Search

Based on the method of moment (MOM), a new method is developed to evaluate the electromagnetic shielding effectiveness of the rectangular metal enclosure with aperture covered with wire grid. The wire grid is modeled as thin wire, and the currents on the wire segments, which are taken as unknowns, are modeled by triangular basic functions. In order to expand the unknown electric currents on the surface of the cavity, Rao--Wilton--Glisson (RWG) basic functions are used on the surface patches to model the concerned objects. In terms of the continuity of the tangential electric fields on the surface of conductive plane and thin wire, a set of equations can be established. From the equations set, the currents on the surface patches and wire grids can be obtained. The accurate shielding effectiveness of the rectangular enclosure of metal structure with apertures covered with wire grid can be determined. By comparing the calculation with measurement results, the method is validated. Finally, the shielding performance of a protection cell in a practical substation is analyzed as an application. Index Terms--Apertures, electromagnetic shielding, moment methods, numerical analysis.

In this paper, the shielding performance of reinforced concrete construction is analyzed employing the method of moments (MoM) and equivalent principle. The surface of the reinforced concrete are modeled using rectangular surfaces patches. The surface of the reinforced concrete is assumed as metallized and modeled based on the equivalent principle, and the proposed technique has fewer unknown variables than the MoM volume integral equation solution and is quicker in computation and more applicable to analyze the shielding performance of reinforced concrete building with complex structure. The comparison between the calculation results of this paper and FDTD shows that the method is effective, and the shielding effectiveness of a real building in substation is analyzed at last. Index Terms--Electromagnetic shielding, frequency domain analysis, moment methods, numerical analysis.

The corona generated from high-voltage direct-current transmission lines can induce the ion around the lines, which will increase the electric field and the ion current density and influence the environment nearby. Based on the finite-element method, an iterative algorithm to analyze the electric field and the ion current density at the ground level generated from the bundled conductors of bipolar fines is proposed. After the validity of the method is testified, some examples are analyzed. The method has been used to design [+ or -] 800 kV transmission lines system in China. Index Terms--Electric field, high-voltage direct-current (HVDC), ion current density, power lines.

Based on finite-element method (FEM) of 1-D conductor element coupled with 3-D soil element, we take into account the frequency dependent characteristic of the discretized elements to analyze the grounding performance of the substation grounding grids. Compared with A-V formulation of 3-D FEM, the proposed method can greatly save the CPU time, and the frequency can be considered during FEM modeling. In comparison with the method of moment (MoM) and the measured results, the presented method is proved to be correct and effective. Furthermore, we can calculate the H-field generated by the substation grounding grids with both currents in the underground conductors and leakage currents flowing in the soil. The results show slight difference between FEM and MoM, which can be explained by the fact that the leakage currents in the soil are not taken into account for MoM. Index Terms--Finite-element method (FEM), frequency domain method, method of moment (MoM), substation grounding grids.

An improved subcell model is presented for including thin material sheets method in the finite-difference time-domain (FDTD) method. This improved subcell can be used to simulate a thin magnetic ([[micro].sub.s] [not equal to] [[micro].sub.o]) sheet. Then, the improved subcell model is applied to the analysis of the shielding effectiveness (SE) of the electromagnetic wave propagating through a thin infinite material sheet, which is verified by comparison with the analytical results. Updated equations for components of the field on special spatial grids which are on edges and corners of the enclosure are presented, and the subcell model is used for the analysis of a thin-walled enclosure with an aperture. The FDTD results are in very good agreement with the test results. Index Terms--Enclosure with an aperture, shielding effectiveness (SE), subcell model, thin material sheet.

An improved subcell model is presented for including thin sheets in the finite-difference time-domain (FDTD) method. This improved subcell model can simulate thin multilayer material sheets and was verified by comparison with the analytical results for the analysis of shielding effectiveness (SE) of the electromagnetic wave through a thin multilayer sheet. Then, the subcell model was used for the analysis of SE of a multilayer thin-walled enclosure with an aperture. The FDTD results were in very good agreement with the test results. Finally, the electromagnetic wave penetration through a wall of an enclosure and the electromagnetic wave coupling through an aperture of enclosure were compared. Index Terms--Enclosure with aperture, improved subcell model, shielding effectiveness (SE), thin multilayer sheet.

Electromagnetic interference (EMI) on secondary dc cable in cable tunnel due to a direct lightning strike in substation threatens the safe operation of electronic equipment and system connected to the cable. In order to reduce EMI, the cable shield is generally connected to the grounding grid at both ends. Ground potential difference between two grounding points of the cable shield can be high due to high impedance of the grounding grid at high frequencies. In this paper, we present a hybrid method to analyze this complex system. As a result, both the current flowing in the cable shield and the transverse voltage between the cable core and shield are calculated. Compared with the measured results, the proposed method is demonstrated to be correct and effective. Index Terms--Electromagnetic interference (EMI), grounding grid in substation, lightning, secondary cable.

In order to research the transient current and voltage along the busbar in substations, the ground return impedance of aerial multiconductor transmission lines above a multilayer soil is researched and its time-domain expression is obtained by using vector fitting method. After the algorithm is testified, the effect of the multilayer soil is included in the finite-difference time-domain method based on recursive convolution. The proposed method is demonstrated to give the same results as the famous software EMTP, and to have a little difference from the results of method of moment. Finally, some examples in substations are analyzed to illustrate the effect of the soil on the transient. Index Terms--Aerial multiconductor transmission lines (MTLs), finite-difference time-domain (FDTD), substation, transient.

When dc current is injected into the earth through the grounding electrodes of a high-voltage direct current (HVDC) system, transformers in ac system may be under dc bias if the dc currents flowing through the transformers are large enough. In this paper, a numerical method coupling the method of moments (MOM) to circuit equations is presented to calculate the dc current distribution in ac power system caused by an HVDC system. The MoM is used to calculate the electric fields in complex earth structure caused by all the grounding systems including the dc grounding electrodes, the ac substation grounding systems and the long metal pipe lines. The circuit equations are coupled to the moment method to take account of the effects of the transmission lines. By using the method, the dc current distribution in an ac power system caused by an HVDC system is analyzed. Some useful conclusions are drawn from the analyzed results. Index Terms--Current distribution, grounding electrodes, high-voltage direct current (HVDC) transmission, method of moments (MOM).

An approach coupling indirect boundary element method with charge simulation method to calculate the electric fields around the head of transmission tower and its composite insulators is presented. On the composite insulators, the indirect boundary element method is used, while on the transmission tower and the transmission lines, the charge simulation method is used. Therefore, both the heterogeneous medium such as the composite insulators and the filament metal structure such as the transmission tower and the transmission lines are considered all together. The electric field distribution around a 330-kV transmission tower and its composite insulators was analyzed. The method gives the possibility to model very complex geometries. Index Terms--Boundary element method (BEM), charge simulation method (CSM), electric fields, insulators.

A method of moments solution for analyzing the electromagnetic shielding properties of rectangular metal enclosures with apertures over a lossy half space which can model the ground is presented. The objects are modeled by rectangular surface patches. The roof-top basic functions are used to expand the unknown electric and magnetic currents on the surfaces of the cavity and the apertures. An effective method based on the generalized pencil-of-function (GPOF) method is developed to calculate the generalized Sommerfeld integral (GSI). With this method, the value of Greens' function can be obtained quickly and accurately. Validation of the method is presented by comparing the calculation results with the results obtained by measurement. Finally, the method is successfully applied to calculating the shielding effectiveness of a relay cell in a substation. Index Terms--Absorbing media, apertures, electromagnetic shielding, numerical analysis.

Soil ionization has a great effect on the performance of grounding electrodes fed by currents of high magnitude. In this paper, a numerical method is proposed to analyze the transient performance of grounding system, which takes account of the dynamic and nonlinear effects of soil ionization. The method couples moment method with circuit theory and Fourier transform. The transient performance of grounding system considering the soil ionization effect is compared with that not considering soil ionization effect. Index Terms--Grounding, ionization, iterative methods, transient analysis.

Based on multiconductor transmission lines (MTLs) and the antenna method, a hybrid method is proposed to analyze the transient electromagnetic fields due to the operation of switches in substations. The method is valid in either near or far field. At first, the wave process along the busbars is calculated by using the finite-difference time-domain method. Then the field is calculated by using electrical dipole theory. In order to take the effect of lossy soil into consideration with reason, the closed-form of the generalized Sommerfeld integral is calculated by using generalized pencil-of-function and an equation derived from the Sommerfeld identity, which saves much time. After a model of busbars in a 500-kV substation is set up, the transient electromagnetic field is predicated. Index Terms--Electromagnetic field, FDTD methods, substations, transient analysis.

According to the Method of Moment, a new method to analyze the grid fed by harmonic currents is presented. The method can be used to the condition that the grid is in at least ten-layer soil with a frequency of the injected currents up to 1 MHz. There can be more than one injected current, and the grounding conductor of the grid can be put in any form. Validation of the method is presented by comparing it with other existing methods. As an application of the presented method, breaks in the substation's grounding grid are diagnosed by the measured voltages on the surface of the ground. Index Terms--Diagnosis, electromagnetic fields, grounding, nonhomogeneous media.

An adaptive technique of calculating three-dimensional eddy currents by using the three-component boundary element algorithm is presented. The three-component algorithm is a minimum-order boundary element method in the calculation of three-dimensional eddy currents, which employs only three scalar unknowns on each mesh node, so that about 40% computer memory and 50% computational time can be saved relative to the conventional four-component algorithm that usually employs a scalar and a three-component vector as unknowns. The error estimate of the three-component algorithm and the implementation of the adaptive technique are described. The error estimate is based on the residue of the boundary element equation at the non-collocation mesh nodes. The adaptive technique is able to save the computer memory and increase the accuracy of the solution greatly.

For improving insulated level of 220 kV load-ratio voltage power transformer, two-dimensional and three-dimensional electric fields around the shielding ring of the regulative winding in this transformer have been precisely calculated by the finite element method. The calculated results show that the field intensity at the oil-corner for the shielding ring with the traditional oil-corner design is too high to insure enough insulated level of this transformer. Two new shielding ring structures without oil-corner have been designed by using the finite element method. The maximum field intensity for each new design is reduced to 2,000 kV/mm from 2.633 kV/mm under 100 kV applied voltage.

In order to analyze the switching transient electromagnetic field generated by the aerial busbars in substation, the transient wave process of the lossy aerial multi-conductor transmission lines (MTLs) with branch is calculated by using the finite- difference time-domain (FDTD) method. Based on the Pade approximation and on Prony's method, the iterative equations of the lossy aerial MTLs with branch are presented in this paper. An aerial busbars model in a 500 kV substation is analyzed when circuit breakers and disconnect switches are closed. The results can be used to research the immunity of the control devices in the substation. Index Terms--FDTD, MTLs, substation, wave propagation.

Presents a formula of partial derivatives of the percent impedance to the widths of the leakage magnetic channels in a shell-form power transformer based on the computation of magnetic field forces subjected on current coils. Magnetic field computation; Calculation of partial derivatives; Procedure of automatic design; Conclusions.