Theoretical calculation model of insulation medium and eddy current heating under complex waveform of ±800kV convertor transformer RIP bushing used in valve side

Abstract Electrical and thermal properties of the converter transformer valve side RIP DC bushing interact with each other, so electrical insulation failure in operation is directly related to the thermal properties. It is essential to conduct quantitative analysis on the power loss of UHV converter transformer dry-type bushing. The total power loss of bushing consists of two parts, eddy heat from current-carrying structures and joule heat from bushing core. The actual current and voltage waveform imposed on the bushing contain many high frequency components. In this paper, the theoretical calculation model of bushing core joule heat and eddy heat is obtained from structure of HV convertor transformer dry-type bushing. Then the temperature and frequency properties of epoxy impregnated paper used by dry-type bushing core are acquired by the experiments. Furthermore, based on the frequency domain FEM, the numerical calculation method for dry-type bushing power loss is proposed. In the end, the numerical results are used to analyze the factors that may lead to convertor transformer drytype bushing insulation failure in operation. The research result obtained in this paper is appropriate to compute thermal characteristic of bushing and is of directive significance to the operation, protection and accident analysis.