• 조명전기설비학회논문지
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• 제25권12호
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• pp.107-112
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• 2011

Multiple ground rods are commonly used to obtain the low ground impedance, but they will not reduce the ground impedance unless the spacings between the ground rods are sufficient. This paper presents the experimental results of frequency-dependent resultant ground impedance of two ground rods in parallel. The resultant ground impedance of two ground rods in parallel were measured as functions of the spacing and length of ground rods and the frequency of test currents and were discussed based on the potential interferences. As a consequence, the frequency-dependent ground impedance of single ground rod and two combined ground rods give capacitive. It was found that the effect of potential interference on the ground impedance is directly associated with the frequency-dependent ground impedance and is strong in low frequency. Also, in order to reduce the increasing rate of resultant ground impedance of two ground rods due to potential interference to within 10(%), two ground rods in parallel will be placed over one rod length apart.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권8호
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• pp.426-432
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• 2004

This paper presents a systematic approach of measurement, modeling and analysis of grounding system impedance in the field of lightning protection system and intelligent power equipments. The measurement and analysis system of ground impedance is based on a computer aided technique. The magnitude and phase of ground impedance were determined by the novel measurement and analysis using the revised fall-of-potential method. The ground impedances of the ground rod of 50 m long are considerably dependent on the frequency. The ground impedance is mainly resistive in the frequency range of 3-20 kHz. At higher frequencies, the reactive components of the ground impedances are no longer negligible and the inductance of the ground rod was found to be the core factor deciding the ground impedance. Although the steady-state ground resistance of the ground rod of 50 m was less than that of the ground rod of 10 m, the ground impedances of the ground rod of 50 m over the frequency range of more than 60 kHz were much greater than those of the ground rod of 10 m. Furthermore, the equivalent circuit model based on the measured data was proposed. and the calculated results were in approximately agreement with the measured data.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1470-1471
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• 2007

The mutual coupling between the current and potential measuring wires makes serious effect on the measurement of the ground impedance. For analyzing the effect of mutual coupling, we compared the ground impedance measured on site with the ground impedance calculated with MATLAB. When the parallel length is 10 [m], the measured ground impedance is similar with the calculated ground impedance. As the parallel length is extended over 10 [m], the error between measured ground impedance and calculated ground impedance is also increased on a large scale. We analyzed the mutual coupling by the frequency and present the inaccuracy of ground impedance quantitatively.

• 조명전기설비학회논문지
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• 제26권2호
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• pp.99-105
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• 2012

This paper deals with the experimental results of the frequency-dependent resultant ground impedance of vertical ground electrodes installed with a regular n-polygon. In order to propose an effective method of installing the vertically-driven multiple ground electrodes used to obtain the low ground impedance, the resultant ground impedance of ground electrodes installed with a regular n-polygon were measured as functions of the number of ground electrodes and the frequency of test currents and the results were discussed based on the potential interferences among ground electrodes. As a consequence, the effect of potential interference on the resultant ground impedance of vertical ground electrodes is frequency-dependent and it is significant in the low frequency of a few hundreds [Hz]. The resultant ground impedance of multiple vertical ground electrodes is not decreased in linearly proportion to the number of ground electrodes due to the overlapped potential interferences. Also the distributed-parameter circuit model considering the potential interference, the frequency-dependent relative permittivity and resistivity of soil was proposed. The simulated results of the frequency-dependent resultant ground impedance of multiple vertical ground electrodes are in good agreement with the measured data.

• 조명전기설비학회논문지
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• 제28권5호
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• pp.98-105
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• 2014

Soil discharges near the ground rod play an important role to reduce the ground potential rise and the ground impedance and to help the fault current to spread into the earth. This paper presents the effects of soil discharges on the transient and conventional ground impedances when the lightning impulse voltage was applied to a ground rod with radial needles. The current-voltage (I-V)curves and transient ground impedance curves were calculated based on the measured current and potential traces. Soil discharge behaviors related to I-V curves and transient ground impedance curves were analyzed as a function of the magnitude of lightning impulse voltages. As a result, the soil discharges occurred near the ground electrode contribute to the reduction of conventional ground impedance and limits the ground potential rise effectively under lightning impulse voltages.

• 조명전기설비학회논문지
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• 제27권3호
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• pp.36-42
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• 2013

This paper deals with the frequency-dependent ground impedance of ground grids combined with the carbon ground electrodes. Ground grids are generally valid for multipurpose grounding systems as well as lightning protection systems. The carbon ground electrodes may be supplementarily used to reduce the high frequency ground impedance and to improve the transient response to surge currents. The frequency-dependent ground impedances of ground grids combined with or without the carbon ground electrodes were measured and their simulations with due regard to frequency-dependent soil resistivity were implemented by using EMTP program and Matlab modeling. As a consequence, the ground impedance of ground grids combined with the carbon ground electrodes is significantly reduced when the test current is injected at the terminal of the carbon ground electrode. The measured and simulated data for the test ground grids fairly agree with each other. It was found that the proposed method of simulating the frequency-dependent ground impedance is distinguished. The simulation techniques of predicting accurately the ground impedances without actual measurements can be used in the design of grounding systems based on ground grids and the carbon ground electrodes.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2007년도 추계학술대회 논문집
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• pp.231-234
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• 2007

This paper presents an analysis method of transient ground impedance using the lightning impulse and variable frequency currents. The transient ground impedance strongly depends on the configuration and size of grounding electrodes and the shapes of impulse currents, and the inductance of grounding electrodes has a significant affect on the transient impedance of the grounding system. There are some differences between the effective impulse ground impedance which was introduced some papers and the transient ground impedance. The transient ground impedance measured from the peak value of impulse voltage and the peak value of impulse current is more reliable than the effective impulse ground impedance.

• 전기학회논문지
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• 제58권9호
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• pp.1778-1783
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• 2009

Ground impedance for the large grounding system is measured according to the IEEE Standard 81.2 which is based on the revised fall-of-potential method of installing auxiliary electrode at a right angle. When the auxiliary electrodes are located at an angle of $90^{\circ}$, the ground impedance inevitably includes the error due to earth mutual resistance. In this paper, in order to accurately measure the ground impedance of vertically-driven ground electrodes, error rates due to earth mutual resistance are evaluated by ground resistance and ground impedance measuring devices and compared with calculated values. As a result, the measured results are in good agreement with the computed results considering soil layer with different resistivity. The error rates due to earth mutual resistance decrease with increasing the length of ground electrode in the case that the ratio of the distance between the ground rod to be measured and the auxiliary electrodes to the length of ground electrode(D/L) is same. The ground impedance should be measured at the minimum distance between the auxiliary electrodes that will have an estimated measurement accuracy due to earth mutual resistance.

• 조명전기설비학회논문지
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• 제25권12호
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• pp.88-93
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• 2011

When the ground current is injected into the adjacent ground electrode, the potential interference is caused between ground electrodes, the ground potential interferences have been largely studied with power frequency fault currents. Many attempts to find the frequency-dependent grounding impedance report that the high frequency grounding impedance is very different with the ground resistance. This paper presents experimental data on the frequency-dependent potential interference effects in the vicinity of ground rod. The ground potential rises around the test ground rod of 4 or 6[m] were measured and discussed. As a result, the ground potential rises and potential interference factor are decreased with decreasing the grounding impedance. It was found that the lowering of grounding impedance is critical to reduce the ground potential interference effects.

• 조명전기설비학회논문지
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• 제22권6호
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• pp.100-108
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• 2008

접지전극의 형태, 크기, 재질 및 임펄스전류의 형상에 따라 변화하는 과도접지임피던스는 접지시스템의 성능에 중요한 영향을 미친다. 본 논문은 기존의 실효임펄스임피던스가 실제 과도접지임피던스를 얼마나 효과적으로 나타내고 있는가에 대한 분석과 보다 효과적인 과도접지임피던스 평가방법에 대하여 실험적인 결과를 제시하였다. 실험에 사용된 접지전극은 저항성분과 인덕턴스를 포함한 모의 접지전극과 1[m] 탄소접지봉, 9[m] 일반동봉 그리고 40[m] 매설지선이며, 가변주파수 전류와 임펄스전류에 의한 접지임피던스를 각각 측정하였다. 각각의 값을 비교 했을 때 기존의 실효임펄스임피던스의 값보다는 전압의 최대 값과 전류의 최대 값을 이용하여 과도접지임피던스를 구한 임피던스 값($Z_1$)이 등가주파수에 해당하는 가변주파수 전류에 의해 구해진 접지임피던스에 근접함을 확인하였다.