Publication

Abstract : This paper proposes a novel method to analyze the relaxation behavior of epoxy mica insulation under accelerated thermal ageing conditions using Havriliak-Negami (H-N) relaxation model. The epoxy mica composite insulation was subjected to thermal ageing for 200 hours, 400 hours and 600 hours, respectively, at 150°C. Then, frequency domain spectroscopy (FDS) measurement was performed on the insulation samples from 0.1 mHz to 1 kHz to record the real part ε′(ω) and imaginary part ε″(ω) of complex permittivity ε*(ω), respectively. From the recorded FDS data, real part M′(ω) and imaginary part M″(ω) of complex dielectric modulus spectrum M*(ω) was computed to unmask the dielectric relaxation, which is suppressed due to conductivity effect at very low frequencies. Then M′(ω) and M″(ω) computed at each measurement frequency were plotted and their variation was modelled using H-N relaxation model. Investigations revealed that parameters of H-N model are sensitive to thermal ageing. Finally, two empirical relationships have been developed between the H-N model parameters with ageing duration to estimate the ageing state of the epoxy-mica insulation quantitatively.