• 전기학회논문지
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• 제58권1호
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• pp.119-125
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• 2009

This paper deals with the characteristics of soil ionization affecting the dynamic performance of grounding systems under lightning impulse voltage. A concentric hemispherical electrode system was employed in order to facilitate the field calculation and analysis of the experimental results. The parameters such as the ionization threshold and breakdown field intensity, the pre-ionization and the post ionization resistances, the time-lag to ionization, the transient impedance, the equivalent ionized radius for various soil media were measured and analyzed. The dynamic characteristics of ionization processes under lightning impulse voltage are strongly dependent on the types of soil and water content. As a result, a soil ionization reduces the ground resistance and there is a little effect of applied impulse polarity on the soil ionization threshold field intensity. Although the ionization threshold field intensity of wet clay with 30% water content is the highest, its ionized zone was found to be the smallest amongst the test samples.

• Journal of Electrical Engineering and Technology
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• 제4권1호
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• pp.98-105
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• 2009

This paper presents the characteristics of soil ionization for different water contents, and the parameters associated with the dynamic properties of a simple model grounding system subject to lightning impulse currents. The laboratory experiments for this study were carried out based on factors affecting the soil resistivities. The soil resistivities are adjusted with water contents in the range from 2 to 8% by weight. A test cell with a spherical electrode buried in the middle of the hemispherical container was used. As a result, the electric field intensity $E_c$ initiating ionization is decreased with the reduction of soil resistivities. Also, as the water content increased, the pre-ionization resistance $R_1$ and the post-ionization resistance $R_2$ became lower with increasing current amplitude. The time-lag to ionization $t_1$ and the time-lag to the second current peak $t_2$ at high applied voltages were significantly shorter than those of low applied voltages. It was found that the soil ionization behaviors are highly dependent on the water content and the applied voltage amplitude.

• 전기학회논문지
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• 제65권12호
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• pp.1971-1978
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• 2016

In this paper, electrical and physical characteristics associated with the ionization growth of soil under impulse voltages in a coaxial cylindrical electrode system to simulate a horizontally-buried ground electrode were experimentally investigated. The results were summarized as follows: Transient ground resistances decreased significantly by soil ionization. The voltage-current (V-I) curves for non-ionization in soil lined up in a straight line with the nearly same slope that is the ground resistance, but they showed a 'cross-closed loop' of ${\infty}$-shape under ionization. The conventional ground resistance and equivalent soil resistivity were inversely proportional to the peak value of injected impulse currents. On the other hand, the equivalent ionization radius and time-lag to the maximum value of ionization radius were increased with increasing the incident impulse voltages. An analysis method for the transient ground resistances of the ground electrode based on the ionization phenomena was proposed. The proposed method can be applied to analyze the transient performances of grounding systems for lightning protection in power system installations.

• 전기학회논문지
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• 제66권2호
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• pp.363-369
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• 2017

This paper presents the experimental results related to soil ionization and electrical breakdown in a concentric hemispherical electrode system under lightning impulse voltages. Dynamic voltage-current and impedance-time characteristics of soil ionization were measured and analyzed. Also the electrical breakdowns of the soil gap were investigated. The time-lag to the peak current corresponds to the soil ionization propagation. The time of ionization propagation in wet sand is found to decrease with increasing the impulse currents. A drastic decrease in ground resistance was observed during the impulse current spreading in sand. The electrical breakdown appears at the wave tail of impulse voltage and results in a wide scatter in V-t curves. The voltage-current curves have a fan-like shape attributed to ionization processes which result in increasing current and decreasing voltage.

• KEPCO Journal on Electric Power and Energy
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• 제2권4호
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• pp.601-608
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• 2016

접지전극이 매설되는 토양의 전기적 특성은 지역, 계절, 환경적 요인에 따라 저항률이 다양하게 변화한다. 접지전극 주변에서의 전기적 방전현상은 매우 다르게 발생하고, 이는 접지의 성능에 큰 영향을 미친다. 접지시스템의 설계 시에 다양한 조건에서 토양의 방전 특성과 이온화 현상에 관한 분석이 필요하다. 본 연구의 목적은 토양의 이온화 현상과 과도접지임피던스의 상관관계를 파악하는데 있다. 본 논문에서는 뇌임펄스전압에 의해 접지극 주변에서 발생하는 토양의 이온화 작용과 관련된 파라미터와 과도적인 접지저항에 관한 실험적 연구결과를 기술하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1301-1302
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• 2008

The resistivity of soils around ground electrodes is changed considerably according to the factors such as soil types, water contents, grain size, temperature and pressure. In this study, ionization characteristics of different soil types containing the same amount of water content due to the impulse voltages are investigated. In order to analyze soil ionization phenomena, critical electric field intensity for ionization and pre-ionization and post-ionization resistances are measured and discussed.

• 조명전기설비학회논문지
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• 제22권12호
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• pp.87-94
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• 2008

이 논문은 뇌 임펄스전류에 의한 접지시스템의 과도적 특성에 관련된 토양의 이온화 현상과 파라미터를 기술하였다. 몇 가지 토양에서 발생하는 이온화 특성을 실험적으로 조사하였다. 절연파괴 임계전계강도와 이온화 반경을 용이하게 분석하기 위하여 원주형 실험기를 사용하였다. 전압과 전류 파형을 기초로 토양의 절연파괴 임계전계강도, 임피던스의 임펄스 전류 크기에 대한 의존성, V-I곡선과 과도임피던스를 검토하였다. 이온화 과정과 비선형 특성은 토양 종류에 매우 의존적이며, 포장용수량의 토양에서 2개의 전류피크는 나타나지 않았다. 본 연구 결과는 토양의 이온화를 고려하여 임펄스전류의 영향을 받는 접지시스템의 과도적 성능의 향상에 유용한 정보가 될 것이다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2008년도 춘계학술대회 논문집
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• pp.305-308
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• 2008

This paper presents characteristics of soil ionization when high currents such as lightning and switching surge currents are injected into a grounding rod. Soil ionization phenomena are investigated by using both voltage and current signals recorded by oscilloscope. As a result, a critical electric field intensity($E_C$) for ionization is decreased with reduction of grain size. The pre-ionization resistance($R_1$) and post-ionization resistance($R_2$) at the sand with fine grain size are getting lower with increasing current magnitude. Finally, the time to ionization($t_1$) and ionization current peak($t_2$) of fine grain size are significantly shorter than those of medium grain size.

• 조명전기설비학회논문지
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• 제23권6호
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• pp.78-84
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• 2009

본 논문은 토양의 방전 영역에서 소규모 접지전극의 과도접지임피던스의 측정결과를 제시한다. 접지전극 주변에서 이온화 특성을 사실적으르 분석하기 위해서 세 가지 형상의 접지전극을 실외에 설치하고, 고전압 임펄스 발생기를 사용하여 시험전류를 인가하였다. 정지전극에서 대지로 흐르는 전류와 응답 전압을 분석한 결과, 접지전극 주변의 이온화는 높은 대지저항률률의 토양에서 접지임피던스 감소에 기여하며 대지전위상승을 효과적으로 제한하는 것이 확인된다. 하지만 낮은 대지저항률의 토양에서는 이온화 임계전계강도가 작아서 전극 형상이 과도접지임피던스에 거의 영향을 주지 못한다. 그리고 전극형상에 따른 실험결과, 판전극보다 침부봉전극이 이온화 영역 전압범위 내에서 과도접지임피던스 저감에 보다 효과적이다.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권2호
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• pp.60-63
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• 2004

The electrical breakdown characteristics of different types of soil samples have been measured. It is shown that the threshold soil breakdown strength is affected by many factors, such as types of soil, grain size, and soil compaction. The breakdown process in the test soil samples appears to be due to air ionization in the voids between the soil particles. The results have been compared with the relevant experimental results of other researchers.