Research on insulation life evaluation and thermally induced pyrolysis mechanism of epoxy resin under high frequency electric stresses

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Abstract
The aging and functional failure of solid insulation materials are the key factors leading to irreversible failures of the gas-solid insulated DC power equipment, such as the voltage source converters. In order to accurately evaluate the insulation lifetime of the DC power equipment under special electric-thermal stresses, especially for the voltage waveform with high steepness, a temperature-controlled high frequency and high voltage test platform for insulation aging is designed, on which the life cycle of epoxy resin at different voltage frequencies (10-50 kHz) and temperatures (80-200 t) is studied. With the Weibull distribution function, the aging life data under various factors are analyzed, and a multi-factor insulation life evaluation formula under the laboratory conditions is proposed. To expound the microscopic mechanism of the frequency-dependent heating effect on the insulation lifetime, reactive molecular dynamic simulation is applied. The formation of the small molecules in the aging process is tracked to reveal the micro-pyrolysis mechanism of epoxy resin. The simulation results demonstrate that during the entire aging process, the gradual cleavage of the epoxy resin will release formaldehyde and acetylene gases, and formaldehyde variation can be utilized as a degradation index of epoxy pyrolysis. The full aging process of epoxy resin is studied from two aspects, namely experiments and microscopic simulation, from which the aging gas characterization parameters are obtained, and an aging life evaluation model is proposed, which presents useful reference for the insulation life study of the DC power equipment.

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