Polarity Index Calculator for Insulation Resistance

This calculator helps determine the polarity index of insulation resistance measurements by comparing the resistance values measured with different polarities of test voltage. This is essential for assessing the quality of electrical insulation in equipment.

Input Parameters

Calculation Results

Calculation Formula

Polarity Index (PI) = Resistance (Positive Polarity) / Resistance (Negative Polarity)

Where:
PI = Polarity Index
Resistance (Positive Polarity) = Resistance measured with positive test polarity
Resistance (Negative Polarity) = Resistance measured with negative test polarity

Polarity Index Calculator for Insulation Resistance Calculator Usage Guide

Learn how to use the Polarity Index Calculator for Insulation Resistance calculator and its working principles

How to Use the Calculator

  1. Enter the resistance value measured with positive test polarity in megohms (MΩ)
  2. Enter the resistance value measured with negative test polarity in megohms (MΩ)
  3. Enter the test voltage used in volts (V)
  4. Enter the duration of the test in minutes
  5. Click the "Calculate" button to compute the Polarity Index and get recommendations

Understanding the Polarity Index

The Polarity Index (PI) is calculated as the ratio of insulation resistance measured with positive test polarity to the resistance measured with negative test polarity. A PI close to 1.0 indicates that the insulation is polarizing correctly, while a PI significantly different from 1.0 may indicate issues with the insulation.

Interpreting Results

  • PI between 0.95 and 1.05: Normal insulation condition
  • PI between 1.05 and 1.5: Slightly degraded insulation
  • PI between 1.5 and 2.0: Moderately degraded insulation
  • PI greater than 2.0: Severely degraded insulation

Principle of Operation

When a DC voltage is applied to insulation, charges within the material redistribute. The resistance measured with positive polarity will differ from that measured with negative polarity due to the time-dependent polarization processes. The Polarity Index helps assess the uniformity and quality of the insulation by comparing these measurements.

Applications

This calculator is useful for:

  • Electrical system maintenance and diagnostics
  • Condition assessment of transformers, motors, and other electrical equipment
  • Quality control during manufacturing and installation
  • Compliance with industry standards for insulation resistance testing