• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.338-341
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• 2006

This paper presents the leakage current characteristics of ZnO varistors exposed to the $8/20{\mu}s$ lightning impulse currents as functions of the number of injection and amplitude of impulse currents. The surge simulator system ECAT that can generate $8/20{\mu}s$ impulse currents with a peak short-circuit of $5[kA_p]$ was used. Leakage currents flowing through ZnO varistors subjected to the $8/20{\mu}s$ impulse currents were measured under 60 Hz AC voltages. The trend curves of resistive leakage current of ZnO varistors were analytically calculated.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.199-205
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• 1993

Effects of grain size distribution on the breakdown voltage of ZnO varistors were investigated in the ZnO-Bi2O3-CoO-Sb2O3 and ZnO-Bi2O3-CoO-Sb2O3-Cr2O3 systems, respectively. The grain size was increased with increasing sintering temperature maintaining lognormal distribution in both systems. The width of grain size distribution of ZnO-Bi2O3-CoO-Sb2O3 system was narrower than that of ZnO-Bi2O3-CoO-Sb2O3 system. The breakdown voltage(Vb) was decreased by increasing sintering temperature(1000~135$0^{\circ}C$) and sintering time(0.5~5hr), due to the enhancement of ZnO grain growth. The current path of the ZnO varistor was dependent on the distribution of the largest grains (chains of long grains) between the electrodes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.242-245
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• 2000

The electrical properties of ZPCCE (ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Er$_2$O$_3$) based varistors were investigated with sintering temperature in range of 1335 to 135$0^{\circ}C$ for 1h. As the sintering temperature increases, the nonlinear exponent decreased, but was high beyond 40 except for 1.0 mol% Er$_2$O$_3$. Among all ZPCCE varistors, the varistor having the highest nonlinear exponent was obtained by sintering at 1335$^{\circ}C$, containing 2.0 mol% Er$_2$O$_3$ and then the nonlinear exponent was 78.05, and the varistors with 0.5 mol% Er$_2$O$_3$ exhibited the lowest leakage current of 1.92 $\mu$A.A.A.

• Journal of the Korean Ceramic Society
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• v.29 no.2
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• pp.161-165
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• 1992

Nonlinear exponents and electron trap density variations were observered in ZnO-Bi2O3-MnO2 ternary ZnO varistors as a function of heat treatment temperature. Three kinds of ZnO varistor compositions were selected; i.e. 99.0 ZnO-0.5 Bi2O3-0.5 MnO2, 98.5 ZnO-1.0 Bi2O3-0.5 MnO2, and 98.0 ZnO-1.5 Bi2O3-0.5 MnO2 in mol%. Sintering was done at 1150$^{\circ}C$ for three hours, and heat treatments were done at 500$^{\circ}C$, 700$^{\circ}C$, and 900$^{\circ}C$. When heat treated at 500$^{\circ}C$, nonlinear exponents were increased regardless of the Bi2O3 amount. Increasing heat treatment temperature above 500$^{\circ}C$ resulted in lowering nonlinear exponents. Nonlinear exponents seem to be related to the 0.17 and 0.33 eV electron traps which are possibly of intrinsic origin.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1631-1633
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• 2004

The surge current characteristics of ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3-Dy_2O_3$-based varistors were investigated with various $Dy_2O_3$ contents. The sintered density decreased in the range of $5.2{\sim}4.6g/cm^3$ with increasing $Dy_2O_3$ content. The incorporation of $Dy_2O_3$ markedly enhanced the nonlinear properties of varistors above 10 times in nonlinear exponent, compared with the varistor without $Dy_2O_3$. The varistor ceramics doped with 0.5 mol% $Dy_2O_3$ exhibited the highest electrical stability. However, the remainder varistors resulted in thermal runaway due to low density of varistor ceramics. The clamping voltage ratio exhibited a minimum value of 2.03 in 1.0 mol% $Dy_2O_3$ at surge current of 100 A(8/20 ${\mu}s$).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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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.

• Journal of the Korean Ceramic Society
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• v.43 no.6 s.289
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• pp.383-388
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• 2006

The varistor properties and DC accelerated aging characteristics of $ZnO-Pr_{6}O_{11}-CoO-Cr_{2}O_{3}$-based varistors were investigated at different $La_{2}O_3$ contents in the range of $0{\sim}2.0mol%$. The varistors doped with 0.5 mol% $La_{2}O_3$ exhibited good nonlinearity, with 81.6 in nonlinear coefficient. Increasing the $La_{2}O_3$ content further to 2.0 mol% caused the sintered density to increase, and the breakdown voltage and nonlinearity to decrease abruptly. The varistors with 0.5 mol% $La_{2}O_3$ exhibited the high electrical stability, with -1.14% in variation rate of breakdown voltage, -3.7% in variation rate of nonlinear coefficient, and +100% in variation rate of leakage current for specified DC accelerated aging stress condition (95% of breakdown voltage/$150^{\circ}C$/24 h).

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1673-1675
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• 2000

The nonlinearity and degradation characteristics of $Pr_{6}O_{11}$-based ZnO varistors doped with, $Er_{2}O_3$ were investigated. The varistors were sintered at 1335$^{\circ}C$ in the addition range of 0.0 to 2.0 mol% $Er_{2}O_3$, respectively The varistor doped with $Er_{2}O_3$ exhibited more higher nonlinearity than that without $Er_{2}O_3$. Most of the varistors containing 0.5 mol% $Er_{2}O_3$ showed nonlinear exponent more than 70 and a excellent stability, which the variation rate of the varistor voltage and the nonlinear exponent is -0.85% and -1.43%. respectively, even under 3rd d.c stress, such as (0.80 $V_{1mA}/90^{\circ}C$/12h)+(0.85$V_{1mA}/115^{\circ}C$/12h)+(0.90$V_{1mA}/120^{\circ}C$/12h). Consequently, since $Pr_{6}O_{11}$-based 2nO varistors doped with 0.5 mol% $Er_{2}O_3$ have an excellent stability as well as good nonlinearity, it is expected to be usefully used to develop the advanced varistors in future.

• Transactions on Electrical and Electronic Materials
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• v.6 no.4
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• pp.144-148
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• 2005

The microstructure and electrical properties of varistor ceramics, which are composed of Zn-Pr­Co-Cr-Dy-oxide system, were investigated at various dysprosia $(Dy_2O_3)$ addition contents. The $DY_2O_3$ microstructurally played the role of inhibition for the densification and grain growth. As the $DY_2O_3$ content increased, the density decreased in the range of $5.51-4.90 g/cm^3$, reaching maximum at $0.5 mol\%$ and the average ZnO grain size decreased in the range of $17.7-6.0{\mu}m$. The incorporation of $DY_2O_3$ significantly improved the nonlinear properties of varistors, above 30 in nonlinear exponent, compared with that without $DY_2O_3$. The varistors with the best performance of nonlinear properties was obtained $DY_2O_3$ content of $1.0 mol\%$, 49 in nonlinear exponent and $0.5{\mu}A$ in leakage current.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.359-362
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• 1988

In this papers, in order to decreased the ZnO varistor breakdown voltage, additives the $TiO_2$ with ZnO varistors. The effects of addition $TiO_2$ with ZnO varistor are discussed. Observation of ZnO varistor microstructures are photospectroscopy and SEM, and variation of phase are XRD analysis. Experimental results, the more increased the $TiO_2$ contents the more decreased the mean grain size of ZnO. Also, results of XRD analysis, the more increased the $TiO_2$ contents the more increased the spinel structures.