• 한국지구과학회지
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• 제31권7호
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• pp.749-761
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• 2010

본 연구에서는 2006-2007년 여름(6-8월)동안의 기상청 낙뢰 관측자료와 자동관측소 강우량 자료를 사용하여 여름철 낙뢰와 강우의 관계에 대해 분석하였다. 대부분의 부극성 낙뢰는 대류가 활발한 중심에 집중되어 발생하고 낙뢰빈도가 높고 강한 강우를 동반하였다. 반면 대부분의 정극성 낙뢰는 구름의 가장자리 또는 모루운에서 발생하고 낙뢰빈도는 낮으며, 약한 강우를 동반하였다. 일반적으로 강우강도는 부극성과 정극성이 함께 발생했을 경우 가장 강하고 부극성 낙뢰, 정극성 낙뢰, 그리고 낙뢰가 발생하지 않은 순으로 나타나고 있다. 여름철 전체 낙뢰 중 정극성 낙뢰의 비율은 평균 10% 이하이며 강우를 유발하지 않는 낙뢰의 비율은 평균 34%이다. 강우강도는 특히 부극성 낙뢰빈도와 높은양의 상관을 보였고, 낙뢰는 강우와 동시에 발생하거나 약 10분정도 선행하는 경향을 보였다. 낙뢰를 동반한 강우를 대류성 강우로 정의하여 분석한 결과 우리나라 여름철 강우 중 적어도 20% 이상은 대류성 강우이며 6, 7월보다는 8월에 대류성 강우가 많이 발생하고 있다. 또한 강우 및 낙뢰와 같이 대류성 강우의 비율도 오후에 최대치를 보이는 일변동을 보인다.

• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.662-669
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• 2014

Mineral oil has been widely used as dielectric insulating fluid in transformers due to its excellent performance in-service. However, there are few issues with mineral oil such as it has poor biodegradability and could contaminate the environment if a spillage occurs. With the increasing tight regulation on safety and environment, alternative fluids for mineral oil are currently being investigated and among the suitable candidate is the vegetable oil. There are different types of vegetable oils and one of them is the palm based oil. At the moment, extensive research works are carried out to examine its feasibility to be applied in transformers. This paper will review the previous research works that were carried out to examine the suitability of palm based oil as dielectric insulating fluid in transformers. The physical and chemical properties of palm based oil are studied based on viscosity, acidity, oxidation stability and flash point. Next, the electrical characteristics of palm based oil are examined based on AC breakdown voltage, relative permittivity, dissipation factor and partial discharge.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1635-1637
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• 2003

송전선의 뇌사고율은 뇌방전 현상, 송전선의 써지 전달 현상, 아킹혼 사이의 섬락 현상 등 다양한 현상이 관련된다. 송전선의 내뢰설계 목표는 이러한 자연현상 및 물리적인 현상이 편차를 포함하고 있다는 것을 인식하고, 가능한 한 정확도가 높은 뇌사고율을 예측을 수행하고 허용 가능한 뇌사고율을 산정하여 송전선로 설계시 반영하는 것이다. 이러한 예측 계산을 위해 한전에서는 EPRI에서 개발한 FLASH 프로그램을 기본으로 사용해 왔으며, 이 예측계산법의 타당성은 예측 사고율과 사고 실적과의 비교에 의해 검토되어야 한다. 한전에서는 과거 10년간의 뇌사고 실적과 FLASH 프로그램으로 계산한 예측 사고율이 차이가 많이 나타나고 있어, FLASH 프로그램의 예측 계산법의 타당성에 의문을 제기하고 있는 상황이다. 일본 전력회사들은 뇌사고율을 예측 계산하기 위하여 1988년에 전력중앙연구소에서 개발한 프로그램을 사용하여 왔으며, 최근에 사고 실적과의 비교 및 관련 연구를 수행하여 예측 계산 프로그램에 사용되는 파라메타를 수정 보완한 LORP2000-1을 완성하였다. 본 논문에서는 지리, 기후적으로 한국과 유사한 일본의 자연현상을 반영한 LORP 프로그램의 예측계산법이 한전 송전선로의 뇌사고율 예측 계산에 적용 가능성을 사고 실적과의 비교를 통해 검토하였다.

• 조명전기설비학회논문지
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• 제20권2호
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• pp.81-88
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• 2006

본 연구에서는 뇌방전의 전기적 특성에 대해 파악하고자 전계 및 자계 측정시스템을 구축하였다. 주파수 대역 및 응답감도는 전계측정시스템 $40[Hz]{\sim}2.6[MHz]$, 2.1[(V/m)/mV], 자계 측정시스템 $300[Hz]{\sim}1[MHz]$, 28[nT/mV]이다. 구축한 측정시스템을 이용하여 뇌방전에 의해 발생한 전계와 자계 파형을 관측하고, 파형의 여러 가지 파라미터에 대해 통계적으로 분석하였다. 그 결과 전계와 자계 파형은 극성의존성이 미약하였으며, 전계와 자계 파형의 상승시간과 영점교차시간의 평균값은 각각 $5.5[{\mu}s],\;21[{\mu}s]$로 나타났다.

• Journal of KIEE
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• 제11권1호
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• pp.32-40
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• 2001

This paper presents the detailed statistics on radiation field signatures associated with multiple-intracloud lightning discharges. A transient signal recording system was used to measure the electric and magnetic fields produced by lightning flashes. The measurements were made in th summers of 1995 through 1999, and the location of the observation station was in Inchon on the coast of the Yellow Sea in Korea(37$^{\circ}$25'N, 126$^{\circ}$ 39'E). Most of lightning flashes typically contains between two and five strokes. The individual intracloud stork radiation fields were the bipolar pulse. On the average, the ratio of the peak of the second stroke to the first stroke peak was 75.1$\pm$40.1% for the negative, and a fraction of the subsequent stroke peaks were higher than the first stroke peak. The greater the number of the subsequent stroke order, less time separations between strokes were produced. The mean of the depth of the dip was 81.2$\pm$27.9% for the positive polarity and 75.9$\pm$24.4% for the negative. The depth of the dip increased for the positive bipolar pulses and decreased for the negative as the number of the stroke order increased.

• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.524-529
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• 2013

Recently, researchers have become interested in natural ester fluids, as they are an environmentally friendly alternative to mineral oils. Natural ester fluids are a natural resource made from plants; they have higher biodegradability, flash, and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester fluids also have a higher pour point, viscosity, and water content. These characteristics can hamper circulation and impair the electrical properties of an oil-filled transformer. A large amount of data has been accumulated over the years in regards to mineral insulating oil involving dielectric breakdown voltage and lightning impulse tests. However, natural ester fluids have not had their electrical properties sufficiently characterized. In this paper, we present an investigation into the characteristics of the electrical discharge development in natural ester fluids and in an oil-filled transformer near the pour points. The experiment results show that the electrical properties decreased according to a decrease in the ambient temperature and freezing time. It was found that the pour point and water content of natural ester fluids have a significant effect on the electrical properties.

• 조명전기설비학회논문지
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• 제28권5호
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• pp.68-75
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• 2014

Cascaded applications of surge protective devices(SPDs) are required in order to reduce the stress on the electrical and electronics equipment being protected, and the energy coordination between the cascaded SPDs is very important. This paper deals with the experimental results obtained from the installation conditions of full-scale SPDs. The energy coordination between the upstream Class I SPD and the downstream Class II SPD was measured using a $10/350{\mu}s$ impulse current due to direct lightning flashes. The distances between the cascaded SPDs were 3, 10, and 50m, and the maximum test current was 12.5kA. As a result, the energy sharing between cascaded SPDs was dependent on the voltage protection level of each SPD and the distance between two SPDs. An overview of how to select SPD ratings in applications of cascaded SPDs system was discussed based on the energy coordination between the two SPDs. The proposed test results for the energy coordination between two-stage cascaded SPDs can be used in effective applications of SPDs.

• 비파괴검사학회지
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• 제37권2호
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• pp.91-98
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• 2017

Recently, composite materials have been mainly used in the main wings, ailerons, and fuselages of aircraft and rotor blades of helicopters. Composite materials used in rapid moving structures are subject to impact by hail, lightning, and bird strike. Such an impact can destroy fiber tissues in the composite materials as well as deform the composite materials, resulting in various problems such as weakened rigidity of the composite structure and penetration of water into tiny cracks. In this study, experiments were conducted using a 2 kW halogen lamp which is most frequently used as a light source, a 2 kW near-infrared lamp, which is used for heating to a high temperature, and a 6 kW xenon flash lamp which emits a large amount of energy for a moment. CFRP composite sandwich panels using Nomex honeycomb core were used as the specimens. Experiments were carried out under impact damages of 1, 4 and 8 J. It was found that the detection of defects was fast when the xenon flash lamp was used. The detection of damaged regions was excellent when the halogen lamp was used. Furthermore, the near-infrared lamp is an effective technology for showing the surface of a test object.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1917-1919
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• 1996

This paper aims to extract the air clearance in 22.9KV the metal enclosed switchgear. First, we investigated the actual conditions on the clearance in the metal enclosed switchgear which has been used in domestic. The test model and 9 test electrodes for the air insulation strength tests have been designed and manufactured based on the investigation results. To find optimal clearance in the metal enclosed switchgear, we performed 50% flash-over test by the up and down method and lightning impulse withstand voltage test. And we obtained results that the clearance or phase-to-phase is 230 [mm] and clearance or phase-to-earth is 210[mm].

• 대기
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• 제26권2호
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• pp.321-336
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• 2016

Damages caused by torrential rain occur every year in Korea and summer time convection can cause strong thunderstorms to develop which bring dangerous weather such as torrential rain, gusts, and flash flooding. On 6 August 2013 a sudden torrential rain concentrated over the inland of Southern Korean Peninsula occurred. This was an event characterized as a mesoscale multicellular convection. The purpose of this study is to analyze the conditions of the multicellular convection and the synoptic and mesoscale nature of the system development. To this end, dynamical and thermodynamic analyses of surface and upper-level weather charts, satellite images, soundings, reanalysis data and WRF model simulations are performed. At the beginning stage there was a cool, dry air intrusion in the upper-level of the Korean Peninsula, and a warm humid air flow from the southwest in the lower-level creating atmospheric instability. This produced a single cell cumulonimbus cloud in the vicinity of Baengnyeongdo, and due to baroclinic instability, shear and cyclonic vorticity the cloud further developed into a multicellular convection. The cloud system moved southeast towards Seoul metropolitan area accompanied by lightning, heavy precipitation and strong wind gusts. In addition, atmospheric instability due to daytime insolation caused new convective cells to develop in the upstream part of the Sobaek Mountain which merged with existing multicellular convection creating a larger system. This case was unusual because the system was affected little by the upper-level jet stream which is typical in Korea. The development and propagation of the multicellular convection showed strong mesoscale characteristics and was not governed by large synoptic-scale dynamics. In particular, the system moved southeast crossing the Peninsula diagonally from northwest to southeast and did not follow the upper-level westerly pattern. The analysis result shows that the movement of the system can be determined by the vertical wind shear.