Polarisation Index = R₁₀min / R₁min from a megger test. IEEE 43 minimum acceptable PI ≥ 2.0 for most machines.
Formula
$$ PI = \frac{R_{10 \text{ min}}}{R_{1 \text{ min}}}, \quad DAR = \frac{R_{60 \text{ s}}}{R_{30 \text{ s}}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $R_{t}$ | Insulation resistance at time t | MΩ | megger test |
| $PI$ | Polarisation index | - | IEEE 43 |
| $DAR$ | Dielectric absorption ratio | - | IEEE 43 |
Sources
- IEEE 43 - Recommended Practice for Testing Insulation Resistance.