• Title/Summary/Keyword: impulse currents

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Effects of the Injected Number and Amplitude of 8/20 [μs] Impulse Current on the Life of ZnO Varistors (8/20 [μs] 임펄스전류의 인가횟수와 크기가 ZnO바리스터의 수명에 미치는 영향)

  • Lee, Bok-Hee;Li, Feng
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.21 no.1
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    • pp.118-124
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    • 2007
  • This paper presents the effects of the injected number and amplitude of impulse current on the service life of ZnO varistors for low voltages. To analyze the effects of lightning impulse currents on the performance of ZnO varistors, the measurements of resistive leakage current and power dissipation at the power frequency ac voltage before and after the injections of the $8/20[{\mu}s]$ impulse currents were made. As a consequence, the duration and amplitude of resistive leakage current flowing through ZnO varistor were increased with increasing the number of injections of the $8/20[{\mu}s]$ impulse currents. It is desirable that the service life of ZnO varistors should be evaluated as a function of the number and amplitude of lightning impulse current.

Effective impulse impedances of a deep-driven ground rod combined with other grounding electrodes (다른 형상의 접지전극에 접속된 심매설 접지전극의 실효임펄스임피던스)

  • Lee, Bok-Hee;Chang, Keun-Chul;Lee, Su-Bong
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2004.05a
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    • pp.565-569
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    • 2004
  • This paper deals with the characteristics of potential rise and effective impulse impedance of deep-driven ground rods that are used in high resistivity soil or in confined places such as downtown. Also the effects of the impulse and fault currents on the deep-driven ground rods combined with different type grounding electrodes like as mesh grids and counterpoises are described. The $8/20{\mu}s$ impulse current and other wave currents with different rise times are injected into the test ground rod and the effective impedances are examined. The most effective way to obtain the fine transient impedance behaviors of deep-driven ground rods is to reduce the inductive component of grounding electrode systems combined with other ground electrodes.

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A Fundamental Study on the Impulse Responses of Ground Rod Attendant upon Soil Discharges (토중방전을 수반하는 접지봉의 임펄스응답에 대한 기초적 연구)

  • Yoo, Yang-Woo;Cho, Sung-Chul;Lee, Bok-Hee
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.28 no.4
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    • pp.62-69
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    • 2014
  • This paper deals with the fundamental characteristics of transient and conventional ground impedances associated with soil discharges when the lightning impulse voltage was applied to a small-sized ground rod. The potential rise responses of the test ground rod to impulse currents were observed. The current-voltage (I-V)curves, transient and conventional ground impedance curves were examined.. To analyze the transient behaviors of ground rod attendant upon soil discharges, the impulse responses of ground rod were compared with those of non-inductive resistor. As a consequence, the potential rise and impedance of ground rod were reduced and the currents dispersed into the earth were increased due to soil discharges near the ground rod. Soil discharges are classified into two regimes; ionization and breakdown phenomena. The potential rise and impulse impedance of ground rod are significantly decreased by breakdown processes in soil.

Transient Impedance of the Ground Grid and Deeply-driven Ground Rod (그리드접지와 심매설 접지전극의 과도임피던스)

  • Lee, Bok-Hee;Lee, Su-Bong;Lee, Tae-Hyung;Jung, Hyun-Uk;Jeong, Dong-Cheol;Gil, Hyoung-Jun
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2005.05a
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    • pp.240-243
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    • 2005
  • This paper presents the transient behaviors of grounding system impedance against lighting impulse currents. The dynamic characteristics of the deeply driven ground rod and grounding grid subjected to the impulse current with various rise time were investigated. It was found that 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 ground impedance of grounding system in the short time domain.

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Fracture and Protection Technologies against Impulse of Power Arresters (전력용 피뢰기의 임펄스에 의한 파손과 대척 기술)

  • 한세원;조한구;김석수
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.07a
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    • pp.190-193
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    • 2001
  • ZnO varistors have been widely used to protect power system and electronic system against overvoltages based on their excellent nonlinearity. In order to increase their protection capability, the fracture and protection technologies of arresters have to study according to their applications, namely ImA DC voltage, leakage currents, impulse residual voltages, withstanding capability to impulse surge, and energy absorption capability. ZnO varistors which have nonlinear current-voltage characteristic name a number of failure mechanism when ZnO elements absorb surge energies. Failure mode by thermal stress and Pin hole are among the most common failure mechanism at the high current surge current. In this study, the fracture mechaism of power arresters are introduced and protection technologies are researched. In particular the effect of thermal stress by surge currents to ZnO elements and methods against arc surge energy through withstand structure design of arrester are discussed.

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Transient impedance characteristics according to the injection position of deep-driven ground rods (심매설 접지전극의 전류인가위치에 따른 과도접지임피던스 특성)

  • Lee, Bok-Hee;Li, Feng;Lee, Su-Bong;Lee, Song-Zhu;Jeon, Byung-Wook;Eom, Ju-Hong;Cho, Sung-Chul;Lee, Tae-Hyung
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2008.05a
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    • pp.297-300
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    • 2008
  • This paper presents the behaviors of transient and conventional grounding impedances of a deep-driven ground rods associated with the injection point of lightning impulse currents. The transient impedance of deep-driven ground rods under lightning impulse currents were higher than the static ground resistance. The transient grounding impedances strongly depend on the injection point and size of grounding electrodes and the rising time of impulse current. Reduction of ground system inductance is an important factor to lightning surge protection.

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Analysis of soil discharge characteristics in sand with water content (수분 함유량에 따른 모래의 지중방전 특성 분석)

  • Lee, Bok-Hee;kim, Hoe-Gu;Park, Geon-Hun;Lee, Kyu-Sun;Ahn, Chang-Hwan
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2008.05a
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    • pp.436-439
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    • 2008
  • It has been known that the value of soil resistance drops when a high impulse curennt is injected into a grounding electrode. In this paper, impulse generator is used to investigate the dry soil and wet soil characteristics in cylinderical test cell. The impulse resistances and breakdown characteristics were discussed based on its voltage and current traces. As a result, sand resistances are decreased with increasing the applied currents. It was thought that a decrease in resistance of dry sand with increasing current is due to both thermal and ionization processes. On the other hand, in case there is no water presence in the soil, the reduction in resistance as the currents are of dry sand increased is mainly due to the ionization process.

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Transient Ground Impedances According to Shapes of Grounding Electrodes (접지전극의 형상에 따른 과도접지임피던스)

  • Lee, Bok-Hee;Lee, Su-Bong;Lee, Tae-Hyung;Jung, Hyun-Uk;Jeong, Dong-Cheol
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.20 no.1
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    • pp.65-70
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    • 2006
  • This paper presents the transient behaviors of grounding system impedance against lightning impulse currents. The dynamic characteristics of the deeply driven ground rod and grounding grid subjected to the impulse current were investigated. 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 ground impedance of grounding system Also, the deeply-driven ground rod was effective to reduce the transient ground impedance in time domain of miceroseconds.

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.

Grounding Impedance Behaviors Associated with the Current Injection Point and the Length of Counterpoise (매설지선의 길이와 전류인가점에 따른 접지임피던스특성)

  • Li, Feng;Lee, Bok-Hee
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.23 no.6
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    • pp.66-71
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    • 2009
  • This paper presents the grounding impedance behaviors of counterpoise exposed to impulse currents. The transient and conventional grounding impedances of three counterpoises having the length of 10, 30 and 50[m] were measured and analyzed as a function of the injection point of impulse currents. As a result, the trend of the conventional grounding impedances measured as a function of injection of impulse current is similar to the transient grounding impedance of counterpoise. The injection point of impulse current has great influence on the transient grounding impedance characteristics of counterpoise. The transient grounding impedance characteristics in a short time range are strongly dependent on the length of counterpoise. The transient characteristics of grounding impedance of 10[m] counterpoise subjected to the impulse current was capacitive behavior, on the other hand, those of 30[m] and 50[m] counterpoises were inductive behavior. It is found that the grounding conductor should be connected to the central point of counterpoise.