• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.1
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• pp.71-77
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• 2010

Protection against lightning surge is an essential part of almost any electrical and electronic equipment today. Metal Oxide Varistor(MOV) is the single most important component in the overwhelming majority of the Surge Protective Devices(SPD) designated to provide such protection. In this paperr various types of MOV based SPD are inspected and experiments are carried out on the side effects of the low Measured Limiting Voltage(MLV) characteristics. Experiment results show that a lower MLV could cause a higher Temporary Overvoltage(TOV)-induced SPD failure rate in the field, and SPD are more likely to be victims rather than protectors in a TOV scenario. This means that from a safety perspective, the SPD should be specified with higher TOV withstand capability(UT) and faster SPD disconnector.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.6
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• pp.75-81
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• 2013

In this paper, protection coordination between residual current devices and surge protective devices in low-voltage consumer's distribution systems are presented. In the case that a surge protrctive device(SPD) is located on the load side of an residual current device(RCD), when the surge is injected from the source side of the RCD, most of injected surge currents are split into the RCD and the protection coordination between the SPD and RCD is improper, three of 6 specimens experience unintended operation due to test impulse currents. Also when the surges is injected from the load side, a lot of the surge currents is split into the SPD, but a half of test specimens causes nuisance trip. Coordination between SPD and RCD is not valid. When installing SPD, it is important to select SPD after due consideration of the protection voltage level of metal oxide varistor embedded in RCD. It is expected that the results obtained from this work could be useful to improve the protection effects of SPD in low-voltage distribution systems.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.250-253
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• 2007

Gas Discharge Tubes (GDTs) are widely used as surge protectors for commnuication applications due to their small internal capacitance. In these days, however, they are mostly used in combined configurations, because the activation voltage required to initiate the discharge process in the GDTs for sufficient amount of time can be large enough to damage surge-sensitive protected circuits. For GDTs with a considerably high initial over-voltage value, we should limit the peak voltage using a TVS or filter. As for ZnO varistors, even though their performance for voltage restriction is excellent, their applications in high-frequency commnuication circuits have been limited because of higher internal capacitance when compared to the GDTs. In order to develop a surge protector for commnuication applications by taking advantages of these two devices, we built a combination circuit that connects a GDT and a ZnO varistor along with a choke coil in common and differential modes. We describe how the applied SPDs operate in protection process steps with the actual data obtained from the residual voltage measurements at each step. The experiment results show that the surge voltage restriction with the choke coil is more effective in 100 [kHz] RingWave voltage than in lightning impulse voltage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.419-422
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• 2001

The electrical properties of Pr$_{6}$O$_{11}$-based ZnO varistors composed of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Dy$_2$O$_3$- based ceramics were investigated with CoO content in the range of 0.5~5.0 mol%. As CoO content is increased, the average grain size and the density were increased in the range of 9.86~27.22 $\mu$m and in the range of 5.25-5.55 g/cm$^3$, respectively. The varistor voltage was decreased in the range of 235.32~86.01 V/mm due to the increase of average grain size with CoO content. The varistors doped with CoO in the rage of 1.0~2.0 mol% exhibited a high nonlinearity, in which is above 55 in the nonlinear exponent and below 1.5 $\mu$A in the leakage current. Increasing CoO content further greatly decreased the nonlinearity.ity.ity.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.12
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• pp.1085-1091
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• 2006

The microstructure, electrical properties, and its stability of (Pr, Co, Cr, La)-doped ZnO varistors were investigated at different sintering temperatures in the range of $1230{\sim}1300^{\circ}C$. As the sintering temperature increased, the sintered density increased from 5.50 to $5.77g/cm^3$, the varistor voltage decreased from 777.9 to 108.0 V/mm, the nonlinear coefficient decreased from 77.0 to 7.1, and the leakage current increased from $0.4{\mu}A\;to\;50.6{\mu}A$. On the other hand, the donor concentration increased from $0.90{\times}10^{18}\;to\;2.59{\times}10^{18}/cm^3$ and the barrier height decreased from 1.89 to 0.69 eV with increasing temperature. The stability of nonlinear electrical properties was obtained from sintering temperature of $1260^{\circ}C$. The varistors sintered at $1260^{\circ}C$ marked the high electrical stability, with $%{\Delta}V_{1mA}=+1.9%,\;%{\Delta}a=10.6%,\;and\;%{\Delta}I_L=+20%$ for DC accelerated aging stress state of $0.95V_{1mA}/150^{\circ}C/24h$.

• Electrical & Electronic Materials
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• v.6 no.1
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• pp.69-79
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• 1993

ZnO 바리스터는 전기전자 장치에 비이상적인 써어지 혹은 잡음신호가 침입하는 것을 막기위해서 폭넓게 사용되고 잇다. 많은 연구자들은 저전압 바리스터를 제조하기 위해서 요러가지 방법을 제시하였다. 그렇지만 그러한 방법들은 6V이하의 동작 전압을 갖는 바리스터를 제조하기는 어렵다. 본 연구에서는 새로운 3-성분 종입자법으로 제조한 바리스터의 전도특성을 보고하고자 한다. 온도범위 20-150.deg.C 및 전류 범위 $10^{-8}$~$10^{-1}$A/$cm^{2}$에서 관찰된 바리스터의 전도특성은 측정전류가 증가함에 따라서 다른 기구를 갖는 3개의 영역으로 구분되었다. 측정전류가 $10^{-3}$ A/$cm^{2}$이하인 경우에 오옴전도 혹은 누설전류 영역으로 해석 할 수 있었다. 측정 전류가 $10^{-3}$ A/$cm^{2}$ 부근에서는 이중 쇼트키 장벽에 의한 전도로 해석할 수 있었으며 또한 $10^{-3}$ A/$cm^{2}$ 이상의 전류 영역에서는 턴넬 전도 전류로 해석 할 수 있었다. 이상의 결과로 부터 3-성분 종입자법으로 저전압 바리스터를 제조하는 방법은 지금까지 보고된 어느 다른 방법보다도 우수하며 그 전도기구를 제시하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1117-1123
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• 2005

In this study, our varistors based on M. Matsuoka's composition were fabricated with ZnO nano-powder whose sizes were 50 nm and 100 nm. Before fabrication of ZnO nano-powder varistors, structure and Phase were analyzed by FE-SEM and XRD with size of ZnO nano-powders to obtain manufacturing information to fabricate the first ZnO varistors using by nano-powders. As a results of these analyses, calcination and sintering temperatures were respectively designed at $600^{\circ}C\;and\;1050^{\circ}C$. ZnO nano-powder varistors were analyzed by SEM and XRD to measure the changes of microstructures and phase after sintered by out process conditions. Also, electrical properties of ZnO nano-powder varistors were obtained by capacitance-voltage, frequency-teal impedance, and current-voltage corves. Our ZnO nano-powder varistors had about 2.5 times of electric field at varistor voltage as compared with normal ZnO varistors fabricated with micro-powder. Also, leakage current and non-liner coefficient respectively had $2.0{\times}10^{-6}A/cm^{-2}$ and 41 for ZnO nano-powder varistors with 50 nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1125-1128
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• 2004

This paper presents the temperature characteristics with structure of 18 kV lightning arresters for distribution. Three types of polymer arresters were fabricated and ceramic type arrester was also ready to investigate. Below $100^{\circ}C$, three types of polymer arresters exhibited almost the same leakage current value, but above $100^{\circ}C$, polymer arrester that arrester module was injected into polymer housing with grease exhibited the highest leakage current and the arrester with the lowest leakage current was the arrester that silicon rubber was directly injected to arrester module. The rising of leakage current of polymer arrester with grease was because of existing grease between FRP winding and silicon housing, and reducing the insulation characteristics of the grease. All polymer arresters exhibited the same temperature characteristics but ceramic typr arrester was slower than polymer arrester in heat emission despite lowest leakage current. It was thought that the air layer between ZnO varistor blocks and ceramic housing prevented the heat emission. However, in spite of the difference of the structure, the variation of the surface temperature of all arresters exhibited the same result.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1142-1145
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• 2004

ZnO surge arresters continuously endure the operating voltages during the operation course, and in the mean time, which need to withstand occasionally transient voltages of lightning and switching overvoltages. Under these voltages, the ZnO varistors inside arresters would have aging phenomena, one important result of aging phenomena is the increasing of resistive currents of varistors, which leads to the increasing of power losses of varistors. And the operating voltage is continuously applied on the ZnO varistors, there is a degradation phenomenon existing in ZnO varistors. When the degradation reaches a certain degree, then the arrester must stop operation. The degradation is related to the applied voltage ratio, the applied voltage ratio is high, the degradation is quickly. When the power loss is higher than the thermal dispersion ability of house of arrester, then the arrester will thermally breakdown. In this study the thermal stability characteristics of surge arresters for high power wil be discussed on the view point of watt losses and thermal breakdown.