Anisotropy in Dry-Type Valve-Side Bushings of Converter Transformer: Phenomena and Effects

Abstract

The safe and stable working of dry-type valve-side bushings, important components of converter transformers, is essential. In recent years, poor design has led to several core breakdown, flashover and cracking failures. The bushing cores, composed of crepe paper and aluminium foil, exhibit significant anisotropic physical properties due to its arrangement. However, in previous designs and simulations, the epoxy resin impregnated paper (ERIP) material of the core is often treated as isotropic, and even combined with aluminium foil for the thermal and mechanical calculations. This simplification results in considerable deviations between simulated and actual performance. In this paper, radial and axial ERIP slices are prepared and their electrical, thermal and mechanical anisotropy parameters are measured. A new modelling method of bushing anisotropy is proposed. Based on COMSOL Multiphysics 6.2, the electrical–thermal–mechanical–fluid simulation model of ± 800 kV dry-type valve-side bushing is established. The results indicate that the anisotropic model exhibits a 19.1% higher temperature rise, a 15.2% higher maximum radial field strength, and an 85.7% lower damage stress margin than those of the isotropic model. These results show that bushing anisotropy cannot be ignored in modelling and design.