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| 2. |
- Serdyuk, Yuriy, 1963
(författare)
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Computer Modelling of Electrophysical Phenomena in High Voltage Insulation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different kinds of dielectrics are used for high voltage insulation. In most of the cases, they are combined into complex insulating systems forming macro- and micro-scale composite structures. Presence of interfaces in a composition leads to specific phenomena when subjected to high electric fields, first of all to the accumulation and polarization of charges on the interfaces and to electrical discharges in the gas phase having the lowest dielectric strength among other materials. This thesis focuses on developing computational approaches for simulations and analysis of these processes. Computer modelling of dielectric relaxation, effective dielectric properties and local characteristics (distributions of electric fields and power losses) of the composites is performed for binary mixtures with regular and stochastic structures using experimentally obtained frequency dependent properties of the constituents as input parameters. The model is verified by comparing the computed results with the experimental data. The developed procedure is then applied to analyze interfacial charges, fields and losses in a water-treed polymeric insulation of a high voltage cable. The computational model of electrical discharges in gases utilizes the drift-diffusive approximation. Simulations are performed for two different arrangements, where the air gap is comprised by metallic electrodes and by electrodes covered with solid dielectric layers. In the first case, conditions of propagation of positive and negative streamers in low background fields are examined. In the second case, the developed procedure is used to study dynamics of discharges in a hybrid air-dielectric insulation and for analysis of processes determining its performance. The results of the simulations are compared with available experimental data. Further, the elaborated computer model is applied to examine a possibility of generating homogeneous plasmas by means of high-frequency discharges in helium under different conditions. Microscopic and integral properties of such plasmas determining their usability in technological applications are analysed.
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| 3. |
- Serdyuk, Yuriy, 1963, et al.
(författare)
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Dielectric Properties of Composite Structures: 3D Simulations versus Experiments
- 2002
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Ingår i: IEEE Annual Report Conference on Electrical Insulation and Dielectric Phenomena. - 0780375025 ; , s. 142-145
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Konferensbidrag (refereegranskat)abstract
- Results of numerical simulations of the dielectric properties of binary composites with three-dimensional structures are verified by means of comparison with experimentally obtained data. Two different heterogeneous structures - regular (periodic) and stochastic, were studied. Frequency dependencies of the complex dielectric permittivities of the materials of the constituent phases of the composites were measured and were used as input for computer modelling together with their known geometrical parameters. Calculations were based on the effective media approach, and the associated field problem was solved numerically using the finite-volume method and the finite-element method. The results of the measurements and the computations of the effective complex permittivities of the composite materials are compared and are analysed.
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| 6. |
- Serdyuk, Yuriy, 1963, et al.
(författare)
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Electrical breakdown in nonuniformly heated gases and the upper temperature limit of the applicability of Paschen’s law
- 2000
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Ingår i: High Temperature. - 1608-3156 .- 0018-151X. ; 38:3, s. 335-343
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Tidskriftsartikel (refereegranskat)abstract
- The electrical breakdown of nonuniformly heated gas-discharge gaps with a uniform electric field at temperatures of 1200–3600 K is studied experimentally. It is found that the thermionic emission from the cathode has an effect on the breakdown parameters. This effect starts manifesting itself at the critical density of the emission currentJcr ∽ 10−8 A/cm2 attained in experiments with a tungsten cathode at a temperatureTCT ∼ 1700 K. The increase of the cathode temperature to -2200 K results in a decrease of the breakdown voltageUbr by more than an order of magnitude due to the thermionic emission. The heating of the anode to a temperature of up to 3600 K does not result in a decrease of the breakdown voltage below the values defined by the gas density. In this case, the decrease of the values ofUbr is due only to the change of the gas density distribution along the gap length and obeys the generalized law of similarity. The existence of a critical temperatureTT is predicted, above which one should expect a drastic decrease of the breakdown voltage due to the thermal ionization of gas. The value ofTT depends on the configuration of the thermal field between the electrodes and the type of gas. In the thermal fields typical of our experimental conditions involving the heating of one of the electrodes, the critical temperature for xenon is about 4700 K. The studies were carried out in argon, krypton, and xenon.
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| 10. |
- Serdyuk, Yuriy, 1963, et al.
(författare)
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Numerical calculation of electric fields, losses and interfacial charge densities in water-treed dielectric composite structure
- 2004
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Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 61:3-4, s. 171-187
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Tidskriftsartikel (refereegranskat)abstract
- Results of the computer modeling and an analysis of electrical processes in a water-treed polyethylene (XLPE) are presented. The water-treed region is considered as a binary composite structure in frequency domain. Electric fields, energy losses and interfacial charge densities are calculated and are examined using a simplified layered model and 3D model of a real water-treed XLPE insulation. It is shown that the interfacial charges in the bulk of the composite structure build up mostly due to differences in conductive properties of the constituent phases, and the distributions of the electric fields and losses are determined also by the morphology of the water-treed region.
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