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Epoxy resin as a typical electrical insulation material has been widely applied in the power equipment. However, the electrical properties of epoxy resin are strongly affected by the surface charge accumulation. One way to solve the surface charge accumulation may be to use the nonlinear resistive field grading nanocomposites. In this paper, we aim to study the effect of ZnO nanoparticles on the surface...
ZnO-based varistors have been widely applied in surge protection devices because of their excellent nonlinear current-voltage (I-V) characteristic and energy absorption ability. Manganese is always added into ZnO-based varistors in order to enhance the nonlinear characteristic of materials. In the present work, the dielectric properties of Mn-doped ZnO-Bi2O3 varistors at extremely low temperatures...
The interior distributions of electrical and dielectric properties of ZnO varistor at initial aging stage are investigated. Two commercial varistors at different aging stages were compared. These two varistors were cut into slices along the axial direction, and then the variations of varistor slices' electrical and dielectric performances were obtained. The results show that the interior performance...
ZnO varistors have been extensively used against transient surges because of the excellent nonlinearity. ZnO varistors are obtained by sintering semiconducting ZnO powder with small amount of metal oxide additives. Amongst, Mn-doping is effective in the enhancement of the nonlinearity. In this paper, the relationship between the microstructure, the electrical and dielectric properties of Mn-doping...
ZnO-based varistors have been extensively used for the protection of devices and equipment against voltage surges because of their exceptional nonlinearity in current-voltage characteristics and the ability to absorb large amounts of energy. Since the composition and fabrication process are complicated, impurities are inevitable in the varistors. Sodium impurities are frequently present in the raw...
Considering the response of free charges to high frequency alternating current (AC) electric field and multiemission and capture processes of weakly bound charges, dielectric relaxation effect of free carriers are proposed in this paper. According to this model, free charges and bound charges are regarded as the same except for the difference in transport distance, which is defined by the frequency...
ZnO varistors are used extensively as the surge suppressor in the form of surge arresters in the power protection against lightning, temporary over-voltages, switching surges, transients, etc. In this research, DC degradation process at 50 mA/cm2 for 115 hours and restorability by heat-treatment at 800 oC for 24 hours for ZnO varistors were performed. The breakdown field E1mA (electric field at 1...
The electrical and dielectric properties of a commercial ZnO-based varistor ceramics were measured in the process of 8/20mus impulse current degradation with a current density of 1725A/cm2. The characteristic of U-I in the pre-breakdown region was mainly investigated. It was found that the varistor voltage U1mA will first increase rapidly with the times of impulse, and then remain stable and finally...
Recently, universal power law becomes widely used. In this paper, it was used to study the ZnO/Bi2O3 ceramics. Bi2O3 is the only additive of ZnO here in order to directly study the effect of Bi2O3 in ZnO. ZnO samples with different content of Bi2O3 were made by the traditional ceramic technique. Then the microstructure of the acid erosion surface was observed by polarized optical microscope, the dielectric...
In this paper, ZnO varistor+Al2O3 ceramic+ZnO varistor insulators were made, in which the conductivity and permittivity of ZnO varistors were controlled by changing its voltage gradient. Then the influences of conductivity and permittivity of ZnO varistors on the DC and pulsed surface flashover voltage in vacuum were experimentally investigated. The experimental results indicated that the DC and pulsed...
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