Dielectric response of resin-rich insulation ageing characteristic for large generator

Abstract

This paper describes the research on the electrical ageing mechanism of the resin-rich molding (RRM) insulation by the dielectric response method for large generator. The dielectric properties of the RRM insulation materials with different ageing time were measured and analysed by dielectric temperature spectrum, frequency-domain spectrum (FDS) and thermally stimulated depolarization current (TSDC). The microscopic properties of the main insulation material were also analysed by scanning electron microscope and dynamic mechanical analysis. The results of the FDS measurements showed that the dielectric loss factor $$\tan \delta$$ and the real part e of the complex dielectric constant of the main insulation material increased significantly in the frequency range of 10−2–10 Hz as the ageing time increased; the fitting results of the double relaxation HN (Havriliak–Negami) model indicated that DC conductivity and interfacial polarization increased by the electric ageing effect in the main insulation. When the test temperature exceeded the glass transition temperature, the relaxation process of turning-direction polarization changed in the main insulation system; the TSDC tests indicated that the energy levels of the deep and shallow traps were slightly reduced during the main insulation's ageing, but the number of traps increased; therefore, the ability of capturing and releasing charges was enhanced in the main insulation.