Accelerated Aging Procedure and Online Method for Stator Insulation Monitoring of Induction Motors

Online methods for stator insulation monitoring have been investigated with increasing interest in the last 15 years. These methods rely on the high-frequency behavior of the electric machine. In converter-fed machines, the high-frequency behavior is visible through the current ringings occurring during the switching commutations of the power electronics. As the lifetime of electric machines can last several decades, a faster way to evaluate insulation monitoring methods is through accelerated aging tests. This work aims to perform an accelerated aging procedure on an induction motor to test an online insulation monitoring method. The motor has a randomly-wound stator winding and it is aged by means of thermal cycles without the need for an oven. A custom converter is employed during the accelerated aging procedure to apply the thermal cycles and to record the current ringings. The proposed insulation monitoring method is based on a metric that quantifies the current ringing variations in a simple manner, following the quasi-linear variation of the parasitic capacitances during the motor aging.