The impact of high potential (Hipot) testing on globally VPI´ed stator winding

High potential (Hipot) tests have long been used by many on machine stator windings to assess the integrity of electrical insulation system in question. Most industrial standards limit those recommended test values on completed new machines ready for service or existing machines under service/maintenance conditions. There is only limited information available in the literature regarding tests done on globally VPI´ed windings at pre-VPI green coil and/or green winding stages, and its impact on insulation life. We are aware that a limited few users do specify green coil test requirements, with some of those criteria significantly different than our in-house test standard that has been used for many years with proven effectiveness. This study is to compare these two different test philosophies, to see the advantages and disadvantages between them, and to check whether those different test approaches would affect the ultimate goal: the long term insulation reliability of machines in service.