Polarization index is a ratio of the measured insulation resistance at what two specific intervals?

The Polarization Index (PI) is an important measure used in the evaluation of insulation health and integrity, particularly for electrical equipment. It specifically assesses the insulation resistance of a system over a specified period to give insights into its condition. The PI is calculated by taking the insulation resistance measured at a longer duration, typically 10 minutes, and dividing it by the measurement taken at 1 minute.

This ratio is significant because it reflects how well the insulation is able to withstand voltage over time. A higher PI value usually indicates better insulation quality, while a low value could suggest potential insulation issues, such as moisture or deterioration.

The other intervals provided in the options do not align with the standard practice for calculating the Polarization Index. The use of 10 minutes compared to 1 minute is well established in industry guidelines, making this pairing the correct context for assessing insulation resistance with respect to time.