volume | PIER Journals

Abstract

Valve-side bushings in HVDC converter transformers operate under composite AC-DC electric stresses, where temperature-dependent conductivity induces significant redistribution of electric field. In this study, a unified electro-thermal coupled model is developed for a 226 kV capacitive grading structure. Two insulation margin indices corresponding to DC lifetime stress and AC partial discharge stress are defined, and a multi-objective optimization model is formulated to minimize the normalized variances of both margins. An improved multi-objective grey wolf optimizer with a nonlinear convergence factor and a crowding-solution screening mechanism is proposed to enhance convergence and Pareto-solution quality. Results show that the improved algorithm yields better Pareto-solution diversity and uniformity than the standard method, while the optimized structure reduces the maximum DC and AC electric fields by about 6.2% and 10.4%, respectively. The proposed method provides an effective design approach for improving insulation coordination and reliability of valve-side bushings under composite AC-DC stresses.

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Dr. Da Xie

Dr. Wei Wang

Mr. Yongchao Li

Dr. Siyi Wei

Dr. Gang Xu

Dr. Long Ma