Transient Grounding Resistance Research Articles

A Novel Lightning Strike Response Simulation Method for Transmission Lines Considering Transient Grounding Resistance

A Novel Lightning Strike Response Simulation Method for Transmission Lines Considering Transient Grounding Resistance

Surge analysis on wind farm considering lightning strike to multi-blade

The protection of the wind turbines is one of the significant problems, especially as lightning strikes the blades. In this paper, the authors bring forward a model in which nine interconnected wind turbines are connected to the infinitive bus by underground cables. When the blades are struck, for detailed investigation, all the cables inside the wind turbine and underground cables, tower, blades, and other equipment of wind turbine need to be designed in transient mode. Accordingly, the grounding system is also considered by the time-domain model, in which transient grounding resistance behavior is based upon the frequency-dependent model. For this purpose, the EMTP.rv is employed to study the transient behavior of the wind farm when the blades are struck. Eventually, by studying the residual voltage and discharged current in medium voltage surge arrester (MVSA) when lightning strikes WT, the energy absorbed by the MVSA is calculated and employed to evaluate the wind farm resilience against a different type of lightning. As a result, a new approach can be advised for the protection of wind farms against lightning by investigating the energy absorbed by MVSA.

The research to reduce the transient grounding resistance of communication protection system with resistance matching method

In this paper, we study reducing the transient grounding resistance (TGR) of communication protection system with resistance matching method. We set single or double matching layers surround the grounding rod and change their sizes and conductivity to get the laws about reducing the TGR peak and stable value. The finite-difference time-domain (FDTD) method is adopted for calculating. For the single matching layer, both of the peak and stable value of the vertical grounding rod TGR reduce, compared with normal case, as matching layer exists when the conductivity of matching layer is larger than that of ground. For the double matching layers, the TGR value will reduce even more than single matching layer case when the conductivity of outer matching layer is larger than that of ground.

Inverse Laplace Transform of the Ground Impedance Matrix of Overhead Lines

This letter deals with the calculation in time domain of the transient ground resistance matrix of an overhead transmission line (TL). Each element of the matrix is evaluated by solving analytically the inverse Laplace transform of the general integral expressions of the ground impedance in frequency domain proposed by Sunde. The presented expressions are suitable for the direct implementation in an electromagnetic transient program (e.g., EMTP-like ones) based on a time domain solution of the TL's equations.

An improved method for expressing the transient ground resistance of overhead transmission lines by exponential polynomial

In this study, a method is proposed for expressing the transient ground resistance of the overhead transmission lines (TLs) by the exponential polynomial. The relation of the poles due to the rational approximation of the ground resistance between the ground conductivity, permittivity and the line geometry is fully discussed. A concept of ‘normalise poles’ is introduced, which makes it very easy to evaluate the poles according to any ground conductivity, permittivity and line geometrical geometry. A new and easily programmed method is achieved which can overcome the uncertain error caused by the conventional vector fitting method when approximating the ground resistance. Based on this method, a recursive convolution can be achieved for analysing the multi-conductor TLs system, so good efficiency can be obtained. Several examples are provided to demonstrate the validation of the proposed method for evaluating the transient ground resistance with different ground parameters and line geometry, and an application on calculating the lightning induced voltages of the overhead TLs system is also provided.

New Integral Formulas for the Elements of the Transient Ground Resistance Matrix of Multiconductor Lines

This paper proposes new formulas for the calculation of the transient ground resistance matrix elements based on the analytical solution of the inverse Laplace transform of the Sunde's logarithmic equation. The new formulas solve the computational issues in the representation of the transition between early time and late time response of the line that arises when adopting the expressions already available in the literature. The formulas are adopted for the calculation of the per-unit length voltage drop due to the transient ground resistance in a multiconductor overhead line and the results match those provided by the numerical inverse Fourier transform of Sunde's logarithmic equation.

An Improved Approach for the Calculation of the Transient Ground Resistance Matrix of Multiconductor Lines

The general integral expressions for the elements of the ground impedance matrix do not have an analytical inverse transform in the time domain. Therefore, the ground transient resistance of a multiconductor line is commonly evaluated in the time domain by means of approximated expressions in order to avoid the numerical inverse fast Fourier transform burden. In this paper, we propose a new analytical approach for calculating the transient ground resistance in the time domain that stands on the very accurate Sunde logarithmic expression for the ground impedance matrix of an overhead multiconductor line. The proposed analytical approach is adopted for calculating lightning induced voltages in a multiconductor overhead line. The results show that the proposed analytical formula is in perfect agreement with the numerical inverse Fourier transform of the general Sunde expression and, therefore, is more accurate than the approximated expressions available in the literature.

Ground Transient Resistance of Underground Cables

During transients involving multiconductor lines, the importance of the ground finite conductivity is well known and various techniques and expressions have been presented in literature for the inclusion of its contribution into the per unit length parameters. The direct time domain approach based on the introduction of the transient parameters and on the numerical solution of the telegrapher's equations demonstrated to be accurate and efficient for the analysis of typical transients. In this letter, the expressions for the ground transient resistance for underground cables, based on the closed-form inverse Laplace transform of the classical Pollaczek expressions (valid for the low-frequency-range), are presented and discussed.

FDTD Calculation of Transient Electromagnetic Fields in the Grounding System of Wind Towers Due to Direct Lightning Strikes

Lightning protection system (LPS) for wind power generation has become an important public issue due to greatly increasing installations of wind turbines (WTs) worldwide. Grounding system is one of the most important components required for appropriate LPS for WTs. Although the finite-difference time-domain (FDTD) method for solving Maxwells equations is difficult for computing earth potential rise (EPR) and transient grounding resistance (TGR), this method is used in this paper to compute EPR and TGR for different configurations of the grounding system of WTs because FDTD method can efficiently deal with the three-dimensional geometrical configurations of an investigated structure unlike electromagnetic transient programs (EMTP).

Time-Domain Analysis and Experimental Verification of Portable Grounding System’s TGR

The portable grounding system plays an important role in the lightning protection system of mobile equipments. But the traditional earth electrodes composed of vertical rods wouldn’t work well or would take a long time to set up in some conditions such as frozen soil, hard clay and so on. In this paper, a new type of portable grounding system which can be quickly spread and folded has been designed. To analyze the TGR’s (Transient Grounding Resistance) time-domain characteristics, the grounding systems have been modeled and simulated with FDTD (Finite Difference Time Domain). The influence rule of electrodes’ number and down-lead’s position to TGR has been studied with numerical analysis and validated with experiments. The results show that the new grounding system works well even on cement floor.

Experiments and Analyses of Horizontal Earth Electrodes’ TGR on Various Grounds

In this paper, a new type of portable horizontal grid earth electrode has been designed for mobile equipments. With the impulse ground measurement system, the responses to double exponential pulse current of five earth electrodes in two arrangements have been tested on soil, grassplot and cement floor respectively. After filtering and calculating, the curve of transient grounding resistance (TGR) in time domain can be gotten. And in the end, some conclusions have been drawn. The analysis of discharging capacity of horizontal grid earth electrodes in time domain has great significance in the design of mobile equipments’ earth devices.

Optimized Programs for Shaped Conductive Backfill Material of Grounding Systems Based on the FDTD Simulations

A new transient grounding resistance calculation model is proposed for the finite-difference time-domain (FDTD) method. In FDTD, the perfectly matched layer is backed by the perfect electric conductor (PEC) wall. By stretching the grounding system lifting line to the PEC wall, the grounding system performance is simulated. With this model, a 2-D cylindrical coordinate domain FDTD simulation was carried out to study cylindrically shaped conductive backfill material (SCBM) performance with fine grids. From experimental results, some optimal programs have been derived for SCBM in grounding systems. It is found that a large metal rod size can reduce the SCBM resistance only when the main body conductivity is low, and the reduction effect declines as the conductivity increases. Second, the SCBM resistance is as low as the resistance of a conductor of the same size when the main body conductivity reaches 0.5 S/m. Third, enlarging the SCBM radius can reduce the grounding resistance, and resistance can also be reduced by enlarging the SCBM length when it is less than its effective length. Fourth, the grounding resistance of an SCBM, whose conductivity is linear or parabolic type varied, can be as low as that of a totally high conductivity SCBM.

The Effect of Grounding Electrode Parameters on Soil Ionization and Transient Grounding Resistance Using Electromagnetic Field Approach

The soil ionization phenomenon occurs during the dispersion of lightning current into the earth. This phenomenon causes the grounding electrode resistance to be effectively reduced. The extension of the soil ionization depends on the current amplitude along the electrode and the resultant electric field intensity surrounding the electrode. The electrical and physical parameters of the grounding electrode system are found as factors that affect the electric field intensity. In this study the electromagnetic field approach and the soil breakdown theory are taken into account to investigate the effect of the mentioned factors on soil ionization and grounding resistance. Changing the parameters of the grounding electrode system affect the electric field distribution around the electrode. Based on the conditions the grounding electrode resistance was reduced between 12% to 75% by considering the soil ionization effect.

An Algorithm for the FDTD Modeling of Flat Electrodes in Grounding Systems

A sub-cell algorithm for the finite-difference time-domain (FDTD) modeling of flat electrode in grounding systems is proposed. The electromagnetic field variation near a flat electrode is derived from the integral of the differential electric field which is radiated by the distributed charge on an electrostatic charged flat electrode. By fully incasing the field singularity into the coarse cells containing the electrode with the Faraday's Law, a sub-cell algorithm has been proposed to reduce computational resources when modeling the flat electrode. The accuracy of the derived field singularity is verified from comparison with the field given by the high-resolution standard FDTD simulation. The efficiency of the proposed algorithm has been approved by verifying the transient grounding resistance (TGR) of the grounding system using the proposed algorithm and the computational memory and time usage.

A New Derivation of TGR with Naked Antenna in Lossy Medium

A new derivation of Transient Grounding Resistance (TGR) has been proposed in this paper. Take grounding system as naked antenna in lossy medium, and then get the input resistance of naked antenna in a given frequency based on Helen current integral equations. With inverse Fourier transform, the resistance calculation equations can be translated from frequency domain to time domain. The result can be applied to design a new grounding system and to calculate its TGR .

The Analysis of Transient Grounding Resistance of Portable Horizontal Grid Earth Electrodes

Based on current situation of mobile equipments earth devices, a new type of portable horizontal grid earth electrode has been designed. With the impulse ground measurement system, different number of earth electrodes responses to double exponential pulse current have been tested on cement grounds. Impulse waves of voltage and current have been gotten by experiments, and the curve of Transient Grounding Resistance (TGR) can be calculated. The analysis of discharging capacity of horizontal grid earth electrodes in time domain has great significance in the design of mobile equipments earth devices.

OPTIMAL PROGRAMS TO REDUCE THE RESISTANCE OF GROUNDING SYSTEMS

In this paper, some optimal programs have been proposed through the analyses of transient grounding resistance (TGR) to reduce the grounding resistance using the flnite-difierence time-domain method. First, the TGR of various electrode types, lengths and sectional programs is studied, and it is found that a ∞at bar is the most flnancially e-cient conductor to be used as grounding electrode. Enlarging grounding electrode length can reduce grounding resistance when it is shorter than the efiective length, but the reduction efiect declines as the length increases. Additionally, a series of small electrodes would lead to a much lower resistance than a single large one. Second, it is demonstrated that locally improving the soil near the grounding system is an e-cient way of reducing the grounding resistance. Improving a limited area soil surrounding the lifting line would reduce the peak resistance signiflcantly, while local enlarging electrodes surrounded soil conductivity can reduce the grounding system steady resistance obviously.

AN EFFICIENT METHOD TO REDUCE THE PEAK TRANSIENT GROUDNING RESISTANCE VALUE OF A GROUNDING SYSTEM

In this paper, an e-cient method is proposed to reduce the peak transient grounding resistance (P-TGR) of a grounding system. By surrounding the lifting line with a material volume, the P-TGR of the grounding system is greatly reduced. The efiect of the surrounding volume conductivity and relative permittivity on the P-TGR is also tested. Second, the rectangular surrounding material volume is shielded with a metallic pipe to reduce the P-TGR further. Third, the shielding metallic pipe is connected to the grounding electrode with thin wire, and the efiect of the number of the wires on the P-TGR is also analyzed. It is demonstrated that the P-TGR of the grounding system has been reduced signiflcantly.

TRANSIENT RESISTANCE ANALYSIS OF LARGE GROUNDING SYSTEMS USING THE FDTD METHOD

In this work, a new method has been proposed for the flnite-difierence time-domain (FDTD) analysis of the transient grounding resistance (TGR) of large grounding systems. To calculate the TGR, a coarse grid is occupied to model the earthing conductor, the convolution PML (CPML) is chose to truncate the computational domain, and the parallel implementation is involved to overcome the memory limit of the serial FDTD. With this model, the efiect of the earthing conductor number and topology structure, the buried depth, and the ground permittivity and conductivity on the TGR is tested to flnd an optimized program to decrease the TGR of the lightning protection grounding systems.

FDTD Modeling of the Earthing Conductor in the Transient Grounding Resistance Analysis

The grounding system plays an important part in the lightning protection system of power and communication systems. The finite-difference time-domain (FDTD) method is widely used in modeling complex electromagnetic interaction problems. However, it is difficult to model the earthing conductor using the standard FDTD method in the transient grounding resistance (TGR) analysis for the electrically small depth of the earthing conductors. In this letter, a new method has been proposed to model the earthing conductor by incorporating the singularities of the field variation near the conductor into the Faraday's contour path. The efficiency of the proposed model has been approved by verifying both the supposed field distribution near the earthing conductor and the TGR.