Development of insulation system to prevent local carbonization inside stator core of a product inverter-fed motor

A new phenomenon, called “local carbonization” inside a stator core was detected as a unique precursor to fragility of the insulation sheets of inverter-fed motors, and the conditions for generation of this carbonization were investigated. A separated stator of a product inverter-fed motor was manufactured, and an evaluation system for simulating a steep surge voltage was constructed. Electrically and mechanically, the results of a parameter survey of insulation system were used to compare the constructed separated stator and element model, and the comparison revealed a correlation between carbonization of the product separated stator and element model. From the consideration of carbonization mechanism, leakage current was revealed to be the dominant design factor. Through quantifying their threshold of carbonization occurrence, insulation system to prevent the carbonization in steeper inverter surge was developed by parameter survey using element model and validation test by separated stator. © 2021 Institute of Electrical Engineers of Japan. All rights reserved.