• Title/Summary/Keyword: Lightning Impulse Voltage

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Characteristics of Impulse Discharges in Wet Soil (습한 토양의 임펄스방전특성)

  • Kim, Hoe-Gu;Lee, Bok-Hee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.66 no.2
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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.

An Analysis Method for the Transient Ground Impedance Using Variable Frequency Current and Lightning Impulse (가변주파수 및 임펄스 전류를 이용한 과도접지임피턴스 분석)

  • Cho, Sung-Chul;Eom, Ju-Hong;Lee, Tae-Hyung
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2007.11a
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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.

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Lightning Surge Response Characteristics of Non-tripping Type Earth Leakage Breakers for Impulse (충격파 부동작형 누전차단기의 뇌써지 응답 특성)

  • Lee, J.B.;Myung, S.H.;Cho, Y.G.;Chang, S.H.;Kim, J.S.;Kil, G.S.
    • Proceedings of the KIEE Conference
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    • 2002.07c
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    • pp.1688-1690
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    • 2002
  • The unpredictable threat of lightning surge is ever increasing in today's low-voltage power supplies. Thus Surge protection devices for AC mains are more widely used. The false-tripping of the earth leakage breaker (ELB) can be caused by the installation of surge protection devices with MOV. In order to examine the cause of malfunction, the malfunction characteristics of ELBs applied by lightning surge were investigated experimentally. As a result, all of them brought about malfunctions under 7 kV of the impulse voltage. The suitable position of MOV and use of zener diode were suggested to eliminate the problems.

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Experimental study on the lightning impulse breakdown characteristics of air for the development of air-insulated high voltage apparatuses (고전압 전력기기 개발을 위한 기중 임펄스절연파괴특성에 관한 연구)

  • Kang, Hyoun-Gku;Kim, Joon-Yeon;Seok, Bok-Yeol;Kim, Dong-Hae
    • Proceedings of the KIEE Conference
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    • 2009.07a
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    • pp.1473_1474
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    • 2009
  • To develop electrically reliable high voltage apparatuses, the experimental study on the electrical breakdown field strength is needed, as well as theoretical approach. In this paper, lightning impulse breakdown characteristics considering utilization factors are investigated for the establishment of insulation design criteria of an high voltage apparatus. The utilization factors are represented as the ratio of mean electric field to maximum electric field. Dielectric experiments are performed by using five kinds of sphere-plane electrode systems made of stainless steel. As a result, it is found that dielectric characteristics are affected by not only gap length but also utilization factor of electrode systems. The results are expected to be applicable to the design of high voltage apparatuses.

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Wet Flashover Characteristics and Reform Measure of a Conventional Lightning Rod against Lightning Impulse Voltages (뇌임펄스전압에 대한 돌침형 피뢰침의 주수섬락특성과 개선 방안)

  • 이복희;강석만;엄주홍;이승칠;김승지
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.16 no.3
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    • pp.93-100
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    • 2002
  • In this paper, in ordor to examine the relevant technical facts which are very instructive to revise the domestic standard for lightning protection systems, standards and technical guideline for the protection of structure against lightning were reviewed, and several issues of the domestic standards were experimentally investigated. As a consequence, the insulator of relatively low implse voltage and a large percentage of lighting rods is flashovered by relatively low impulse voltage and a lage percentage of lighting current flows through supporting mast. Thus the potential gradient in the vicinity of supporter for lighting rods is extremely increased and the role of lighting propection systems is nullified. It seems obvious that the flashover of insular supporting lighting rod can range from erratic operation of microelectronic devices to minor physical ham or even death, or costly damage electrical equipment.

Characteristics of lightning impulse breakdowns in inhomogeneous $SF_6$ gas gap (불평등전장에서 $SF_6$ 기체의 뇌임펄스 절연파괴특성)

  • Lee, B.H.;Choi, H.S.;Oh, S.K.;Li, F.
    • Proceedings of the KIEE Conference
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    • 2004.07c
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    • pp.1921-1923
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    • 2004
  • V-p characteristics and the discharge luminous characteristics in inhomogeneous $SF_6$ gas gap under the positive and negative lightning impulse voltages are presented. The test gap was composed of the plane-to-plane with a needle-shaped protrusion. The applied voltage and the predischarge current were measured by the electric field sensor and the shunt of 50 ${\Omega}$, respectively. The light emission signals were observed by a photomultiplier tube, and a high-speed camera. In a consequence, the dielectric strengths of $SF_6$ gas gap under positive lightning impulse voltages were independent of the gas pressure. In the presence of the positive polarity, the branches of discharge channel were created and the directions of the discharge paths were random. On the other hands, the discharge paths of the negative polarity were more thicker and brighter.

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Analysis and Countermeasures for False-Tripping of Earth Leakage Breaker Due to Lightning Surge (누전차단기의 뇌써지 동작특성 분석 및 오동작 대책)

  • Lee, Jae-Bok;Myeong, Seong-Ho;Jo, Yeon-Gyu;Jang, Seok-Hun;Kim, Jeom-Sik
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.51 no.10
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    • pp.479-484
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    • 2002
  • Recently it is reported that many a malfunction of ELB which is represented by non-operated type ELB for an impulse wave, is caused by lightning impulse and transient ground potential rise due to nearby lightning strokes. In order to examine the cause of malfunction, 5 samples were investigated experimentally in this study. As each ELB has a different leakage current detecting circuit and wiring method, various characteristics were measured. As a result, all of them brought about malfunctions under the lightning impulse voltage less than 7 kV and the surge current less than 3 kA. Also the different aspects were measured with a polarity of injected surge and a position of MOV to protect the inner circuit of ELB. The Position and effects of protecting devices were suggested as a remedy.

The Lightning Impulse Properties and Breakdown Voltage of Natural Ester Fluids Near the Pour Point

  • Choi, Sun-Ho;Huh, Chang-Su
    • Journal of Electrical Engineering and Technology
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    • v.8 no.3
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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.

Change of the Microstructure of ZnO Arrester block by Lightning Surge Current and Ageing test (뇌서지전류와 Ageing에 의한 산화아연형 피뢰기 소자의 미세구조변화)

  • Lee, Bok-Hee;Kang, Sung-Man
    • Proceedings of the KIEE Conference
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    • 2000.07c
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    • pp.1877-1879
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    • 2000
  • This paper deals with the change of the micro-structure of ZnO associated with lightning surge current and ageing test. In this work, a surge current generator which can produce 8/20 [${\mu}s$], 6 [kA] impulse current is designed and fabricated to simulate the lightning impulse current. The residual voltage and leakage current flowing to ZnO blocks are observed. Also a compensation circuit was used in resistive current measurement. The micro-structures of ZnO arrester block were significantly changed by lightning surge current and accelerated temperature ageing test.

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Design of Insulation and Bending Test for a 154 kV Class HTS Cable (154 kV급 HTS 케이블의 절연설계 및 굴곡시험)

  • Choi, Jin-Wook;Choi, Jae-Hyeong;Lim, Eung-Choon;Kim, Hae-Jong;Cho, Jeon-Wook;Kim, Sang-Hyun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.21 no.11
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    • pp.1024-1028
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    • 2008
  • It is important that study on cryogenic electrical insulation design to develop the cold dielectric(CD) type HTS cable because the cable is operated under the high voltage environment in cryogenic temperature. This paper proposes two types of insulation design to carry out the maximum insulation design for 154 kV-class HT cable. The proposed insulation design method takes into consideration AC and lightning impulse withstand voltage so as to prevent AC breakdown for power frequency operating voltage during operating the cable and breakdown for lightning impulse voltage. The final insulation thickness is determined by selecting high value out of two insulation thickness calculated through the two insulation design methods. And we researched electrical insulation characteristics of HTS cable according to bending ratio and the number of bending.