• 전기학회논문지
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• 제59권6호
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• pp.1103-1108
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• 2010

A grounding electrode has the transient grounding impedance characteristics against lightning surges. So the performance of grounding electrodes should be evaluated as a grounding impedance as well as the ground resistance. The frequency-dependent grounding impedance is varied with the shape and size of grounding electrode and is divided into both inductive and capacitive behaviors. This paper presents a theoretical analysis for the grounding impedance determined by the size of grounding electrode using the distributed parameter circuit model. EMTP and Matlab programs were used in calculating the frequency-dependent grounding impedances of vertical grounding electrodes. It was found that the frequency-dependent grounding characteristics of vertical grounding electrodes are characterized by the distributed parameters which are changed in the dimension of grounding electrodes.

• 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.

• 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.

• 대한전기학회논문지:전력기술부문A
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• 제49권6호
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• pp.289-297
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• 2000

This paper presents a comparison on the resistance and characteristics of transient response of grounding systems under surge currents using frequency domain electromagnetic field analysis software package and field test. Analysis is done by computer model, based on electromagnetic field theory approach, that accurately takes into account frequency dependent characteristics of the system. The transient performance of three grounding systems is analyzed by comparison of frequency dependent impedance and the maximal transient GPR. A double exponential lighting surge current is injected at one corner of the grounding systems. The transient GPRs a rod grounding systems are higher than mesh or electrolytic grounding systems. Af field test, the results of resistance measurement and time-variant of ground resistance slightly reduce electorlytic grounding systems less than rod and mesh grounding systems.

• 조명전기설비학회논문지
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• 제17권5호
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• pp.22-28
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• 2003

본 논문에서는 접지임피던스의 주파수 의존성에 대하여 기술하였다. 사용중인 접지시스템의 과도응답특성을 평가기법을 제안하기 위하여 가변주파수 인버터와 대역통과 필터를 사용하여 인가전류의 주파수를 가변시키면서 접지임피던스를 측정하였다. 20[Hz]∼2.1[kHz] 범위의 주파수에서 접지임피던스의 크기와 위상을 분석한 결과 접지임피던스는 인가전류의 주파수가 증가함에 따라 증가하는 경향을 나타내었다. 22.9[kV] 변전실 접지시스템에서 인가전류의 주파수가 2[kHz]일 때 측정한 접지임피던스는60[Hz]일 때 보다 거의 3배 정도 증가하였다. 접지시스템의 주파수 의존성은 접지도체의 인덕턴스에 의해 나타나는 리액턴스 성분에 기인하는 것으로 나타났다. 따라서 뇌서지 보호용 접지시스템에서는 인덕턴스를 줄이는 방향으로 접지그리드의 형태와 규모를 결정하는 것이 필수적이다.

• 전기학회논문지
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• 제67권10호
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• pp.1265-1270
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• 2018

One of the ways to improve the stability of power facilities used in power systems is to use power surge arresters and to protect against transient overvoltages and surges in normal operation. Also it is important to reduce the impact of lightning strikes because lightning can create overvoltage in the grid of the wind turbine and affect power quality. So This paper analyzes the effects of overvoltage and adjacent turbines due to single strike and multi strike to ground impedance changes when the surge arrester is deteriorated in a wind power farm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 E
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• pp.1843-1846
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• 1997

This paper describes the fault reducing effects of the 154 kV transmission tower by auxiliary grounding from the top of the tower to ground. The grounding surge impedance of the auxiliary grounding system is calculated by CDEGS(:Current Distribution Electromagnetic Interference Grounding and Soil Structure Analysis), and the critical lightning back flashover current and arcing horn dynamic characteristics are simulated by EMTP/TACS(:Electromagnetic Transient Program/Transient Analysis of Control Systems). The calculated results of total LFOR(Lightning Flashover Rate) shows that the LFOR can be reduced from 5.2(count/100km. year) to 3.4 by auxiliary grounding on the 154 kV transmission tower with one ground wire shielding system.

• 조명전기설비학회논문지
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• 제12권4호
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• pp.55-61
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• 1998

일반적으로 접지시스템에서 접지저항계산은 저주파수의 전원이 대지에 인가될 때 발새외는 대지전위상승을 측정하여 계산한다. 그러나 뇌격과 써지 엄펄스와 같은 고주파수에 해당하는 전원에 대해서는 현재의 접지 시스템에서 고려하고 있지 않기 때문에 전기설비에 매우 큰 영향을 미칠 우려가 있다. 그래서 이 논문에 서는 뇌격이 전극봉에 인가되었을 때 발생되는 접지 임피던스의 과도현상을 실험하였다. 그리고 이 실험 결과는 이론적 해석과 잘 일치하였으며 지중방전현상이 임펄스 임피던스 저감에 영향올 미친다는 사실을 확인 할 수 있었다.

• 조명전기설비학회논문지
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• 제25권8호
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• pp.106-113
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• 2011

The conventional grounding impedance of a counterpoise is calculated as a function of the length of the counterpoise by use of the distributed parameter circuit model with an application of the EMTP(Electromagnetic Transient Program). The adequacy of the distributed parameter circuit model is examined and verified by comparison of the simulated and the measured results. The conventional grounding impedance of the counterpoise is analyzed for the first short stroke and subsequent short stroke currents. As a result, the simulated results show that the minimum conventional grounding impedance gives at a specified length of the counterpoise. The shorter the time taken to reach the peak of injected currents, the shorter the length of the counterpoise having the minimum conventional grounding impedance. We also present the critical lengths of the counterpoise for short stroke currents as a function of soil resistivity. Based on these results, it is necessary to compute the length of the counterpoise in a specified soil resistivity which satisfies both the low conventional grounding impedance requirement whilst also providing a suitable ground resistance in order to obtain an economical design and installation of the counterpoise.

• 대한전기학회논문지:전력기술부문A
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• 제52권7호
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• pp.421-428
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• 2003

After the cable is installed, many geometric factors, such as bowing types of the cable and the length difference of the cable between each minor section will cause the impedance unbalance between cables. The impedance unbalance will increase or decrease the sheath circulating currents, which are critical to human safety and sustaining the capabilities of electric power. Accordingly, in this paper, a new method is also proposed to reduce the sheath circulating currents and an reduction equipment according to the theory of the new method is developed. The reduction equipment is tested when the cable is on service. The test results show that it can reduce the sheath circulating currents by up to 97.8［%］. This confirms the validation of the new method and the reduction equipment, and assures the safe operation of the transmission cables. In order to illustrate the safe operation of the cable with new current reduction equipment at transient state due to lightning and single line-to-ground fault, extensive simulations have been made. Then the protection scheme of sheath circulating currents reduction equipment is proposed by adopting the new device of RDP(Reduction Device Protector).