Length Of Grounding Electrode Research Articles

Evaluation principle and method of horizontal grounding electrode based on time‐varying impedance

The length of the horizontal grounding electrode is usually extended to decrease the impulse grounding resistance. In this paper, the mechanism for influencing the effective length is revealed by studying the dispersal process of a horizontal electrode and a method for determining the length is proposed. Firstly, the impulse current and the response voltage are measured at different positions. The results are used to analyse the time-varying characteristics of the impedance in the dispersal process, the mechanism and the factors influencing the effective length. Furthermore, the current propagation process is divided into a wave head process and a wave tail process. The variation rule and influencing factors of the transient impedance are determined. The wave head impedance acts as a dynamic process from the injection impedance to the wave tail impedance, and the injection impedance is not affected by the length of the grounding electrode. The wave tail impedance is constant and is equal to the DC steady-state impedance. It is proposed that the effective length is caused by two different dispersal processes and it is obtained when the tail impedance is equal to the impulse grounding resistance. These results are highly significant for optimizing the grounding device.

The Effect of Frequency Dependence of Soil Electrical Parameters on the Lightning Performance of Grounding Systems

A rigorous full-wave approach based upon the finite-element method (FEM) is used for the analysis of grounding systems taking the frequency dependence of soil electrical parameters into account. The method uses minimum approximations to model the transient behavior of grounding systems. In this analysis, frequency dependence of the soil conductivity and relative permittivity is represented using available analytical formulae obtained from experimental data. It is shown that there are cases in which the frequency dependence of the soil conductivity and relative permittivity can affect the transient behavior of grounding systems. Our simulation results show that the effect of frequency dependence is more pronounced for grounding systems buried in low conductive soils in contrast with those buried in highly conductive soils and especially when these systems are subjected to lightning subsequent return stroke currents. In practice, it seems legitimate to disregard the frequency dependence of the soil conductivity and relative permittivity for grounding systems buried in highly conductive soils subjected to lightning first return stroke currents. Within this context, it is shown that the soil conductivity, length of grounding electrode, and the frequency content of the injected current are the main factors contributing to the beneficial effect of the frequency dependence of soil electrical parameters.

Study of Lightning Safety Distance Using Rolling Sphere Method

The development of a computer program for evaluation of lightning safety distance between the tower and satellite dish is written in M-File MATLAB. The 3-dimensional illustrative graphics model is used to capture better understanding on how lightning protection system (LPS) works. The study of physical length of grounding electrode used on the tower is found to be significantly affecting the grounding system performances where they depend on magnitude of dispersed lightning strikes current and the settling time for the current to completely disperse. The grounding system performance is studied by using lightning impulse current (LIC) generator, simulated in OrCad PSpice software. It is found that the optimum length of vertical lightning rod in LPS is the same with the striking distance. There is no significant improvement is observed in lightning safety distance if the length of vertical lightning rod is higher than striking distance. The lightning strike peak current that has larger magnitude than the withstanding insulation level of specified object causes no physical damage. It is because the lightning safety distance increases when the lightning strike peak current becomes higher. It is also found that the lower grounding impedance generates higher magnitude of dispersed peak current and faster settling time.

An analysis on the Frequency-dependent grounding impedance based on the ground current dissipation of counterpoises in the two-layered soils

Abstract Because of the increased usage of power conversion equipment and their susceptibility to lightning strikes, high frequency fault currents flowing through grounding systems are increased. As grounding systems change from individual groundings to common or integrated groundings, the improved performance of grounding systems against high frequency fault currents is urgently required. When regarding the common or integrated grounding systems, most of them are required to satisfy the ground resistance defined by standards or regulations. The grounding system performance against high frequency fault currents is defined by the grounding impedance. A number of studies have reported that grounding system performance is reduced due to the increase of the grounding impedance with increasing of the frequency of fault currents. In this paper, in order to investigate the characteristics of the frequency-dependent grounding impedances of counterpoises installed in the two-layered soils, the ground current dissipation rates in each 10 m section of the counterpoises were measured and analyzed as functions of the length of grounding electrodes and the current injection point. As a result, most of the ground currents above the frequency of 100 kHz are dissipated into the earth near the current injection point and the high frequency grounding impedance of long counterpoises is converged into that of short counterpoises. The high frequency grounding impedance measured at the low soil-resistivity end of the counterpoise buried in the two-layered soils is much lower than that measured at the high soil-resistivity end.

접지전극의 길이 및 접지도선의 접속위치에 따른 접지임피던스의 주파수의존성

When lightning surges with wide frequency spectrum and power converting devices are considered, it is desirable to evaluate grounding system performance by grounding impedances. This paper presents the measured results for frequency-dependent grounding impedance for the vertical grounding electrode and counterpoise on a scale of full size. Grounding impedances of vertical grounding electrodes and counterpoises give capacitive or inductive behaviors according to the length of grounding electrodes and soil resistivity. It is inefficient to extend the length of the grounding electrode in order to decrease the ground resistance, and when designing the grounding system, the consideration of the grounding impedance should be desirable. In order to reduce the grounding impedance of counterpoise, the grounding conductors are jointed at the center of counterpoises. It is effective to reduce the grounding impedance by connecting ground rods to counterpoises in parallel.

다층 대지구조에서 수직 접지전극의 임계길이 산정

접지임피던스는 접지전극의 크기를 증가시켜도 낮아지지 않고, 토양의 특성과 주파수 조건에 따라 접지 임피던스가 최소값을 보이는 접지전극의 길이가 존재하며, 이 접지전극의 길이를 각 토양 특성과 주파수에 따른 임계길이라 한다. 본 논문에서는 대지구조의 조건을 고려하는 새로운 분포정수회로모델을 제안하였으며, 새로이 제안된 해석모델을 적용하여 MATLAB프로그램으로 수직접지전극의 임계길이와 접지임피던스를 해석하였다. 그 결과, 수직접지전극의 임계길이와 접지임피던스의 주파수의존성에 대한 대지구조의 영향이 크며, 접지시스템의 최적 설계를 위해서는 대지구조를 고려하는 것이 바람직한 것으로 밝혀졌다.

직선형 접지전극의 임계길이의 산정

뇌전류와 같이 고주파성분을 함유한 서지전류나 전자통신기기의 전자기장해를 유발하는 고주파 이상전류에 대하여 접지전극은 주파수에 의존적인 상당히 복합적인 임피던스의 특성을 보인다. 접지전극의 접지임피던스는 접지전극의 크기를 증가시켜도 낮아지지 않고, 대지의 특성과 주파수 조건에 따라 접지임피던스가 최소값을 보이는 접지전극의 길이가 존재하며, 이 접지전극의 길이를 대지의 특성과 주파수 조건에 대한 임계길이라 정의한다. 본 논문에서는 분포정수회로모델을 이용하여 수직접지전극과 수평접지전극의 임계길이를 산정하였으며, 실험결과와의 비교를 통해 타당성을 확인하였다.

Lightning Impulse Performances of Grounding Devices Covered With Low-Resistivity Materials

The low-resistivity material (LRM) is widely used to decrease the power-frequency grounding resistances of grounding devices for transmission lines in the regions with high soil resistivity. The study about the influence of the LRM on impulse performances of grounding devices cannot be found in literature. Experimental results of lightning impulse properties of grounding devices covered with LRM were presented in this paper. The influences of impulse current, geometrical dimensions of grounding devices, and soil resistivity on impulse grounding resistance and impulse coefficient of grounding devices with the LRM coverings are still the same with those without the LRM coverings. The impulse grounding resistance decreases from about 25% to 45% when the LRM covering is used. The fitting formulae to calculate the reducing ratio of impulse grounding resistance of different grounding devices are provided. On the other hand, the influence of LRM on the effective impulse length of grounding electrodes is discussed.

Effective Length of Counterpoise Wire Under Lightning Current

In a high soil resistivity area, counterpoise wires are applied to decrease the grounding resistance of tower grounding devices. If the conductor of counterpoise wire is very long, although the power frequency grounding resistance of the tower grounding device is decreased, the lightning protection performance of the transmission line is still not good. The influences of the length of grounding electrodes on the lightning transient characteristic were analyzed. The dynamic and nonlinear effect of soil ionization around the grounding electrode was considered in the analysis model of transient characteristics for the grounding electrodes under lightning impulse. The counterpoise wire has an effective length when lightning passes through it. When the length of a grounding electrode exceeds the effective length, the grounding conductor will not be utilized effectively. The simulating experiments were performed to analyze influences of the length of the counterpoise wire on the impulse characteristics. The formulae to calculate the impulse effective lengths of counterpoise wires were proposed. The model proposed in the paper has been validated by comparing the numerical results with experimental tests.

Fractal simulation of soil breakdown under lightning current

A stochastic probability model based on fractal theory is first introduced to simulate and analyze the initiation and propagation processes of the actual discharge in soil under lightning current in this paper. The influences of the length of grounding electrodes, the critical field gradient of soil breakdown and the soil resistivity on the processes of soil breakdown are discussed. And the conception of impulse effective length of grounding electrodes under impulse current is explained.

Fractal simulation of soil breakdown under lightning current

A stochastic probability model based on fractal theory is first introduced to simulate and analyze the initiation and propagation processes of the actual discharge in soil under lightning current in this paper. The influences of the length of grounding electrodes, the critical field gradient of soil breakdown and the soil resistivity on the processes of soil breakdown are discussed. And the conception of impulse effective length of grounding electrodes under impulse current is explained.