• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1531-1532
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• 2006

Recently, the natural environment changes drastically, and the frequency of occurrence for lightning has gradually been increased. Such lightning delivers high volume of energy along the power line and communication line to the equipment in use. The high volume of energy arising from the lightning surge develops in fast velocity to destroy the facilities in power source and many other facilities in operation in sequential destruction with vast energy. In this thesis, the analysis on the change of clamping voltage characteristics by the contact resistance and lead inductance by using several case studies through the application of element for preventing the short circuit of Metal Oxide Varistor for ZnO.

• 전기의세계
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• 제31권6호
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• pp.445-449
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• 1982

This Paper describes the influence of additive concentrations and sintering temperature on the surge protection performance in ZnO ceramic varistors. It is found from the experiments that the metal-oxide semiconductors based oi ZnO with an additive incorporation of 0.50% molx(Bi$\_$2/O$\_$3/+MnO+CoO+Cr$\_$2/O$\_$3/+2Sb$\_$2/O$\_$3/) and sintered at 1250.deg. C present excellent V-I characteristics in view of transient surge suppression. Gapless arrester element with aluminum electrodes shows also good reliability against impulse shock and marks a low voltage clamping ratio(V$\_$1KA/V$\_$1mA/<2.0) compared with the conventional SiC varistors.

• 조명전기설비학회논문지
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• 제29권4호
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• pp.116-125
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• 2015

This paper presents experimental results obtained from actual installation conditions of surge protective devices (SPDs), with the aim of understanding the coordination of cascaded Class I and Class II SPDs. This paper also proposes effective methods for selecting and installing coordinating cascaded SPDs. The residual voltage of each SPD and the energy sharing of an upstream Class I tested SPD and a downstream Class II tested SPD were measured using a $10/350{\mu}s$ current wave. In coordinating a cascaded voltage-limiting SPD system, it was found that energy coordination can be achieved as long as the downstream SPD is a metal oxide varistor with a higher maximum continuous operating voltage than the upstream SPD; however, it is not the optimal condition for the voltage protection level. If the varistor voltage of the downstream SPD is equal to or lower than that of the upstream SPD, the precise voltage protection level is obtained. However, this may cause serious problems with regard to energy sharing. The coordination for energy sharing and voltage protection level is fairly achieved when the cascaded SPD system consists of two voltage-limiting SPDs separated by 3 m and with the same varistor voltage.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.358-362
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• 1995

Precision electronic equipments are composed of sophisticated microcircuits that are extremely vulnerable to lightning-caused voltage spike. This transient voltage spike may cause upset, latent failure or interference on electronic equipments. In order to develop efficient lightning protection measures on AC power lines for a road traffic controller, experimental surge immunity tests were conducted according to IEC standard 801-5. The combination of gas tube arrester and metal-oxide varistor was installed at the input of AC power lines and the silicon avalanche suppressor installed at the output of DC power supply as lightning protection measures.

• 한국안전학회지
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• 제30권4호
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• pp.39-45
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• 2015

This paper deals with development of integrity evaluation instrument for the power line surge protective device. A reliable power supply is an essential element in the developed information and communication society by highly advances in IT technology. However, the lightning incidence also increased with the recent extreme weather events. In Korea, in order to protect the electrical system from lightning surge, SPD(Surge Protective Device) has been used for these past 30 years. However, the method of diagnosing the safety of the SPD in the industry is insufficient. In this paper, SPD integrity evaluation system was composed of a variable DC power source unit, voltage-current sensor and the embedded controller. In order to measure V-I characteristics of MOV, 3 type samples were degraded by impulse current generator. After impulse tests, the varistor voltage of all samples and nonlinearity coefficient were decreased. It confirmed the utility of the developed equipment by this experimental test and the reliability of SPD is expected for surge accident prevention when applied to industrial plant.

• 한국세라믹학회지
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• 제41권8호
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• pp.605-609
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• 2004

다양한 금속산화물(NiO, MgO, Cr$_2$O$_3$) 첨가에 따른 ZnO 바리스터의 미세구조, 전기적, 유전적 특성을 조사하였다. 평균 결정립 크기는 NiO 첨가로 증가한 반면 Cr$_2$O$_3$ 첨가로 감소하였다 이로 인해 바리스터 전압은Cr$_2$O$_3$ 첨가시 더 높게 나타났다. 바리스터 가운데서 Cr$_2$O$_3$가 첨가된 바리스터가 비직선 지수가 40.5, 누설전류가 2.7 $\mu$A로 가장 우수한 비직선성을 나타내었으며, 유전손실도 0.0589로 비교적 낮게 나타났다.

• 한국전기전자재료학회논문지
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• 제17권9호
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• pp.924-929
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• 2004

The microstructure, electrical and dielectric characteristics of $ZnO-{Pr}_6{O}_11-{CoO}-{Dy}_2{O}_3$-based varistors were investigated without and with various metal oxide additives(NiO, MgO, Cr$_2$O$_3$). The average grain size decreased in the range of 18.4 $\backsim$ 11.5 $\mu$m, in order of NiO\longrightarrowMgO\longrightarrow{Cr}_2{O}_3$ and the density decreased in the range of 5.62 \backsim 5.33 $g/{cm}^3$ in order of NiO\longrightarrowCr$_2$O$_3$\longrightarrowMgO. While, the nonlinear exponent increased In the range of 19.8$\backsim$67.4 in order of NiO\longrightarrowMgO\longrightarrow${Cr}_2{O}_3$ and the leakage current decreased in the range of 25.6 $\backsim$ 1.2 $\mu$A in order of NiO\longrightarrow${Cr}_2{O}_3$\longrightarrowMgO. Among all varistors, the Cr$_2$O$_3$-added varistor exhibited the highest nonlinearity, with a nonlinear exponent of 67.4 and a leakage current of 1.2 $\mu$A. Furthermore, this varistor exhibited the lowest dielectric dissipation factor of 0.0407.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1529-1531
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• 1999

The main functions of AC railroad vehicles arresters is to protect the main transformer from lightening impulse or switching impulse surge, then the MOV(metal oxide varistor) elements rated of 10kA is applied. The residual voltage and surge energy absorption are important parameters in designing arrester, these must be carefully decided with considering protecting level of impulse environment of system. The purpose of this study is to discuss the residual voltages and the energy absorption capability by impulse currents on MOV elements for railroad vehicles, and to introduce design factors which act as optimal protecting condition against impulse currents.

• 조명전기설비학회논문지
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• 제25권2호
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• pp.120-125
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• 2011

SPDs are increasingly being used against lightning and switching surge according to the applicable revised standard and equipotential grounding system. SPDs are equipped usually with a MOV voltage regulating element. The MOV, however, always is exposed to the danger of thermal runaway resulting from inrushing temporary overvoltage and deterioration. In this paper, the authors made two prototype SPDs built-in Instantaneous trip device and analyzed their limiting voltage through test of the MOV breakdown. As the result of the analysis, the SPDs built-in Instantaneous trip device was proven to be effective for protecting MOV against thermal runaway and Instantaneous trip device react for limiting voltage is considered that is applicable to SPD.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.2065_2066
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• 2009

In this paper, we have developed high performance SPD(surge protective device) and evaluated the characteristics in comparison with typical SPD used in the inside and outside of the country. The new SPD was composed of MOV(metal oxide varistor), GDT(gas discharge tube) and impedance such as resistors, capacitors or varistors. To estimate operating the characteristic of the SPD which was developed, it was measured surge voltage caused by fault current or surge according to IEC 61000-4-5. As a result it was found that the power supply was cut off by high performance SPD when caused a short-circuit. In addition we could know that it could prevent ELB(earth leakage breaker)'s malfunction caused by surge.