• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.150-158
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• 1999

The process of designing protective circuits against damage by transient overvoltages requires much work and expensive equipment. However computer simulation using PSpice can overcome these problems. In this paper a gas tube and a ZnO varistor Pspice-model considering the steepness of the wave-front were presented. The effects of various waveforms on the transient behaviors and firing volt-ages of a gas tube were modeled by controlled voltage source E controlled current source G and TABLE function of PSpice. And the nonlinear characteristics of a ZnO varistor were modeled by controlled voltage source E and H. To estimate the characteristics of the models proposed various waveforms specified in IEC Std. 1000310-4-5 were used in the simulation and the actual tests. The simulation results were compared with test results and showed good agreement.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.10
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• pp.876-882
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• 2002

The microstructure and electrical characteristics of ZPCD (ZnO-$Pr_{6}O_{11}$-CoO-$Dy_2O_3$) -based varistor ceramics were investigated with various $Pr_{6}O_{11}$/CoO ratios and sintering temperatures. The density of varistor ceramics with $Pr_{6}O_{11}$=1.0 was almost constant with sintering temperature, whereas it was increased noticeably in $Pr_{6}O_{11}$=0.5. Increasing $Pr_{6}O_{11}$ content enhanced the densification for any CoO content and the density was greatly affected not by CoO content but by $Pr_{6}O_{11}$ content. The varistor ceramics with $Pr_{6}O_{11}$/CoO=0.5/l.0 exhibited a higher nonlinearity than any other composition ratios. In particular, the varistor ceramics sintered at $1350^{\circ}C$ exhibited the best electrical properties, with nonlinear exponent of 37.8, leakage current of 7.6 ${\mu}$A, and tan $\delta$ of 0.059.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.876-881
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• 2011

The sintering, defect and grain boundary characteristics of Bi-based ZnO chip varistor (1,608 mm size) have been investigated to know the possibility of lowering a manufacturing price by using 100 % Ag inner-electrode. The samples were prepared by general multilayer chip varistor process and characterized by shrinkage, SEM, current-voltage (I-V), admittance spectroscopy (AS), impedance and modulus spectroscopy (IS & MS) measurement. There are no problems to make a chip varistor with 100% Ag inner-electrode in the sintering temperature range of 850~900$^{\circ}C$ for 1 h in air. A good varistor characteristics ($V_n$= 9.3~15.4 V, a= 23~24, $I_L$= 1.0~1.6 ${\mu}A$) were revealed but formed $Zn_i^{{\cdot}{\cdot}}$(0.209 eV) as dominant defect, and increased the distributional inhomogeneity and the temperature instability in grain boundary barriers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.203-204
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• 2006

Nano-Varistors fabricated with ZnO 30nm and 80nm powders were studied about the electrical characteristics with AC accelerated degradation in this paper Especially, ZnO nano-powder varistors were sintered m air at $1050^{\circ}C$ and analyzed the phenomenons of before and after AC degradation test. The stress conditions of AC degradation test were $1.0V_{1mA}$ $115{\pm}2^{\circ}C$ for 24h. 80nm-varistor was exhibited better performance than 30nm-varistor m the electrical stabilities. And then 80nm-varistor resulted m the degradation characteristics that the variation rate of operating voltage, nonlinear coefficient and leakage current was -0 3%, -0 4% and -3 3%, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.489-494
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• 2001

In this thesis, the microstructure and electrical properties of ZnO varistors were investigated according to ZnO varistors with various formulation. A∼E's ZnO varistor ceramics were exhibited good density, 95% of theory density and low porosity, 5%, wholly. The average grain size of A-E's ZnO varistor ceramics exhibited 11.89$\mu\textrm{m}$, 13.57$\mu\textrm{m}$, 15.44$\mu\textrm{m}$, 11.92$\mu\textrm{m}$, 12.47$\mu\textrm{m}$, respectively. Grain size of C's ZnO varistor is larger and grain size of A and D's are smaller than other varistors. In the microstructure, A∼E's ZnO varistor ceramics sintered at l130$^{\circ}C$ was consisted of ZnO grain(ZnO), spinel phase(Zn$\sub$2.33/Sb$\sub$0.67/O$_4$), Bi-rich Phase(Bi$_2$O$_3$) and inergranular phase, wholly. Reference voltage of A∼E's ZnO varistor sintered at 1130$^{\circ}C$ decreased in order D, E > A > B > C's ZnO varistors. Nonlinear exponent of varistors exhibited high characteristics, above 30, wholly. Consequently, C's ZnO varistor exhibited good nonlinear exponent, 68. Lightning impulse residual voltage of A, B, C and E's ZnO varistors suited standard characteristics, below 12kV at current of 5kA.