• 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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• 2005.05b
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• pp.46-49
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• 2005

This paper presents the electrical characteristics of metal oxide varistors for lightning surge arresters. ZnO varistors were fabricated with typical ceramic production methods and two types of varistors were also prepared to be compared. The nominal discharge current and line discharge class of those varistors are $10kA(8/20{\mu}s)$ and class 3, respectively. The diameter of varistors manufactured and prepared were in the range of 61.6~65.0mm and the thickness of those were in the range of 27~42.52mm. The reference and residual voltage were tested and reference and residual voltage per 1mm and the ratio of reference and residual voltage were calculated. The reference voltage per 1mm of varistors manufactured was about 175V/mm but that of A's and B's varistors was nearly 200V/mm. The residual voltage exhibited the same trends as the reference voltage, so the reference and residual voltage per 1mm of domestic varistors should be increased. According to the results of tests, it is thought that if the reference and residual voltage per 1mm were increased to 200V/mm and 330V/mm, domestic ZnO varistors would be possible to apply to the station class arresters in the near future.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.747-750
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• 2003

The microstructure and nonlinear properties of ZPCMR-based varistors were investigated with various additives. The density of varistors were gradually decreased for the same R in order of NiO, MgO, and $Cr_2O_3$, respectively. The ZPCR-based varistors were not affected by NiO and MgO additives in nonlinear properties, whereas greatly affected by $Cr_2O_3$. Among the ZPCCR-based varistors, ZPCCD varistor exhibited the highest nonlinear properties, in which the nonlinear exponent is in the range of $40.5{\sim}67.4$ and the leakage current is in the range of $1.2{\sim}2.7{\mu}A$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.834-839
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• 2000

The structural properties that SEM photograph of ZnO varistors surface studied by fractal mathematics program were investigated to verify the relations of electrical characteristics. The SEM photograph of ZnO varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of ZnO varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in ZnO varistors surface was decreased by increasing of Sb$_2$O$_3$ addition. The spinel structure was formed by Sb$_2$O$_3$addition and it was depressed the ZnO grain formation. The grain size of ZnO by Sb$_2$O$_3$addition were from 5 to 10[${\mu}{\textrm}{m}$]. Among of ZnO varistors, fractal dimension of ZnO4 was very high as a 1.764. The density of grain boundary in ZnO2 and ZnO3 varistors surface was 15[%] by formed spinal structure. The breakdown electric field of ZnO2 that fractal dimension has 1.752 was very high to be 8.5[kV/cm]. When the fractal dimensin was high, the grain shape of ZnO varistors was complex and the serial layers of ZnO grain was increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.551-554
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• 2000

The stability of $Pr_6$$O_{11}$-based ZnO varistors doped with $Y_2$$O_3$ was investigated under various d.c. stresses. The varistors were sintered at $1350^{\circ}C$ for 1h in the addition range of 0.0 to 4.0 mol% $Y_2$$O_3$. The varistors doped with $Y_2$$O_3$ exhibited much higher nonlinearity than that without $Y_2$$O_3$. In Particular, the varistors containing 0.5 mol% $Y_2$$O_3$ showed very excellent V-I characteristics, which the nonlinear exponent was 51.19 and the leakage current was 1.32 $\mu\textrm{A}$. And these varistors also showed an excellent stability, which the variation rate of the varistor voltage and the nonlinear exponent were -0.80% and -2.17%, respectively, under 4th 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)+(0.95 $V_{1mA}$/$125^{\circ}C$/12h). Consequently, since $Pr_ 6$$O_{11}$-based ZnO varistors doped with 0.5 mol% $Y_2$$O_3$ have an excellent stability as well as good nonlinearity, it is expected to be usefully used to develop the superior varistors in future.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1647-1653
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• 2011

In the case of an urban rail chopper type subway train, varistors have been installed for protecting usual electronic equipments, semiconductor devices(diodes, transistors, thyrister, etc.) communications, measuring, control device and absorbing opening & closing surge of electromagnetic valve. These varistors were steadily reduced dielectric strength as becoming superannuated. Thus there is a problem that reacts more sensitive at the same surge in the general control operation. On existing maintenance, there is not specific standard to replace superannuated varistor. So when maintaining chopper type subway train, all varistors or old varistors that workers checked a discoloration & crack with the naked eye and noticed degradation smell by deterioration are replaced. This study suggests detail standards for judgement that varistors are good or bad chopper type subway train, and it draw a efficient maintenance which efficient maintenance can check more easy the degradation properties variation.

• Transactions on Electrical and Electronic Materials
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• v.10 no.4
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• pp.125-130
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• 2009

The clamping voltage characteristics and accelerated aging behavior of CoCrTb-doped Zn/Pr-based varistors were investigated for different sintering temperatures. The best clamping voltage characteristics were obtained for the varistors sintered at $1330^{\circ}C$, with a clamping voltage ratio (K) of 1.63 at a surge current of 5 A and 1.75 at a surge current of 10 A. The varistors sintered at $1330^{\circ}C$ exhibited the highest stability, with -0.1% in $%{\Delta}E_{1\;mA}$, -0.2% in $%{\Delta}{\alpha}$, and +15.5% in $%{\Delta}J_L$ for E-J characteristics under a stress state of 0.90 $E_{1\;mA/120^{\circ}C$ /24 h. Furthermore, it exhibited $%{\Delta}{\varepsilon}_{APP}$' of -0.7% and $%{\Delta}tan{\delta}$ of +5.7% for dielectric characteristics under the same stress state.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05a
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• pp.47-51
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• 2001

The structural properties of varistors surface studied by fractal phenomenon were investigated to verify the relations of electrical characteristics. The SEM photograph of varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in varistors surface was decreased by increasing of oxide antimony addition. The grain size of devices by oxide antimony addition were from 5 to $10[{\mu}m]$. The fractal dimension and electrical properties of varistors surface was related to between grain boundary and grain density. The grain size was decreased by increasing of fractal dimensions.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.581-584
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• 2000

This paper describes the effect of lightning impulse current on ZnO varistors(390 V, 6.5 kA) used in low-voltage AC mains as a protective device against transient overvoltages. A lightning impulse current standardized in IEC 61000-4-5 is applied to the varistors, and the energy applied to the varistor at each time is about 12 J. In the experiment, various Parameters such as leakage current, reference voltage are measured with the number of applied impulse current. Also, micro-structure changes of the varistors after applying the lightning impulse current of 200 times are compared. The electrical characteristics of the varistors are degraded by overtime impulse current, showing increase in leakage current and decrease in reference voltage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.315-316
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• 2005

This paper describes the AC accelerated ageing characteristics of zinc oxide varistors for the station class lightning surge arresters. ZnO varistors whose rated voltage were 3.27kV, 4.00kV, and 6.00kV were manufactured with general ceramic production methods. The power loss of sample A varistors rapidly increased and eventually showing the thermal run-away, but sample B and sample C varistors exhibited negative creep phenomena in power losses during the test.