| 1. |
- Alam, Shahid, 1986, et al.
(author)
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Effect of Interfaces on Surface Potential Decay on Double Layered HTV Silicone Rubber Samples
- 2016
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In: Proceedings of International Conference on Dielectrics. - 9781509028030 ; 1, s. 309-312
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Conference paper (peer-reviewed)abstract
- Interfaces between materials constituting composite HVDC insulation systems are typically associated with abrupt changes of the materials’ dielectric properties, which cause accumulation of interfacial charges. These may affect various processes in the insulation system, including dynamics of charge transport and electric field distribution as well as its flashover performance. In the present study, the influence of macroscopic interfaces between layers made of high temperature vulcanized silicone rubbers on surface potential decay characteristics is analyzed. It is shown by comparing results of measurements on single and double layered samples that the rate of the potential decay may be significantly changed (increased or reduced) depending on how the layered structure is designed. The performed analyses show that the observed features cannot be explained by means of classical Maxwell-Wagner model and introducing additional charges at the investigated interface is necessary to successfully model the experimental data. The presented discussion concentrates on defining possible sources of such interfacial charges.
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| 2. |
- Alam, Shahid, 1986, et al.
(author)
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Field-dependent electric conductivities of silicone rubbers deduced from measured currents and surface potential decay characteristics
- 2019
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In: International Journal of Polymer Analysis and Characterization. - 1563-5341 .- 1023-666X. ; 24:1, s. 54-62
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Journal article (peer-reviewed)abstract
- Measurements of DC electric conductivities of four types of silicone rubber-based polymers for use in high voltage insulation systems of power components are reported. The field dependences of the conductivities obtained by two different techniques, namely by utilizing steady-state currents through materials’ samples placed between metallic electrodes and by employing surface potential decay characteristics in an open circuit configuration, are compared and discussed. It is shown that the surface potential decay technique allows for a wider range of electric field strength and reduces the time span of the measurements.
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| 3. |
- Alam, Shahid, 1986, et al.
(author)
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Potential Decay on Silicone Rubber Surfaces Affected by Bulk and Surface Conductivities
- 2015
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In: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 22:2, s. 970-978
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Journal article (peer-reviewed)abstract
- A decay of electric surface potential on a pre-charged gas-solid interface involves several charge transport processes and each of them may become dominant under certain environmental conditions (temperature, pressure, humidity). In the present paper, surface potential decay on flat samples of different kinds of silicone rubber used in HVDC applications is analyzed at reduced pressures of ambient air that allows for minimizing the involvement of the gas phase, i.e. surface charge neutralization by gas ions. Effects imposed solely by bulk and surface conduction in the solid material are studied experimentally and by means of computer simulations. The results allow for evaluating threshold values of volume and surface electric conductivities at which these mechanisms become most essential. Field dependent bulk conductivities are deduced from the surface potential decay characteristics obtained for the studied materials.
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| 4. |
- Bagheri, B., et al.
(author)
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Comparsion study of different simulation codes for positive streamers
- 2017
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In: Proceedings of the International Conference on Phenomena in Ionized Gases (ICPIG).
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Conference paper (other academic/artistic)abstract
- For streamer simulations a range of computational models have been developed by various groups for various purposes. These models differ in dimensionality (2D, 3D), model type (particle, fluid or hybrid approach and further differentiation), their numerical implementation, type of grid and its refinement, and their spatial/temporal discretization. The aim of the present study is to benchmark the results of different simulation codes for axisymmetric single positive streamers in air at 1 bar and 300 K using a fluid model.
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| 5. |
- Bozhko, Igor, et al.
(author)
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Determination of Energy of a Pulsed Dielectric Barrier Discharge and Method for Increasing Its Efficiency
- 2017
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In: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 45:12, s. 3064-3069
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Journal article (peer-reviewed)abstract
- A methodology for accurate determination of energy released in a unipolar impulse dielectric barrier discharge is proposed and verified utilizing experimental data. In theexperiments, the discharge was initiated in air under atmospheric pressure in a coaxial chamber with glass dielectric barrier located on the cathode by applying voltage pulses with the slew rate of ∼3e11 V/s. It is shown that the energy released in the discharge is defined by the charge accumulated on the dielectric barrier before application of a successive voltage pulse and the magnitude of the remaining barrier voltage is dependent on many factors, in particular, repetition frequency of the discharge pulses, conditions and material of the barrier, impedance of the external electrical circuit, etc. It is demonstrated that the effective discharging of the barrier can be achieved by introducing a magnetic switch, which is essentially a nonlinear inductance connected in parallel to the discharge gap. The use of the switch allows for increasing the discharge efficiency in ∼30% and provides a way for correct evaluations of its energy.
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| 6. |
- Chen, Xiangrong, et al.
(author)
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Surface Potential Decay on LDPE and its Nanocomposites
- 2017
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In: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; 2017-October, s. 485-488
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Conference paper (peer-reviewed)abstract
- To elucidate capabilities of nanocomposites in a full extend, deep understanding of various physical processes induced by electric fields in the bulk and on surfaces of the materials is needed. This paper reports an investigation of surface potential decay on low-density polyethylene and its mixtures with Al2O3 and MgO nanofillers. Samples of two groups materials with various thicknesses prepeared using different manufacturing processes were used in the study. The samples were pre-charged by negative corona and surface potentials were measured by a non-contact technique at room temperature. The obtained results showed that the addition of nanofillers remarkably slowed down the potential decay process irrespectively of film thicknesses and fabrication processes. This is attributed to the significantly lower conductivities of LDPE nanocomposites as compared to pure material. Moreover, the conductivities of the filled materials exhibited strong electric field dependences. It is postulated that the effect can be related to the increased trap energy in the nanocomposites.
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| 7. |
- Doedens, Espen, 1988, et al.
(author)
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Local surface field- and charge distributions and their impact on breakdown voltage for HVDC cable insulation
- 2019
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Conference paper (other academic/artistic)abstract
- Abstract. The surface topography on material interfaces plays a crucial role in performance of HVDC cable systems. In this work, the texture of interfaces was analyzed and its impact on electric field distributions at the surface was simulated. It was found that the effect of roughness and field dependent bulk conductivity of the insulation on the field distribution is associated with significant local quantities of space charges accumulated at the surface. It is shown that charge accumulation and corresponding local electric field enhancements are the parameters defining local conduction, injection and material degradation at insulation interfaces. A correlation between simulated/calculated field distributions and ramped DC breakdown voltages on cable peelings was observed.
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| 8. |
- Hoang, Tuan Anh, 1985, et al.
(author)
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Charge transport in a double-layered enamel insulation during surface potential decay
- 2018
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In: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 25:2, s. 702-712
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Journal article (peer-reviewed)abstract
- This work presents a numerical model for studying charge dynamics during decay of pre-deposited surface charges on an enamel insulation comprising two layers of different materials. It is shown that the considered surface charge decay is dominated by charge injection from insulation surface into the bulk and the drift of injected carriers along the direction of induced electric field. These features allow for estimating charge carriers' mobilities in the studied insulation. The developed model incorporates experimental outcomes as well as the proposed effect of an internal interface between insulating layers on hindering charge transport through the bulk. The transient process of charge accumulation at the internal interface is exhibited and correlated with the well-known Maxwell-Wagner-Sillars polarization model. Contribution of charge injection at each insulation surface into the bulk to the measured potential decay is evaluated and compared.
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| 9. |
- Hoang, Tuan Anh, 1985, et al.
(author)
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Charge Transport in LDPE Nanocomposites Part I—Experimental Approach
- 2016
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In: Polymers. - : MDPI AG. - 2073-4360. ; 8:3, s. 87:1-87:19
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Journal article (peer-reviewed)abstract
- This work presents results of bulk conductivity and surface potential decay measurements on low-density polyethylene and its nanocomposites filled with uncoated MgO and Al2O3, with the aim to highlight the effect of the nanofillers on charge transport processes. Material samples at various filler contents, up to 9 wt %, were prepared in the form of thin films. The performed measurements show a significant impact of the nanofillers on reduction of material’s direct current (dc) conductivity. The investigations thus focused on the nanocomposites having the lowest dc conductivity. Various mechanisms of charge generation and transport in solids, including space charge limited current, Poole-Frenkel effect and Schottky injection, were utilized for examining the experimental results. The mobilities of charge carriers were deduced from the measured surface potential decay characteristics and were found to be at least two times lower for the nanocomposites. The temperature dependencies of the mobilities were compared for different materials.
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| 10. |
- Hoang, Tuan Anh, 1985, et al.
(author)
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Charge Transport in LDPE Nanocomposites Part II—Computational Approach
- 2016
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In: Polymers. - : MDPI AG. - 2073-4360. ; 8:4, s. 103:1-103:16
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Journal article (peer-reviewed)abstract
- A bipolar charge transport model is employed to investigate the remarkable reduction in dc conductivity of low-density polyethylene (LDPE) based material filled with uncoated nanofillers (reported in the first part of this work). The effect of temperature on charge transport is considered and the model outcomes are compared with measured conduction currents. The simulations reveal that the contribution of charge carrier recombination to the total transport process becomes more significant at elevated temperatures. Among the effects caused by the presence of nanoparticles, a reduced charge injection at electrodes has been found as the most essential one. Possible mechanisms for charge injection at different temperatures are therefore discussed.
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