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The high-voltage isolated energy supply transformer (HIET) is the key component of the HVDC breaker, which is used for energy transmission and the potential isolation. There is a lack of research results that can meet engineering applications at home and abroad. The design of a 500 kV HIET with dry-type insulation is proposed, using 10 cascade connected 50 kV sub-transformers (STs), which uses silicon rubber suitable for DC voltage as the main insulation material. High-voltage (HV) winding of ST adopts double-shielding structure of coil semi-conductive shielding and inner semi-conductive shielding to improve electric field distribution. The simulation analysis of an electric field at different insulation thicknesses and temperatures shows that the electric field decreases with an increase in thickness of insulation. When the thickness is greater than 25 mm, the electric field reduction effect is significantly weakened. The electric field is closely related to temperature, when at 20°C, the electric field between double-shielding is relatively uniform. When at 70°C, the inner shielding electric field is much higher than coil shielding, and undergoes obvious reversal. In addition, the 500 kV HIET's electric field has been analysed. The 50 0kV HIET prototype has been manufactured and passed the type test, and successfully applied to the 500 kV Zhangbei DC grid project.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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