| It is necessary to calculate surface electric field and parasitic capacitance parameters of converter valve shielding systems during the localization of High Voltage Direct Current (HVDC) technology. Supported by the Eleventh Five-Year Plan for National Science and Technology (Grant No.2006BAA02A27), the fast and accurate calculation of electric field based on Boundary Element Method (BEM) is studied. A new method called multi-coordinate and hybrid-weight-function BEM is proposed and proved to be efficient. It is used to analyze the electric field and capacitance of±800kV converter valves. The main innovative achievements are as follows:1. The study on Collocation and Galerkin approaches are carried out, which have their own advantages and disadvantages. The former is fast, while the latter is accurate. A new method, called multi-coordinate and hybrid-weight-function boundary element method (MCHWFBEM) is proposed. In this method, the Collocation and Galerkin procedures were synthetically employed to deal with the continuous integral equations. It makes full use of the advantages of the two procedures and provides a better trade-off between accuracy and efficiency. The availability of this method is demonstrated by comparing the calculated results obtained by MCHWFBEM with that obtained by finite element method (FEM) and Galerkin BEM.2. The calculation results of three-dimensional electric field of valve tower in DC converter station plays important directive role in the design of shielding covers for valve towers and the control of its surface field intensity. Based on BEM, much attention is paid to analyze the effect of chamfer on surface electric field of the shielding sheets by comparing computational field results of sheets with different chamfer situation. A simplified model for calculating surface electric field of valve tower is set up. By using MCHWFBEM and the model, the electric field in±800kV converter systems is obtained, which can be employed to guide insulation design of valve hall in HVDC converter stations in China.3. The parasitic capacitance parameters are most essential for modeling the equivalent wide-band circuit model of converter system, so a fast and accurate extraction of capacitance parameters plays an important role. According to HVDC converter substations, a simplified modeling method of capacitance extraction based on BEM is proposed. In the method presented, simulation model of the shielding sheets may not be chamfered. Consequently, the edge and corner of shield need not to be handled with sphere, cylinder and other curved surface. The availability of this modeling method is demonstrated by comparing the capacitance parameters of chamfered sheets with that of non-chamfered ones. It results in computation convenience and time savings and can be used in capacitance extraction of metal frameworks with large-size and complex structures. In addition, the effect of shielding covers in different layers on capacitance parameters is taken into account. Some regulations on simulation model are proposed to simplify the computation of parasitic capacitance.4. In order to improve the calculation efficiency, a new computational model called line-element which can apply to line structures such as Bus and Grading Ring is proposed. It is introduced into BEM to deal with complex electrical equipments. As a result, the computational accuracy and speed enhance dramatically. Analytical formulas for the maximum and minimum of 3-D sinusoidal steady-state field vector have been deduced based on phasor. It is demonstrated that the endpoint trajectory is an elliptical orbit in 3-D space by coordinate transformation. The formulas and conclution can be applied to analyze electric field near the complex equipments in AC substations.
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