Polarization index PI = R(10 min) / R(1 min), the dielectric absorption rate DAR = R(1 min) / R(30 sec) It is found using the following: According to IEEE 43, PI <1 is risky, 1–2 is suspicious, 2–4 is good, >4 is excellent. For example, for R₁=500 MΩ and R₁₀=2000 MΩ, PI = 4.

PI = R(10 min) / R(1 min) DAR = R(1 min) / R(30 sec)
Example calculation: R(1 min)=500 MΩ, R(10 min)=2000 MΩ → PI = 2000/500 = 4 → insulation condition is excellent (IEEE 43).

Insulation Polarization Index (PI/DAR)

Calculate the polarization index (PI) and dielectric absorption ratio (DAR) from time-lapse insulation resistance measurements; evaluate the insulation condition.

Polarization Index (PI)
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NARROW
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Notes: PI = R(10 min) / R(1 min) · DAR = R(1 min) / R(30 sec). Overall assessment (IEEE 43): PI <1 risky, 1–2 questionable, 2–4 good, >4 excellent. In modern low-absorption insulation, low PI is also acceptable due to high initial resistance; the result is evaluated in conjunction with temperature and humidity.
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How is it calculated?

  1. Enter the insulation resistance at 1 minute (R₁) and 10 minutes (R₁₀).
  2. (Optional) Enter the 30-second resistance (for DAR).
  3. Press Calculate; PI, DAR, and insulation status will be displayed.

Frequently Asked Questions

What should the polarization index be?
According to the IEEE 43 general evaluation, a PI of 2–4 is good, above 4 is excellent; a PI below 1 may indicate insulation problems.
What is the difference between PI and DAR?
PI stands for 10 minutes/1 minute, while DAR stands for 1 minute/30 seconds, providing a quicker overview in a shorter time.
Is a low PI always bad?
No. In modern low-absorption insulation, a low PI is acceptable if the initial resistance is already very high; the result is interpreted in conjunction with temperature and humidity.

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