Short answer: DAR (dielectric absorption ratio) and PI (polarization index) are both ratios taken from a timed insulation resistance test with a megohmmeter. DAR is the resistance at 60 seconds divided by the resistance at 30 seconds — a one-minute check. PI is the resistance at 10 minutes divided by the resistance at 1 minute — a ten-minute… Read More: DAR vs PI: Reading Insulation Absorption Ratios »
If you’ve been doing motor insulation testing for any length of time, you’ve heard the standard cited a hundred times. “IEEE 43 says the PI minimum is 2.0.” “IEEE 43 requires correction to 40°C.” Most techs and engineers work from the rules without ever opening the document. That works fine until it doesn’t. Until an auditor asks where… Read More: IEEE 43-2013 Explained: A Clause-by-Clause Guide to Motor Insulation Testing… »
Most people who run a Polarization Index test can tell you the formula: 10-minute IR divided by 1-minute IR. Fewer can tell you why that ratio is meaningful, where it stops being meaningful, or what a result of 1.1 on a modern epoxy-mica winding actually implies — compared to the same reading on an asphaltic machine from 1965.… Read More: Polarization Index Testing of Motor Windings »
The polarization index test is the most reliable way to assess insulation condition on motors, generators, and other rotating machinery. It goes deeper than a standard 60-second megger reading and gives you a result that’s independent of temperature and equipment size. If you only have time for one insulation test on a critical motor, make it the PI… Read More: Polarization Index Test: What It Is, How to Do It,… »