• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2005년도 추계학술대회 논문집 전기물성,응용부문
• /
• pp.100-102
• /
• 2005

This paper presents evaluation of the electrical uniformity of zinc oxide varistors for lightning arresters. Two types of varistors were prepared which are a domestic varistor destroyed in the long duration current impulse withstand test and a new imported varistor. The domestic varistor exhibited good electrical uniformity except destroyed parts, but the imported varistor showed the worse results.

• 한국결정성장학회지
• /
• 제17권2호
• /
• pp.63-68
• /
• 2007

EMI filter와 같은 적층형 세라믹 제조 시 공정 상 많은 문제점이 야기된다. 특히 표면과 계면에서의 crack, camber, delamination 같은 결함이 없는 적층체를 얻기 위해 서로 다른 두 재료의 동시 소성에 의한 수축율 조절이 필수적이다. 본 연구에서는 ferrite의 분체 특성을 통해 varistor/ferrite의 동시소성 거동을 연구하였다. ferrite 분말을 각각 24시간, 48시간, 72시간 분쇄하여 varistor와 ferrite 각각의 슬러리를 제조하고 doctor blade법으로 green sheet를 제조하였다. 슬러리는 분말 55wt(%)에 binder solution 45wt(%)로 혼합하여 제조하였다. Varistor와 ferrite green sheet는 $80 kg/cm^2$로 적층하여 $900^{\circ}C$, $1000^{\circ}C$에서 3시간 소결 하였다. 그 결과 분쇄시간과 소결온도 조절로 결함이 없는 동시 소성된 ferrite/varistor 적층체를 제조 할 수 있었다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 D
• /
• pp.1692-1695
• /
• 1999

The nonohmic characteristics of ZnO-$Pr_6O_{11}$-CoO-based ceramic varistor doped with $Dy_2O_3$ in the range $0.0\sim2.0mol%$ sintered at $1300^{\circ}C$ and $1350^{\circ}C$ were investigated. 98.5 ZnO-$0.5Pr_6O_{11}$-1.0CoO varistor sintered at $130^{\circ}C$ exhibited higher nonlinear coefficient of 36 than the established Pr-based varistor. The four-component-system varistor such as 96.5 ZnO-$0.5Pr_6O_{11}$-1.0CoO-$2.0Dy_2O_3$ exhibited very highly nonohmic characteristics, which has nonlinear coefficient of 53.9. 98.5ZnO-$0.5Pr_6O_{11}$-1.0CoO varistor sintered at $1350^{\circ}C$, in contrast with that of $1300^{\circ}C$, exhibited approximately ohmic characteristics but nonlinear coefficient of varistor doped with 0.5mol% $Dy_2O_3$ showed higher nonlinear coefficient of probably 35. Consequently, it can be confirmed that $Dy_2O_3$ acted as additive of improvement on nonlinear coefficient. It is estimated that $Dy_2O_3$ will be used as additive of improvement on nonlinear coefficient to develop a goof ZnO varistor.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
• /
• pp.552-556
• /
• 2002

The microstructure and electrical characteristics of A~C's ZnO varistors fabricated according to variable sintering condition, which sintering temperature is $1130^{\circ}C$ and speeds of pusher are A: 2mm/min, B: 4mm/min, C: 6mm/min, respectively, were investigated. In the microstructure, A~C's ZnO varist-ors fabricated variable sintering condition was consisted of ZnO grain(ZnO), spinel phase$(Zn_{2.33}Sb_{0.67}O_4)$ Bi-rich $phase(Bi_{2}O_{3})$, wholly. Varistor voltage of A~C's ZnO varistors sintered at $1130^{\circ}C$ increased in order A < B < C's ZnO varistors. C's ZnO varistor exhibited good characteristics that nonlinear exponent is 31.70. Leakage current of A~C's ZnO varistors exhibited below 2mA at rated voltage. Lightning impulse residual voltage of A's ZnO varistor suited standard characteristics, which is 3.85kV at 2.5kA, 4.4kV at 5kA and 5.16kV at 10kA. After multi lightning impulse residual voltage test of A's ZnO varistor exhibited good discharge characteristics which ZnO varistor reveals no evidence of puncture, flashover, cracking in visual examination. After high current impulse test of A's ZnO varistor exhibited good discharge characteristics, which variation rate of residual voltage is 0.4% before and after test, and revealed no evidence.

• 한국전기전자재료학회논문지
• /
• 제19권7호
• /
• pp.662-666
• /
• 2006

Microstructure and electrical properties of ZnO varistors as a function of sintering temperature and times were investigated. Sintering temperature and times greatly affected electrical properties and Bi-rich liquid phase of the microstructure. The varistor which were sintered at $1125^{\circ}C\sim1150^{\circ}C$, for 2 hr exhibited the varistor voltage$(V_c)$, nonlinear coefficient $(V_{10mA}/V_{1mA})$, leakage current$(I_L)$ dielectric constant and dissipation factor as $225\sim250V/mm,\;0.89\sim0.92,\;0.8\sim1.1{\mu}A,\;720\sim740\;and\;1.8\sim2.0%$, respectively.

• 한국세라믹학회지
• /
• 제25권5호
• /
• pp.552-560
• /
• 1988

ZnO low voltage varistor was obtained by varying a) the amount of seed grains, b) the size of seed grains, and c) sintering temperature. Also, the optimum condition for fabricating the ZnO seed grains was studied. Large ZnO seed grains were obtained by washing a ZnO sintered body containing 1m/of BaCO3 in boiling water. When the seed grains were added, abnormal grain growth occurred, and the varistor voltage sharply decreased. However, when more than 5w/o of seed grain content was added, the varistor voltage gradually increased. When 10w/o seed grains of 75~106${\mu}{\textrm}{m}$ were added and sintered for 2 hours at 1200 to 125$0^{\circ}C$, low voltage varistor properties with V1mA/mm of 19V/mm and nonlinear exponent ($\alpha$) of 12 occurred.

• Transactions on Electrical and Electronic Materials
• /
• 제15권6호
• /
• pp.348-352
• /
• 2014

In light of the sure protection function, the most important factors of a varistor are the clamping voltage ratio and degradation characteristics. The degradation characteristics of Pr/Co/Cr/Er co-doped zinc oxide varistors were investigated by impulse currents (0.4~2.1 kA) stress for the specified content of $Er_2O_3$ (0.5 and 2.0 mol%). The varistor doped with 2.0 mol% $Er_2O_3$ exhibited the best clamp characteristics, with the clamp voltage ratio (K) in the range of K = 1.63~1.88 at the impulse currents of 5-50 A. However, the varistor doped with 0.5 mol% exhibited excellent electrical stability, with variation rates for the breakdown field, for the nonlinear coefficient, and for the leakage current density of -6.9%, -12.6%, and -14.3%, respectively, after application of an impulse current of 2.1 kA. In contrast, the varistor doped with 2.0 mol% was destroyed after application of an impulse current of 1.2 kA.

• 한국신뢰성학회지:신뢰성응용연구
• /
• 제5권2호
• /
• pp.221-239
• /
• 2005

General chip SMD parts(chip resistance, chip capacitor, chip varistor etc.) are very wide used electronics parts for IT units. But, failure modes are indistinct for these chip parts. In factory and field the failure modes are recognized to accidental failure mode caused by potential defect. In this paper used chip varistor ALT(Accelerate Life Test) test for verify general failure modes in chip SMD parts. Also the results are useful for general chip SMD ALT tests.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
• /
• pp.821-823
• /
• 1988

The electrical properties of ZnO varistors fabricated by the second firing method were investigated. The nonlinear coefficient of ZnO varistor fabricated by this method is similar to that of commercial ZnO varistor. But the breakdown voltage is higher than that of commercial ZnO varistor. These results are attributed to grain boundary diffusion of $Bi_{2}O_{3}$ by second firing.

• 한국신뢰성학회:학술대회논문집
• /
• 한국신뢰성학회 2005년도 학술발표대회 논문집
• /
• pp.51-67
• /
• 2005

General chip SMD parts(chip resistance, chip capacitor, chip varistor etc.) are very wide sed electronics parts for IT units. But, failure modes are indistinct for these chip parts. In factory and field the failure modes are recognized to accidental failure mope caused by potential defect. In this paper used chip varistor ALT(Accelerate Life Test) test for verify general failure modes in chip SMD parts. Also the results are useful for general chip SMD ALT tests.