Electrical Field Distribution in ±600 kV Converter Transformer Bushing Core with the Application of Epoxy Resin with Nonlinear Conductivity

The converter transformer as the conversion center for switching DC and AC is particularly crucial and is the key equipment of HVDC power system. As the weakness of the converter transformer, it is easy for the insulation failure to happen on the converter transformer bushing. Under load condition, the temperature rise on the conductor leads to an obvious temperature range and electrical field distortion along the radial direction of the bushing core. In this paper, the radial electrical field distribution of the ±600 kV converter transformer bushing was computed using the electric-thermal-fluid coupling model. Under full load condition, the radial temperature range in the bushing core causes the distorted electrical field strength to reach 12 kV/mm at the flange. Besides, the field strength in the SF
₆
is tripled at the top end of bushing. Normally micron-sized SiC/ZnO were added into the insulating polymers to obtain nonlinear-conductivity insulating composites, whose conductivities had very strong electrical field dependence when the field strength reached a certain value. When the bushing core is made of nonlinear conductivity epoxy resin, the field distortion at the flange is improved, which also decreases the field strength in the SF6 and oil. It is proved to be viable to suppress the electrical field distortion and decrease the insulation failures by the nonlinear conductivity epoxy resin.