Since 1997, Iris Power has been collecting PD test results and statistically analyzing them every two years. With now over 1 million test results in the database, it has become clear that the statistical distribution of peak PD magnitudes (Qm), and especially the “Alert” levels (the level where the Qm is higher than 90% of readings from similar machines), has become stabile for most types of machine ratings. That is, even though we were essentially analyzing completely new data every two years (since we only use the most recent test for each biennial analysis), the Alert level for significant stator winding PD remained essentially the same. Please note that the statistical distributions of Qm, and thus the Alert levels, depend on the operating voltage and pressure of the machine as indicated in Severity Tables (PDF).
Since the biennial analysis is not changing the Alert levels, Iris Power will discontinue regular biannual analysis, and use the results presented at Iris Conference in 2023 for the interpretation of PD test results. We will continue to verify statistical distribution of peak PD magnitudes and issue new Severity Tables if required.