An approach for computer modelling of dielectric relaxation, effective dielectric properties and local characteristics (electric fields and power losses) of the composites is presented. Simulations are performed for binary mixtures with regular and stochastic structures using experimentally obtained frequency dependent properties of the constituent phases as input parameters. The model is verified by comparing the computed results with the experimental data. The developed procedure is then applied to analyze interfacial charges, fields and losses in a water-treed polymeric insulation of a high voltage cable.
Frequency response analysis (FRA) is usually used for diagnostics of mechanical deformations and displacements of transformer windings caused by electromagnetic forces during short circuits. In general, a high frequency response of a transformer is affected by the properties of all transformer components, and, thus, the FRA carries information about the state of the whole transformer including its main electrical insulation. From this point of view, the FRA might be considered as an alternative to the existing methods for assessment of the insulation. In the present paper, the applicability of the FRA is analysed using a high frequency model of a transformer, which takes into account the complex structure of the oil-paper insulation and frequency dependencies of the dielectric permittivities of the insulation components as well as winding resistances. A sensitivity analysis of the computed frequency responses to the variations in geometrical structure and complex permittivities of the components is presented.
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