• Journal of the Korean Professional Engineers Association
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• v.29 no.3
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• pp.87-93
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• 1996

Lightening is a phenomenon in which electric charges accumulated in the air due to a strong ascending air current are instantly discharged. As the air current rises, the steam in the air turns into hail and grows to a certain size. Thunderclouds brought together by the ascending air current when the earth's surface is heated by strong summer sunlight produce what are called heat thunderstorms. Compared to transistors and IC's that operate at several volts, lightening induces voltages of from several 100 to several 10,000 volts and sometimes causes great damage, such as destroying equipment or delaying communication. The following describes the cause of lighting damage and basic idea behind countermeasures against such damage.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.932-934
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• 1998

In an electric substation, there are many sources of surge such as switching operations or lightning strokes. A grounding system submitted to such surge current presents very different behaviour from the observed under low frequency current. Especially, it has been reported that significant overvoltage occurs at the current feed-in point, and this may cause damages to other grounded components in the substation area. This paper describes the basic mechanism of improvement of grouding performance in transient state with auxiliary grounding grids.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.500-502
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• 2002

Receltly, Underground transmission system is getting increased. Therefore the design of grounding system becomes very important to discharge overcurrent of lightning and fault through earth and reduce sheath induced voltage and sheath circulation current. This paper describes fault current distribution ratio for grounding line with grounding types of normal joint box and sheath grounding resistor at line-to-ground fault of cable.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.175-178
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• 2004

The microstructure, electrical, and clamping voltage characteristics of ZPCCD-based varistors were investigated at sintering time of 2 and 3 h. The average grain size and density of varistor were increased from 15.2 to 19.0 and from 5.5 to 5.6 $g/cm^3$ with sintering time, respectively. The nonlinear exponent was 65.4 for 2 h and 37.4 for 3 h, and leakage current was 0.54 ${\mu}A$ for 2 h and 0.67 ${\mu}A$ for 3 h. The dissipation factor was 0.0397 for 2 h and 0.0457 for 3 h. The clamping voltage ratio at surge current($8/20{\mu}s$) of 10~300 A was increased in the range of 1.56~2.17.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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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.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1677-1678
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• 2006

전력계통의 과도현상 분석용으로 개발된 수치계산 프로그램인 EMTP (Electromagnetic Transient Program)를 사용하여 건물내에 낙뢰에 의한 뇌서지가 침입했을 때 건물 전체에 surge current가 어떻게 확산되어 가는지를 분석해 본다. 이러한 현상을 분석하기 위해서 건물의 등가회로를 $\pi$-회로로 구현하고, ANSI 규격에 맞는 뇌서지를 건물에 유입시켜서 그에 따른 건물 내부의 torrent 분포를 알아본다. 그리고, 건물 체적을 변화시켜 가면서 뇌 서지가 건물 내부의 전기기기에 미치는 영향을 해석해 본다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.4
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• pp.116-125
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• 2015

This paper presents experimental results obtained from actual installation conditions of surge protective devices (SPDs), with the aim of understanding the coordination of cascaded Class I and Class II SPDs. This paper also proposes effective methods for selecting and installing coordinating cascaded SPDs. The residual voltage of each SPD and the energy sharing of an upstream Class I tested SPD and a downstream Class II tested SPD were measured using a $10/350{\mu}s$ current wave. In coordinating a cascaded voltage-limiting SPD system, it was found that energy coordination can be achieved as long as the downstream SPD is a metal oxide varistor with a higher maximum continuous operating voltage than the upstream SPD; however, it is not the optimal condition for the voltage protection level. If the varistor voltage of the downstream SPD is equal to or lower than that of the upstream SPD, the precise voltage protection level is obtained. However, this may cause serious problems with regard to energy sharing. The coordination for energy sharing and voltage protection level is fairly achieved when the cascaded SPD system consists of two voltage-limiting SPDs separated by 3 m and with the same varistor voltage.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.57-60
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• 2005

This paper describes the experimental results of the pre-breakdown phenomena in $SF_6/CO_2$ mixtures under non-uniform electric fields caused by positive and negative lightning negative voltages. $SF_6/CO_2$ mixtures have an advantage of an environmental aspect and cost reduction, and safety aspects. In order to analyze the pre-breakdown processes in $SF_6/CO_2$ mixtures stressed by impulse voltages, pre-breakdown current and luminous signals were measured by a shunt and a photo-multiplier tube, respectively. Dielectric strengthes of $SF_6/CO_2$ mixtures were investigated. Additionally, characteristics of discharge channels were observed by high speed cameras and the physical properties were discussed. The pre-breakdown propagates with a stepwise process. The in to breakdown from the corona onset point in positive polarity was shorter than that in negative polarity. The time intervals of positive leaders are shorter than those of negative leaders, and the path of positive leader channel is zigzag.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.3
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• pp.81-87
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• 2015

In order to effectively protect electrical and electronic circuits which are extremely susceptible to lightning surges, multi-stage surge protection circuits are required. This paper presents the operational characteristics of the two-stage hybrid surge protection circuit in extra-low voltage DC power lines. The hybrid surge protective device consists of the gas discharge tube, transient voltage suppressor, and series inductor. The response characteristics of the proposed hybrid surge protective device to combination waves were investigated. As a result, the proposed two-stage surge protective device to combination wave provides the tight clamping level of less than 50V. The firing of the gas discharge tube to lightning surges depends on the de-coupling inductance and the rate-of-change of the current flowing through the transient voltage suppressor. The coordination between the upstream and downstream components of the hybrid surge protective device was satisfactorily achieved. The inductance of a de-coupler in surge protective circuits for low-voltage DC power lines, relative to a resistance, is sufficiently effective. The voltage drop and power loss due to the proposed surge protective device are ignored during normal operation of the systems.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.22-24
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• 2003

In this work, in order to investigate the effect of multiple lightning impulse currents on zinc oxide arrester blocks. We have been designed and fabricated a multi-impulse generator which can produce quintuple voltages with $1.2/50{\mu}s$ to 100kV and quintuple currents with $8/20{\mu}s$ to 12kA and we have evaluated the characteristics of zinc oxide arrester block using several electrical and physical methods after the multi-impulse test. It was found that the multi-impulse failures of ZnO arrester blocks were mainly caused by surface flashover and the multi-impulse currents test would be more suitable than single impulse current test in evaluation of the characteristics of zinc oxide arrester blocks corresponding to actual situations.