Abstract—The reliability of medium voltage (MV) motors used for driving pumps, fans, and other loads in the power generation in-dustry is critical for continued power production. Periodic testing of stator winding insulation, which is the most vulnerable compo-nent in MV motors, is an essential part of predictive maintenance for preventing unplanned reduction in the power generation capa-bility. Korea Electric Power Corporation (KEPCO) Research Insti-tute’s 17+ years of experience on predictive maintenance of stator insulation for MV motors is presented in this paper. KEPCO’s stator insulation test program and statistics of test records are summarized, and cases of recent turn and phase insulation failures that resulted in motor forced outages are investigated. Analysis of the turn or phase insulation failures and insulation test records performed on the failed motors show that it is difficult to predict turn or phase insulation failures with the insulation tests currently performed. Turn or phase insulation test methods are summarized and evaluated based on the findings of the investigation to help target future research efforts toward industrial needs.
Index Terms—AC machines, phase insulation, predictive maintenance, stator insulation testing, turn insulation.