Study on Electrical Insulation Structure Optimization Design of Converter Transformer Bushing

Converter transformer bushing is main insulation structure connecting the inside and outside equipment of valve hall in HVDC transmission project. Its insulation structure can be divided into the oil-impregnated paper capacitance structure and the SF6 gas-epoxy impregnated capacitance core composite insulation structure. The latter has the outstanding advantages of low partial discharge level, good sealing performance and high safety. There are technical difficulties in converter transformer bushing, such as special operating conditions, complex physical and chemical properties of main insulation composite materials, and the various insulation coordination structures. Especially in (±800kV UHVDC) class, the power transmission is high, and the problems of the voltage equalization, field equalization and heat equalization of converter transformer bushing are prominent. The urgent research contents include: the physical and chemical properties test of epoxy impregnated paper composite insulating material under operating conditions, the optimum design of main insulation structure with large aspect ratio and multi-polar plate capacitor core, rule of eddy current heating and Joule heating of insulating medium for bushing metal current-carrying structure under high current, high voltage and multi-harmonic conditions.