

Judgment criteria for DAR

When the insulation is damp, the leakage current is large and the absorption process is not obvious. The difference between R15 and R60 is very small, and the DAR is close to 1; Dry and well insulated, with obvious absorption process, R60 significantly higher than R15, and higher DAR value.

Industry standard judgment reference:

DAR ≥ 1.6: Good insulation, dry

1.4 ≤ DAR<1.6: Insulation is basically normal, closely tracked

DAR<1.4: Suspected insulation, further check for moisture or aging

There are slight differences in the threshold requirements for DAR among different devices and regulations, and the regulations applicable to specific devices should prevail. The overall logic is: the higher the DAR, the better the insulation; The closer the DAR is to 1.0, the more likely the insulation has become damp.