• 한국전기전자재료학회논문지
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• 제15권2호
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• pp.190-197
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• 2002

In this thesis, ZnO varistors with various formulation, such as A∼E, were fabricated according to ceramic fabrication method. The microstructure, electrical properties, and surge characteristics of ZnO varistors were investigated according to ZnO varistors with various formulation. In the microstructure, A∼E\`s ZnO varistor ceramics sintered at 1130$\^{C}$ was consisted of ZnO grain(ZnO), spinel phase (Zn$\_$2.33/Sb$\_$0.67/O$\_$4/), Bi-rich phase(Bi$_2$O$_3$) and intergranuler phase, wholly. Lightning impulse residual voltage of A, B, C and E\`s ZnO varistors suited standard characteristics, below 12kV at current of 5kA. On the contrary, D\`s ZnO varistor exhibited high residual voltage as high reference voltage. In the accelerated aging test, leakage current and watt loss of B, C and D\`s ZnO varistors increases abruptly with stress time under the first a.c. stress(115$\^{C}$/3.213kV/300h). Consequently, C varistor exhibited a thermal run away. On the contrary, leakage current and watt loss of A and C\`s ZnO varistors which show low initial leakage current exhibited constant characteristics. After high current impulse test, A\`s ZnO varistor has broken the side of varistor but impulse current flowed. On the contrary, E\`s ZnO Varistor exhibited good discharge characteristics which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After long duration impulse current test, E\`s ZnO varistor exhibited good discharge characteristics which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After high current impulse test and long duration impulse current test, E\`s ZnO varistor exhibited very good characteristics which variation rate of residual voltage is 1.4% before and after test.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1418_1419
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• 2009

This paper presents the transient impedance when high current impulse up to 5 kA is applied to a scaled grounding grid in test field. For a realistic analysis of transient impedance on the high current impulse in the ground systems, grounding electrode installed outdoors and impulse current generator was used. The results were discussed based on its voltage and current trace, impulse impedance and V-I curve.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권5호
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• pp.207-214
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• 2004

This paper presents the characteristics of transient and effective impulse impedances for deeply driven grounding electrodes used in soil with high resistivity or in downtown areas. The laboratory test associated with the time domain performance of grounding piles subjected to a lightning stroke current has been carried out using an actual-sized model grounding system. The ground impedances of the deeply driven ground rods and grounding pile under impulse currents showed inductive characteristics, and the effective impulse ground impedance owing to the inductive component is higher than the power frequency ground impedance. Both power frequency ground impedance and effective impulse ground impedance decrease upon increasing the length of the model grounding electrodes. Furthermore, the effective impulse ground impedances of the deeply driven grounding electrodes are significantly amplified in impulse currents with a rapid rise time. The reduction of the power frequency ground impedance is decisive to improve the impulse impedance characteristics of grounding systems.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.212-216
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• 2000

ZnO varistors for distribution surge arrester (18kV, 5kA) were developed and tested microstructure and electrical characteristics. Microstructure of ZnO varistor was consisted of ZnO grain, spinel phase and Bi-rich phase. Average grain size of ZnO varistor was $\mu\textrm{m}$ Reference voltage and lightning impulse residual voltage of ZnO varistor exhibited a good haracteristics above 5.5kV and below 11.56kV, respectively. Consequently, discharge capacity which is the most important characteristics of ZnO varistor for surge arrester exhibited excellent properties above 70kA at twice high-current impulse test. Moreover, variation rate of reference voltage and lightning impulse residual voltage showed below 5% and 2% after high-current impulse test, respectively. Leakage current and watt loss of ZnO varistor will not increase during accelerated aging test at stress condition, such as 3.213kV/$115^{\circ}C$/1000h.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.2050-2058
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• 2018

Impulse characteristic of transmission tower grounding grid is needed for lightning protection of transmission line. This paper describes an outdoor experimental test facility established for large-scale grounding grid of transmission tower, made up of four impulse current generators and a circle current return electrode. The amplitude of impulse current is up to 100 kA. The results of the CDEGS simulation and GPR measurement reveal the uniform current distribution in the test arrangement. An impulse test for a square electrode with extended conductors is carried out in condition of three current waveforms with different amplitude. Based on the electrical network model and iterative algorithm method, a calculation model is proposed to simulate the impulse characteristic of large-scale grounding grid considering soil ionization. The curve of impulse resistance against the current amplitude shows the soil ionization both from the simulation and test. Deviation between the simulation and test result is less than 15%.

• 한국전기전자재료학회논문지
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• 제19권4호
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• pp.398-403
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• 2006

This paper describes the evaluation of the long duration current impulse withstand characteristics of ZnO blocks for high voltage surge arresters. Four ZnO varistors were manufactured with the general ceramic production method and the long duration current impulse withstand test, electrical uniformity evaluation test and microstructure observation were performed. All varistors exhibited high density, which was in the range of $5.42{\sim}5.46g/cm^3$. In the electrical properties, the reference voltage of samples was in the range of $5.11{\sim}5.25\;kV$ and the residual voltage was in the range of $8.314{\sim}8.523\;kV$. In the long duration current impulse withstand test, sample No.2 and No.3 failed at the 2nd and 4th shot of series impulse currents, respectively, but the rest survived 18 shots during the test. Before and after this test, the variation ratio of the residual voltage of samples survived was below 0.5 %, which was in the acceptance range of 5 %. According to the results of the test, it is thought that if the soldering method is improved, ZnO varistors would be possible to apply to the high voltage arresters like the station class and transmission line arresters in the near future.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.486-487
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• 2007

This paper describes the evaluation of long duration current impulse withstand characteristics of ZnO blocks for high voltage surge arresters. Four ZnO varistors were manufactured with the general ceramic production method and three abroad varistors were also prepared to be compared. All varistors exhibited high density, which was in the range of $5.42{\sim}5.49g/cm^3$. In the electrical properties, the reference voltage of all samples was in the range of 5.11~5.72kV and the residual voltage was in the range of 8.314~9.305kV. In the long duration current impulse withstand test, sample 2 and 3 failed at the 2nd and 4th shot of series impulse currents, respectively, but the rest survived 18 shots during the test. Before and after this test, the variation ratio of the residual voltage of samples survived were below 1.7%, which were in the acceptance range of 5%.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2009년도 추계학술대회 논문집
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• pp.331-334
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• 2009

This paper presents the characteristics of external inductor for impulse current waveform with 10/350 ${\mu}s$ time parameters. Impulse generator was composed with capacitor having large capacitance and low working voltage for the safe of operator and small discharging sound. Parallel R-L-C circuits with crow-bar gaps and superposition method were proposed to make a high current lightning impulse according to IEC 62305-1. The high energy inductor with several taps for fitting half decay time T2 within the tolerance range and experimental data of inductance according to charging voltages were suggested.

• 한국소음진동공학회논문집
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• 제18권7호
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• pp.783-789
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• 2008

This experimental study describes the noise reduction and the feasibility of short current of a silencer for a high voltage COS(cut out switch) fuse of a transformer. When a high voltage COS fuse becomes a short circuit by the over current, the strong impulse noise over 150 dB(A) is generated. For the purpose of the reduction of impulse noise, in this study, the diffuser type and the reactive type silencers have been designed and tested, respectively. And also the electrical test on the short current is performed. From the experimental results, the well designed reactive type silencer has been shown to have the noise reduction of about 20 dB(A). It has been found that the feasibility of short current for the COS fuse is closely related to the porosity of the silencer.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1849-1851
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• 2003

To obtain a low ground resistance in high resistivity soil, long vertical ground rods are often used. However, if the lightning current or fault current with high frequency flow into the grounding system, the ground impedance is significantly increased because of the inductive behavior. This paper presents how the impulse current works on the long vertical ground electrodes. The different shape of current was impressed between ground rods and auxiliary electrode by using impulse generator and the ground impedance was calculated from the ground potential rise.