Evaluation and Improvement of Insulation Resistance in Induction Motor Stators Using Corrective Maintenance Methods

The reliability of induction motors is strongly influenced by the condition of stator insulation, which commonly deteriorates due to thermal stress, humidity, contamination, and aging. Severe degradation of insulation can cause unexpected breakdowns, power losses, and reduced equipment lifetime. This study aims to evaluate and restore the insulation resistance of a three-phase induction motor through systematic measurement and corrective maintenance.The research was conducted in several stages, beginning with the measurement of insulation resistance using a megohmmeter. The initial results showed values of 0 MΩ for both phase-to-phase and phase-to-ground across all sessions, indicating that the insulation system had completely failed. These values were then corrected to a reference temperature of 40 °C in accordance with IEEE Std 43-2013 to allow accurate comparison. The causes of degradation were identified as contamination, moisture ingress, high operating temperature, vibration, and natural aging of insulation materials. Corrective maintenance actions were applied, including cleaning, drying, varnish impregnation, reinforcement, and complete rewinding. After maintenance, the corrected insulation resistance values improved significantly, reaching up to 2000 MΩ in all sessions, far exceeding the IEEE threshold of 100 MΩ. This improvement demonstrates that the applied methods successfully restored the dielectric integrity of the stator insulation. In conclusion, systematic testing combined with corrective maintenance ensures the recovery of insulation performance, supports reliable motor operation, and extends service life.