Comparison of impedance spectroscopy and partial discharge analysis as insulation health diagnosis techniques

Abstract

The ageing of insulation systems in electric machines can compromise partial discharge-free designs. Regularly monitoring insulation health is crucial to prevent unexpected failures. Several authors have proposed health markers from impedance spectroscopy and partial discharge analysis. Nevertheless, no comparative study has evaluated their sensitivity as health monitoring techniques for complete windings tested until failure. This paper compares both techniques for a thermally aged electric machine winding until failure, with impedance spectrum and partial discharge measurements taken every 24 hours. Markers from impedance spectroscopy (resonance frequency, impedance above/below resonance frequency, and capacitance) and partial discharge measurements (partial discharge inception voltage and charge) were compared considering: (1) deteriorated insulation identification, (2) sensitivity to changes in the insulation, and (3) near breakdown indication ability. While impedance spectroscopy markers varied with ageing, partial discharge analysis proved more meaningful. Regular monitoring of partial discharge inception voltage and charge can identify deteriorated insulation and prompt necessary maintenance.