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Stability of Metal-Oxide Varistor Characteristics in Exploitation Conditions

100%
Lončar B., Vujisić M., Stanković K., Osmokrović P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 6
1081-1084
EN
Wide-spread use of metal-oxide varistors for non-linearity over-voltage protection results in a variety of possible working conditions. It is therefore essential to have a thorough insight into their reliability in various exploitation environments. The influences of temperature variation, aging and radiation exposure on metal-oxide varistors characteristics were investigated in this paper. Stable and effective over-voltage protection over a wide temperature range is always a desirable property, one which significantly contributes to overall system reliability. Behaviour of metal-oxide varistors in the temperature range from -50°C to 150°C was investigated. Aging caused by exploitation was investigated by applying 1000 consecutive double exponential over-voltage pulses to the varistors. Resistance of metal-oxide varistors to the radiation is of special interest in nuclear, military, and space technology. Radiation effects of californium-252 combined neutron/gamma radiation were examined. Voltage-current characteristics, voltage-resistance characteristics and the value of breakdown voltage were used to characterize metal-oxide varistors operation. Non-linearity coefficient, defined from the voltage-current curve, was also used as a parameter. Results are presented with the accompanying theoretical interpretations of the observed changes in metal-oxide varistors behaviour.
2
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Gas Electronegativity Influence οn Electrical Breakdown Mechanisms

88%
Lončar B., Radosavljević R., Vujisić M., Stanković K., Osmokrović P.
Acta Physica Polonica A
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2011
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vol. 119
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issue 3
364-368
EN
This paper discusses the role of different gas breakdown mechanisms depending on electronegativity of the gas, at low values of pressure and inter-electrode gap. Static (dc) electrical breakdown of electropositive, electronegative and noble gases has been investigated theoretically, experimentally and numerically. In the case when the electron mean free path is comparable with characteristic dimension of the electrode system (inter-electrode distance d), then the breakdown occurs through the Townsend mechanism. In the case when the electron mean free path is much shorter than the characteristic dimension of the electrode system, the breakdown is said to occur through the streamer mechanism. But, between the regions where the breakdown occurs solely by either the Townsend or the streamer mechanism, there is a region where breakdown occurs by the combination of these two mechanisms. The width of this region expressed by the quantity of pd product (product of pressure, p, and inter-electrode distance, d) depends on observed gas tendency to form negative or positive ions (electronegative and noble gases, respectively). The level of the anomalous Paschen effect expression is dependent on whether the observed gas is electronegative or noble. The combined mechanism effects of breakdown and anomalous Paschen effect are quantitatively determined and theoretically explained within this paper.
3
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Electrical Breakdown Mechanisms in Vacuum Diodes

88%
Osmokrović P., Ilić D., Stanković K., Vujisić M., Lončar B.
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issue 4
585-588
EN
This paper investigates the roles of different mechanisms constituting the process of electrical breakdown in vacuum. Random variable "vacuum breakdown voltage" was measured for pulse breakdowns in five types of vacuum diodes, with different values of vacuum pressure and inter-electrode gap. Conclusions about the influence of vacuum pressure and inter-electrode distance on the parameters of theoretical statistical distributions have been drawn. Based on the distribution to which the "vacuum breakdown voltage" random variable adheres, the dominance of certain breakdown mechanisms has been established for specific ranges of vacuum pressure. The observed absence of anode vacuum breakdown at small inter-electrode gaps has been given a theoretical interpretation.
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