• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.2
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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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.4
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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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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• v.13 no.5
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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%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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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%.

• Proceedings of the KIEE Conference
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• 2009.07a
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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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• v.4C no.5
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.546-547
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• 2005

This study aims to evaluate the properties and the performance of the newly designed disconnector for surge arrester. This disconnector was verified with the performance in long-duration current impulse test and high current impulse test. And time-current characteristic test was done at 20A, 200A and 800A(3points) for simulating the internal fault condition of the arrester. The results of this test was very good. Consequently, the newly designed disconnector was, evaluated that it is possible to be used for surge arrester in distribution line system.

• 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.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.1
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• pp.94-100
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• 2005

This paper presents the behaviors of transient and effective impulse impedances of a long ground rod associated with the current injection points. The laboratory test for the time domain performance of actual-sized model ground rod subjected to a lightning stroke current has been carried out The transient ground impedances of long ground rods under impulse currents were higher than the ground resistance. Both of the ground resistance and the effective impulse ground impedance decrease with increasing the length of the ground rods. Also, the effective impulse ground impedances are significantly increased in fast rise time ranges. The reduction of the ground resistance is decisive to improve the impulse impedance characteristics of grounding systems. When the test current is injected at the bottom of ground rod, the oscillating pulses with high frequency are included on the wave front of ground rod potential and the effective impulse impedances are higher than any other cases.