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An accurate discrimination on moisture status of oil-impregnated paper (OIP) bushings is crucial for the maintenance and replacement schedule of bushings. Based on frequency-domain spectroscopy (FDS) measurement and Dissado–Hill (DH) relaxation model, this article proposes a hybrid approach of hidden Markov model and gray wolf optimization (GWO-HMM) for MS estimation of bushings subjected to the ununiform moisture distribution and dynamic time-series modeling. First, simulation models of moisture diffusion and FDS of the OIP bushing were constructed using finite element modeling approach. Then, the GWO algorithm was employed to explore dielectric parameters influenced by moisture in the DH model. Then, the GWO-HMMs was adopted as a classification tool to discriminate the MS of the simulation and experimental data of the bushings. Classification results confirm that the average identification accuracies of the proposed method are 97.17% and 96.81% over these two datasets, which demonstrates the effectiveness of the proposed moisture estimate method for OIP bushings. [ABSTRACT FROM AUTHOR]

When the inner insulation of oil-impregnated paper bushing breaks down in service, gases decomposed by oil and paper may cause an explosion. The explosion of bushing occurs from time to time because of the lack of an effective monitoring method. In order to provide an effective online monitoring method for the bushing to avoid explosion, this paper presents a method to monitor the PD defect in bushing by measuring the inner pressure of bushing. In this paper, the relationship of variation between characteristic gases content and inner pressure is studied, the effect of inner temperature on inner pressure is analyzed and the method for reducing this effect is also presented, and the monitoring method is proved to be useful by PD tests on a real bushing. The results show that the inner pressure increases obviously due to the generation of characteristic gases by internal discharge in oil-impregnated paper bushing, and the pressure increases with the deterioration of the discharge; although the inner pressure has a great influence on the inner pressure, the influence can be reduced or eliminated greatly by the method of common-mode rejection. According to the results, the internal discharge defect of the oil-impregnated paper bushing can be detected by monitoring the pressure, and the bushing explosion can be avoided.

Dielectric response techniques have been proven useful for evaluating the moisture content (Km.c) of oil‐paper insulation. However, an accurate model for oil‐paper condenser bushing has not been presented. This study designed a laboratory oil‐impregnated paper (OIP) bushing model to simulate moistened defects in oil‐paper bushings. Moreover, a 10 kV OIP bushing model was simulated using COMSOL multiphysics AC/DC to confirm that the distribution of potential meets the design requirements. Furthermore, this work investigates the effect of moisture content on the dielectric frequency response and polarisation and depolarisation current (PDC) of models of oil‐paper bushings. A group of characteristic parameters was extracted from the dielectric dissipation factor curves and the DC conductivities of different moisture contents were computed by charge difference method from PDC curves. The obtained results suggest that the dissipation factor and the capacitance increase with the increase of moisture content in the whole frequency range, and the quantitative relationships among the characteristic parameters, DC conductivities, and the moisture content were established and follow an exponential law. [ABSTRACT FROM AUTHOR]