Jiansheng Yuan

Calculation of the potential distribution of high voltage metal oxide arrester by using an improved semi-analytic finite element method

This paper proposes a semi-analytic finite element method to treat the open boundary axisymmetric electrostatic field problems. The method is applied to computing the potential distribution of the high voltage porcelain metal oxide arrester (MOA). The numerical example shows a good agreement between the calculated and measured results.

Simulation of substation grounding grids with unequal-potential

A method of forming the equation system for simulating substation grounding grids with unequal-potential, i.e., the potential drop caused by the interior resistance of conductors is taken into account, is presented, based on a theory of combination of field and circuit. The equation system with the potential at discretization points of the grid as unknowns is formed by the method of node analysis in the circuit theory, and the definition of the mutual-resistance between conductors located in conducting media concerns with the electric current field theory. The method presented is capable of calculating the grids with arbitrary structure and floating electrodes in multiple-layer earth models. Comparison of calculation results of grids by equal and unequal potential models is given.

A three-component boundary element algorithm for three-dimensional eddy current calculation

A three-component boundary element algorithm for the calculation of 3-d linear eddy currents is presented in this paper, which employs an imaginary magnetic charge scalar and an imaginary current density vector with two components, distributed over the interfaces of different regions, as unknowns. The simplified expression of the current density vector by two components instead of three ones is based on that the current density has no perpendicular component relative to the interface. This reduction of one component can save about 40% computer memory and 50% computer time in the solution of the boundary element equation. Some eddy current problems have been calculated successfully by this algorithm. >

Determination of three-layer earth model from Wenner four-probe test data

Based on the solution of the electric field inverse problem, an efficient method for determining three-layer earth models and parameters from Wenners four-probe test data is presented, i.e., from a set of voltage values measured on the earth surface due to the current injected into the earth. The speed of the iterative convergence is increased by employing the generalized inverse algorithm for solving the relevant nonlinear system of equations, and using a suitable method for determining initial values for the iterative process. The earth structure is the field model for simulating grounding electrodes or grounding grids of substations. The determination of the structure is essential in the simulation and the design of grounding grids.

Design of novel structure current transformer with shielding coils for overcoming the saturation of core

The core saturation of current transformers is one of the key obstructions in the development of highly reliable protective approaches and devices of power systems. A novel structure current transformer with shielding coils is introduced and analyzed in this paper. The coils are enwound outside the measurement winding of the current transformer, and each couple of coils are located at the opposite position relative to the diameter of the core, and connected in opposed-polarity. With the opposed-polarity connecting coils the magnetic field in the core produced by its adjacent phase current in a three-phase system can be shielded, so that the core saturation can be avoided. However, the coils do not influence the main magnetic flux that is caused only by the same phase current

The complex image method and its application in numerical simulation of substation grounding grids

In the simulation of electromagnetic fields produced by a point source located in multilayer media, the conventional image method requires an infinite number of images, while the method of complex images only needs a few ones to get an accurate solution. Based on the method of complex images, an approach for simulating grounding systems in multilayer soils is introduced in this paper, and the corresponding Green functions are derived. Software for simulating grounding systems in up to six-layer soils has been developed, and the grounding systems with any complicated structure can be located anywhere in multilayer earth models. Copyright

Simulation of bipolar charge transport with trapping and recombination in polymeric insulators using Runge–Kutta discontinuous Galerkin method

The widely used QUICKEST method with ULTIMATE flux limiter is not capable of solving the charge transport problems with a very steep wavefront accurately, due to the wide stencil adopted. Furthermore, the splitting process of separating the convection and the reaction terms in the method introduces additional errors. To solve such problems accurately, a novel numerical method based on the Runge?Kutta discontinuous Galerkin (RKDG) method is introduced in this paper, which has high-order resolution and weak correlation between cells. The bipolar charge transport under dc voltage in solid dielectrics with trapping and recombination is simulated using this new method. The results of charge profiles provided by the method are obviously different from the simulation results in the existing literature. The method was verified by problems with analytical solution and experimental observations.

Calculation of EEG problems with anisotropic conducting media by the finite volume method

A realistic head model with anisotropic conductivity is simulated by the finite volume method, which is based on the integral conservation equation. A new mesh discretization method is presented to simulate the realistic head model with anisotropic conductivity. With the method, it is convenient to calculate anisotropic problems with curved boundary surfaces, and the calculation accuracy can be enhanced. The results are compared with analytical solutions of spherical models. The comparison shows that the finite volume method is of high calculation accuracy.

A mesh generator for tetrahedral elements using Delaunay triangulation

A tetrahedral mesh generator is developed. The generator is based on the Delaunay triangulation which is implemented by using the insertion polyhedron algorithm. Some new methods for dealing with the problems associated with the three-dimensional Delaunay triangulation and the insertion polyhedron algorithm are presented: degeneracy, the crossing situation, identification of the internal elements, and internal point generation. The generator works for both convex and nonconvex domains, including those with high aspect-ratio subdomains. Some examples (electromagnetic design and semiconductor device design) illustrate the capability of the generator. >

A finite element domain decomposition combined with algebraic multigrid method for large-scale electromagnetic field computation

A nesting combination of the finite element domain decomposition method and the algebraic multigrid method is presented in this paper, which does not use the algebraic multigrid method as a pure iterative solver, but nests the iteration steps of the domain decomposition method into the iteration steps of the algebraic multigrid method. Mainly the step of updating inner boundary values in the domain decomposition iteration is nested into the transition steps of the coarse and the fine grids in algebraic multigrid method. The number of iteration between the sub-domains of the domain decomposition method can be decreased greatly by the nesting combination approach. The approach is suitable for parallel computation of large-scale problems