Affiliations: [a] Hebei Provincial Key Laboratory of Power Transmission Equipment Security Defense, North China Electric Power University, Baoding, China | [b] North China Electric Power University, State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, Beijing, China
Correspondence:
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Corresponding author: Gang Liu. Department of Electrical Engineering, North China Electric Power University, Baoding 071003, China. Tel.: +86 3127522854; E-mail: liugang@ncepu.edu.cn
Abstract: The voltage on the valve side windings of the converter transformer is non-sinusoidal, which contains many high-order harmonic components. To calculate the nonlinear electric field distribution under the non-sinusoidal voltage, the harmonic-balanced decomposition finite element method (HBDFEM) is proposed in this paper. By using the fixed-point method, the finite element stiffness matrix of each iteration is decomposed according to the harmonic order, by which the memory consumption can be remarkably reduced. To verify the effectiveness of the proposed algorithm, a typical model of the oil-paper insulation structure is taken for instance, and the results obtained by the HBDFEM is compared with two algorithms, the traditional HBFEM and the time step method. The calculation results show that the HBDFEM can effectively reduce the computation cost for the nonlinear electric field problems with the non-sinusoidal periodic voltage. And it can be applied to analyze the compound electric field problems of the actual converter transformer. The electric field distribution of a ±500 kV converter transformer is calculated and analyzed considering the nonlinear relationship between the electric field and the medium conductivity.
Keywords: Converter transformer, fixed-point, finite element method, electric field, harmonic-balanced method
