Effect of field-induced dynamic parameters on the electric field distortion characteristic of high voltage oil-immersed bushing

Abstract

As an important component of oil-immersed transformers, the bushing's internal insulation ageing and dampness after the long-term operation can cause changes in the internal electric and temperature fields, seriously threatening its safe operation. This paper tested the power frequency permittivity and direct current conductivity of aged and damp oil-paper insulation samples at different testing temperatures, and constructed a dynamic dielectric parameter calculation model. Meanwhile, a simulation model was established based on the actual structure of the 252 kV/1250 A bushing which is mainly used for the oil-immersed high-voltage bushings of 110 kV and above. The electric-magnetic-thermal multi-physical fields were used for simulation analysis. The influence of ageing/moisture (different degrees of dampness in the upper and lower regions) on the electric field distribution in the bushing was obtained. During the initial to steady-state process, the electric field distribution at the zero and end shield shows a reversal phenomenon. When the capacitor core has different degrees of dampness in the upper and lower regions, the impedance distribution of the capacitor core is non-uniform. This phenomenon will lead to an increase in the radial electric field gradient at the end shield of the capacitor core, which is prone to the risk of slip-flashing discharge. In summary, this paper adopts the field-induced dynamic parameters method to analyse the changes of multi-physical fields in the bushing. This can provide theoretical guidance for optimising the bushing structure and on-site maintenance.