Papers by Keyword: Varistor

Abstract: A varistor equivalent electrical network generally used in CAD software is presented. Based on a PSPICE model already presented [5] a PSIM model valid in static regime was developed. Since correct parameter estimation is very important for a model valid in transient regimes, a more detailed varistor electrostatic capacity C_p determination for future model improvements is presented.

Abstract: In this paper, the influences of MnO2 and V2O5 on the varistor properties of ZnO- V2O5-based ceramics were examined. The results show that, the addition of MnO2 to the ZnO-V2O5-based ceramics was found to improve varistor properties. The sintered temperature was benefit to enhancing the growth of crystals of the samples and the non-ohomic coefficient can be improved. The samples have non-ohmic coefficient α=27.8 and varistor voltage U1mA=60.9V/mm when they are sintered at 1100°C with 2 hours.

Abstract: Nanometer-sized ZnO powder was synthesized at low decomposing temperature by polyacrylamide-gel method where Acrylamide was used as monomer, and N,N-methylene-bisacrylamide as lattice reagent. The characteristic of powders were studied by X-ray diffraction and scanning electron microscope (SEM). The results indicated uniform distribution of nanoZnO particles. Also electrical properties were investigated at different sintering temperatures of 800, 900 and 1000 ° C. It was observed that increase in sintering temperature, resulted in increase in the grain size of the varistor ceramics. The observed nonlinearity in current – voltage characteristic was explained by the existence of potential barrier at the grain boundaries and lowering of the barriers.

Abstract: ZnO is a semiconductor with direct band gap that because of its optical and electronically properties has very interesting for researchers. Wide application of this compound in electronic and optic like piezoelectric transducer, gas sensor, optical waveguide, thin conductor layer and transparent, varistors, photocells, optical U.V. equipments and also variety medical applications with concerning its nature friendly cause that to find the economical method for mass production be concerned. During recent decay, many methods such as sol-gel, wet chemistry, CVD & MOCVD, hydrothermal methods and development process have been invented for ZnO production. The most common problems of these methods are complexity of production process, need to expensive equipments, need to expensive raw materials, need to exceedingly pressure and temperature etc. In this research with activation of Zn as the raw material, nanoparticles of ZnO has been product by a planetary mill and hydride action that this method has ability to extensile in industrial range.SEM investigations approve the nanosize of produced particles. Morphology of particles is more similar to hexagonal crystal structure. Process efficiency is 100 percent and x-ray diffraction (XRD) of resultant powder verifies this. After synthesis and characterization of ZnO nanopowder as one of its application, varistor was made and then electrical property of this part was evaluated.

Abstract: In this work, systematic substitution of ZnO with SnO₂ in ZnO-based varistor composition was investigated through analysis of densification, phase formation, microstructure and non-linear properties. The general formula was Zn_0.96-xSn_xBi_0.02Co_0.02O_β with x = 0, 0.01, 0.02 and 0.04. The high rate of densification starting at 800°C is believed to be related to Bi₂O₃ via liquid-phase sintering. The complex nature of this multi-phasic varistor system was demonstrated through occurrence of different phases at different sintering temperatures. The low-temperature pyrochlore (Bi₂Sn₂O₇) started to dissociate at approximately 1100°C with the spinel (Zn₂SnO₄) forming afterwards. The grain size variation with composition might be induced by the changes in the availability of Bi₂O₃ which has been reported to help facilitate abnormal grain growth. All samples sintered at 1200°C, with data extrapolation, possessed breakdown voltages of higher than 1400 V/cm.

Abstract: The influence of TiO₂ nano powder on the electrical properties and microstructure of TiO₂ ceramics was studied. The results showed that nano additive reduces the size of TiO₂ grain. The results also showed that the breakdown voltage and nonlinear constant of the samples were improved and the dielectric constant was reduced by doping nano-titania. An optimal composition dopant with 6 mol% nano-titania exhibited a low breakdown voltage of 11.3 V/mm, a nonlinear coefficient of 5.5, an ultrahigh relative dielectric constant of 7.11×10⁴ and relatively low loss of 0.28.

Abstract: Bi₂O₃ is an important additive in the composition of ZnO varistors. However, the effect of Bi₂O₃ on novel SnO₂ based varistors is still unclear. This paper reports the nonlinear electrical characteristics of (98.95-x)mol%SnO₂-0.5mol%CoO-0.05mol%Nb₂O₅- xmol% Bi₂O₃ (x = 0, 0.05, 0.1, 0.5 mol%) system, and the influence of sintering temperature is also investigated. The addition of Bi₂O₃ can improve the electrical nonlinearity of SnO₂-CoO-Ta₂O₅ based varistors, this may be due to the higher barrier height and barrier voltage. The optimum Bi₂O₃ doping level is between 0.1-0.5mol% and the optimum sintering temperature is 1350°C.

Abstract: The voltage and electric field distribution in an arrester are very important for its long operation 15 kV with and without pollution. In order to clarify the influence of pollution severity conditions on metal oxide surge arrester, the finite element method (FEM) compilation of the voltage distribution in the ZnO column varistors under different pollution layer conductivity (200 μS, 70μS, 20μS) and clean was employed using the FEMLAB package.

Abstract: The nonlinear electrical behavior and dielectric properties of WO3-based ceramics with various La2O3 contents have been investigated. Breakdown voltages Eb of WO3 doped with La2O3 are lower than that of undoped WO3, indicating that the dopant can reduce the breakdown voltage. The dielectric constant of doped samples is higher than that of undoped samples, and the high dielectric constant makes them suitable as capacitor-varistor materials. The theory defects in the crystal lattice was introduced to explain the nonlinear electricial behavior of the La2O3-doped WO3 ceramics. In view of these electrical characteristics, the WO3 ceramic doped with La2O3 is a viable candidate for capacitor-varistor functional devices.

Abstract: TiO₂ varistors doped with 0.1 mol% Ta and different concentrations of Pr³⁺ were obtained by ceramic sintering processing at 1400 °C and their properties were characterized by XRD, SEM, I-V and impedance spectroscopy. The effect of Pr on the microstructure, nonlinear electrical behavior and dielectric properties of the Ta-doped TiO₂ ceramics were investigated. It is found that Pr affects the grain size, electrical properties and the dielectric properties of the TiO₂-based varistors. The samples have the nonlinear coefficients (α) values of (3.0-5.0) with low breakdown voltages (4-30 V/mm). A small quantities of Pr can improve the nonlinear properties of the samples significantly. It was found that an optimal doping composition of 0.5 mol% Pr³⁺ leads to a low breakdown voltage of 9.2 V/mm, a high nonlinear constant of 4.9 and an ultrahigh electrical permittivity of 8.38×10⁴ (at 1 kHz), which is consistent with the highest grain boundary barriers of the ceramics. In view of these electrical characteristics, the TiO₂-0.5 mol% Pr³⁺ ceramic is a viable candidate for capacitor-varistor functional devices. The defects theory was introduced to explain the nonlinear electrical behavior of Pr-doped TiO₂ ceramics.