| 1. |
- Andersson, Mattias, 1985, et al.
(författare)
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Invariant Dielectric Strength upon Addition of Low Amounts of HDPE to LDPE
- 2016
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; , s. 711-714
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Konferensbidrag (refereegranskat)abstract
- Blending of polyethylenes permits to combine the superior mechanical properties of high-density material with the higher purity that is associated with low-density resins. Mixing different polyethylene architectures offers a lot of advantages, but for electrical applications it is important that there is no detrimental effect on the resulting dielectric strength. Here, the nanostructure of crosslinked blends that comprise low-and high-density polyethylene (LDPE and HDPE) is explored. Despite the presence of higher-melting lamellae the formation of electrical trees under alternating current (AC) conditions is found to be invariant for the investigated HDPE content of 1 to 10 wt%. This observation suggests that the use of polyethylene blends is feasible for AC electrical applications.
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| 2. |
- Chen, Xiangrong, 1982, et al.
(författare)
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AC and DC Pre-stressed Electrical Trees in LDPE and its Aluminum Oxide Nanocomposites
- 2016
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-4135 .- 1070-9878. ; 23:3, s. 1506-1514
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Tidskriftsartikel (refereegranskat)abstract
- Resistance of pure low density polyethylene (LDPE) and its aluminum oxide nanocomposites (up to 3.0 wt%) to degradation by electrical treeing under AC stress and DC pre-stress is analyzed. The experiments were carried out on wire-plane electrode specimens before and after exposure to thermal and DC electro-thermal ageing at 80 °C. The obtained results showed enhanced resistance of the nanocomposites to electrical tree inception under AC stress and the tree inception voltage (TIV) increased with nanoparticles content. It has been shown that there was an improved partial discharge (PD) resistance in the nanocomposites compared to the unfilled LDPE. The results also showed that the AC TIV in the nanocomposites consistently increased with the ageing and especially the DC electro-thermally aged specimens had about 30% higher the AC TIV as compared to the unaged material. This effect is attributed to significantly reduced mobility of charge carriers in the nanocomposites. The DC pre-stressed electrical trees generated in the investigated materials were of filamentary-branch structure and the branch channels content increases with the addition of nanoparticles. The mean tree number of the DC pre-stressed electrical trees decreased in the LDPE and its nanocomposites while the mean maximum tree length increased with the ageing treatments. It is postulated that material recrystallization and a very high electric field level on the wire electrode during the DC pre-stressed electrical tree test are the main reasons for the observed effects.
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| 3. |
- Chen, Xiangrong, 1982, et al.
(författare)
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Electrical Treeing Behavior at High Temperature in XLPE Cable Insulation Samples
- 2015
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 22:5, s. 2841-2851
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on investigations aiming to understand the behavior of electrical trees formed in XLPE cable insulation at elevated temperatures. Samples cut from a real high voltage cable equipped with an embedded electrode system and composed of a needle separated by 2 mm from counter electrode were used. The temperature was varied between 50 and 90 C and the range of voltage changed between 9 and 18 kV. The electrical treeing process was followed by means of microscopic observation from the moment of initiation until the leading branches connected the counter electrode and partial discharge (PD) activity was monitored simultaneously. The shape and fractal dimension of the resulting trees were analyzed. It was found that temperature and voltage level had pronounced effect on the process of electrical tree formation. At lower voltages different type of trees could be formed, whereas at higher voltages branch trees dominated. Increase of test temperature reduced the time for tree initiation, whereas the tree growth time was less affected, except for the lowest voltage level at which the slowest tree development was observed at the highest test temperature. It is postulated that the impeding effect of elevated temperature on tree growth is due to a change of tree channel sidewall conductivity, whereas the observed reduction of tree initiation time with the increase of temperature and voltage level is attributed to lowering of the threshold energy for damage at higher temperature as well as increasing of the injection current at higher voltage level.
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| 4. |
- Chen, Xiangrong, 1982, et al.
(författare)
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Electrical Treeing Behavior of DC and Thermally Aged Polyethylenes Utilizing Wire-Plane Electrode Geometries
- 2014
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 21:1, s. 42-52
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents electrical treeing behavior in low density polyethylene (LDPE) and cross-linked polyethylene (XLPE) after exposure to thermal and DC electro-thermal ageing. Both the ageing and the treeing tests were performed by means of two different types of test objects with wire-plane electrode geometry. One type of the tested objects contained only wire electrode of 10 µm diameter, whereas in the other type the wire electrode was attached through a semiconducting tab. The ageing was performed at 80°C with and without 10 kV DC voltage of both polarities connected to the wire and lasted up to 800 hours. The AC electrical treeing tests were applied afterwards for detecting changes of material properties after the ageing. The results showed that the electrical tree inception voltage consistently decreased with increasing time of thermal exposure, whereas the applied DC electric stress had a negligible effect on the observed behavior. Similar effects were found in both the tested materials (LDPE and XLPE) though the object type also influenced the results. For the objects with semiconducting tab, a higher level of the scale parameter was registered because of shielding effect of the tab on the electric field strength at the wire electrode. It also yielded less number of trees growing in parallel at the electrode. The dominant effect of thermal stress on the ageing of LDPE was elucidated by using various analytical techniques, like differential scanning calorimetry, infrared spectroscopy, inductively coupled plasma optical emission spectrometry and oxidation induction time, and it is believed to mainly affect antioxidant content in the test objects.
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| 5. |
- Chen, Xiangrong, 1982, et al.
(författare)
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Investigation of Temperature Effect on Electrical Trees in XLPE Cable Insulation
- 2012
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. - 9781467312509 ; 2, s. 612-615
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Konferensbidrag (refereegranskat)abstract
- In this paper, combined with the methods of real-time microscopic digital imaging and partial discharge (PD) continuous measurements, the effect of temperature on electrical tree propagation and PDs characteristics in XLPE cable insulation was investigated using an embedded needle electrode arrangement over a range of applied voltages from 9 to 15 kV rms. The temperature of the experiments varied from 10 C up to 70 C, which lay within the rated operating temperature range of XLPE cables. The results obtained show that temperature has dominant effect on electrical tree shapes and growth time. As the electrical tree shapes at lower voltages are influenced by the change of tree channel conductivity, this process appeared to be accelerated greatly by increase of experimental temperature. The tree growth time at higher voltages was decreased at higher temperatures due to the change of material morphology and it was accompanied by intensive PD activity.
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| 6. |
- Chen, Xiangrong, 1982, et al.
(författare)
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Nonlinear Time Series Analysis of Partial Discharges in Electrical Trees of XLPE Cable Insulation Samples
- 2014
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-4135 .- 1070-9878. ; 21:4, s. 1455-1461
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an investigation into the nonlinear dynamics characteristics of the partial discharge (PD) sequence measured during the propagation of typical electrical trees in XLPE cable insulation. Calculation of the correlation dimension and the largest Lyapunov exponent from the PD sequence is used to illustrate the nonlinear characteristics of the PD behavior in the electrical tree growth. The results provide strong evidence for the existence of deterministic chaos in the PD phenomenon of electrical trees, where the correlation dimension and the largest Lyapunov exponent are related with the PD activity of the tree growth, rather than a presence of random stochastic process. The fluctuating correlation dimension of the PD sequence during the branch-pine tree growth is associated with the transition of PD patterns and the change of the channel conductivity of the tree structure. It is also found that the nonlinear dynamics characteristics of the PD sequence are influenced by the applied voltage, the channel conductivity and the electrical tree shape. A possible mechanism is presented for the formation of different chaotic extents of typical electrical trees in XLPE cable insulation.
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| 7. |
- Chen, Xiangrong, 1982, et al.
(författare)
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On the Conducting and Non-conducting Electrical Trees in XLPE Cable Insulation Specimens
- 2016
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 23:1, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- The conducting and non-conducting properties of electrical trees in cross-linked polyethylene (XLPE) cable insulation are studied by means of partial discharge (PD) measurement, optical microscope, confocal Raman microprobe spectroscopy and scanning electron microscopy (SEM). Specimens equipped with an embedded electrode system and constituted of a needle separated by approximately 2 mm from the counter electrode were utilized. Various types of electrical trees were produced at a range of voltage levels from 9 to 15 kV. It was found that the electrical trees grown at low voltage levels exhibited very different electrical properties from those grown at higher voltage levels. Branch-pine trees were formed at the low voltage conditions, displaying buildup of conducting main channels composed of disordered graphitic carbon deposited on the tree sidewalls. The average domain of the graphitic residues was estimated at the range of 8-8.4 nm in size, which resulted in a sufficient channel conductivity to suppress the PD activity within the main tree channels and caused growth of the pine structure. The branch trees, grown at higher voltage levels, showed typical characteristics of non-conducting trees, in which continuous discharges eroded the tree sidewalls and the observed intensity of fluorescence decreased evidently with the distance from the needle electrode to the tree tip. The bush trees at high voltage levels also showed the non-conducting characteristics. However, some carbonized residues were formed locally in them near the needle electrode, which can be connected to the long and intensive discharge activity during the tree growth.
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| 8. |
- Chen, Xiangrong, 1982, et al.
(författare)
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Study on conducting characteristics of electrical trees in cross-linked polyethylene cable insulation
- 2012
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Ingår i: Wuli Xuebao/Acta Physica Sinica. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 61:8, s. Art. no. 087701-
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Tidskriftsartikel (refereegranskat)abstract
- The conducting characteristics of two typical electrical trees in cross-linked polyethylene (XLPE) cable insulation are studied by a combination of optical microscopy observation, partial discharge measurement and con-focal Raman spectroscopy analysis. Although they are grown under similar conditions, these two trees display very different shapes. One is a typical branch-pine tree grown at 9 kV, and the other is a branch tree grown at 11 kV. The growth and the partial discharge regularities show obvious differences. The disordered graphitic carbon is condensed in the main tree channels of the branch-pine tree. From the relative intensity of the graphitic carbon G band to D band, the graphitic domain is estimated to be about 8 nm in size. The tree channel resistance per unit length is less than 10 Ω· μm-1, which is sufficient to prevent the partial discharge from developing within the tree structure. The branch-pine tree shows the features of the conducting tree. The fluorescence background is observed in the channels of branch tree, which shows the existence of the products of the material degradation, but no disordered graphitic carbon is observed in these tree channels. These tree channels display obvious non-conducting characteristics, which is not sufficient to prevent the continuous effect of the partial discharges. Finally, a single channel growth model is proposed for the conducting and non-conducting trees grown in XLPE cable insulation. Based on the equivalent circuit theory, the growth mechanisms of the two trees with different conducting characteristics in XLPE cable insulation are discussed.
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| 9. |
- Mantsch, Adrian Razvan, 1983, et al.
(författare)
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The Effect of DC Electro-thermal Ageing on Electrical Treeing in Polyethylene
- 2013
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Ingår i: 23rd NORDIC INSULATION SYMPOSIUM. ; , s. 29-32
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Konferensbidrag (refereegranskat)abstract
- Electrical treeing is among the main mechanisms responsible for electric breakdown in polymeric high voltage cables. In this paper, electrical treeing in electro-thermally aged low density polyethylene (LDPE) was evaluated by means of a real-time microscopic detection system. A wire – plane electrode test object with semiconducting tab was used in the study. The ageing was performed at a constant temperature of 80°C and an applied DC voltage of 10 kV of both polarities and lasted from 100 up to 800 hours. For testing the resistances to electrical treeing, tests were performed by applying 50 Hz AC voltage at a ramping speed of 0.5 kV/s. The obtained experimental results showed that mainly the thermal component of the ageing had an influence on electrical treeing parameters, namely on the initiation voltage as well as the shape and occurrence frequency of the trees. With an increase of the ageing time, the tree inception voltage gradually decreased.
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| 10. |
- Murdany, Deni, 1983, et al.
(författare)
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Electrical treeing in polyethylene-alumina-filled nanocomposites for HVDC applications
- 2015
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Ingår i: Proceedings - 5th International Conference on Electrical Engineering and Informatics. - 9781467373197 ; , s. 213-216
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Konferensbidrag (refereegranskat)abstract
- Electrical tree formations under DC pre-stress followed by an application of voltage pulses of opposite polarities were observed in low density polyethylene and its nanocomposite filled with 1.0 wt% and 3.0 wt% alumina nanoparticles. A special wire-plane electrode geometry were manufactured for the test. The obtained experimental results indicate that the addition of the nanoparticles has a positive impact on the resistance to electrical treeing. In addition to the reported above results, a thermal ageing and electro-thermal experiment is presently being conducted and the results comparing the treeing behavior after it will also be presented.
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