Case studies of stator winding turn insulation failures in medium voltage motors

Breakdown of the stator winding turn insulation is a frequent cause of stator insulation failure leading to forced outage of medium voltage (MV) motors. Case studies of 15 turn insulation failures in mains-fed MV motors that occurred in Korea between 2011–2015 in the pulp and paper, power generation, and petrochemical industries are presented in this paper. The turn insulation failures are analyzed based on the insulation system design, motor operating conditions, fault location and pattern of the motor failures. Stator insulation inspection and test records including the insulation resistance (IR), polarization index (PI), leakage current, dissipation factor, and partial discharge (PD) tests for the failed motors are also shown. An insight into how stator winding turn insulation failures can be prevented is provided based on the investigation of the failures.