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| 2. |
- Doedens, Espen, 1988, et al.
(författare)
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Considerations on the impact of material mesostructure on charge injection at cable interfaces
- 2020
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Ingår i: IEEE Electrical Insulation Magazine. - 0883-7554 .- 1558-4402. ; 36:5, s. 43-51
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Tidskriftsartikel (refereegranskat)abstract
- In many industrialized high voltage applications, polymeric insulators are subjected to high electric field strength. Examples are cables, gas-insulated switchgears (GIS), capacitors and others [1]. The difficulty in the design process of these components is to ensure and predict their long-term reliability, where one among the important aspects is prevention of local degradation phenomena. Applications in which a combination of different solid dielectric materials are utilized, such as in cable joints or dry-type terminations are also becoming more common in the strive for achieving long lasting and maintenance free components. It is thus crucial that such components are also designed for longevity and faultless operation. This involves ensuring proper physical and chemical cleanliness of the used materials, but also optimizing component geometry with regards to local enhancements of electric field.
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| 3. |
- Doedens, Espen, 1988, et al.
(författare)
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Enhanced charge injection in rough HVDC extruded cable interfaces
- 2019
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Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1558-4135 .- 1070-9878. ; 26:6, s. 1911-1918
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Tidskriftsartikel (refereegranskat)abstract
- The insulation system of an HVDC extruded cable includes a variety of different material interfaces, especially within its cable accessories. Depending on interfacial manufacturing method, different degrees of surface roughness can be found and are here assessed. Based on detailed knowledge of insulation surface roughness, this paper proposes a new approach for calculations of electrical field distributions and injection current densities at the insulation surface. It is shown that local fields at rough material interfaces can be greatly enhanced, resulting also in field reduction in other areas along the surface. These calculations also reveal a distinct field threshold for space charge injection, likely leading to formation of homocharge layer adjacent to the interface. Existence of this homocharge layer at a rough surface (density of approximately 1 C/m(3)) is confirmed by means of space charge measurements.
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| 4. |
- Doedens, Espen, 1988, et al.
(författare)
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Roughness Enhanced Charge Injection and Field Dependent Conduction Mechanisms for Bipolar Charge Transport Models
- 2020
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Ingår i: Proceedings of the 2020 IEEE 3rd International Conference on Dielectrics, ICD 2020. - 9781728189833 ; , s. 413-417
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Konferensbidrag (refereegranskat)abstract
- Extruded HVDC cable systems contain a multitude of different interface types. Physical interfaces are introduced onsite when the outer semi-conductive layer is removed prior to installing a pre-molded joint or stress-cone onto the cable end. Such interfaces are characterized by surface roughness, which can locally enhance electric field and stimulate charge injection at microscale asperities. This work studies the impact of surface roughness on charge injection by performing space charge measurements on cable peelings and evaluating the observed charge evolution with a bipolar charge model. The behavior during both polarization and depolarization stages was investigated. A unique set of conduction and injection parameters is suggested allowing for realistic interpretation of charge accumulation and decay observed in the measurements.
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| 5. |
- Doedens, Espen, 1988, et al.
(författare)
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Space Charge Accumulation at Material Interfaces in HVDC Cable Insulation Part I—Experimental Study and Charge Injection Hypothesis
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:8, s. 2005-2021
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Tidskriftsartikel (refereegranskat)abstract
- On-site installation of accessories on extruded polymeric high voltage cables in a common practice. The procedure requires the shaping of the physical interface between the cable insulation surface and the pre-molded accessory body. On such interfaces, rough surfaces should be avoided in order to limit space charge accumulation in the insulation, which affects the cable performance by reducing insulation life-time, creating conditions for local field enhancement, and, respectively, the formation of possible breakdown path e.g. by electrical treeing. Space charge measurements on cable insulation peelings were undertaken to assess the space charge injection and accumulation on interfaces with varying degrees of surface roughness in order to improve understanding on this subject. The results of the measurements confirm the hypothesis regarding the enhancement of charge injection from rough surfaces when electric field strength exceeds a certain level. The accumulated charge density in the material is shown to strongly depend on the field strength and temperature in both polarization and subsequent depolarization measurements. These results emphasize that a bipolar charge transport model that incorporates field and temperature dependencies of charge injection, trapping, detrapping, and recombination processes needs to be adopted to accurately describe the observed electric conduction phenomena.
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| 6. |
- Doedens, Espen, 1988, et al.
(författare)
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Space Charge Accumulation at Material Interfaces in HVDC Cable Insulation Part II - Simulations of Charge Transport
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:7, s. 1750-1774
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Tidskriftsartikel (refereegranskat)abstract
- Extruded high voltage direct current (HVDC) cable systems contain interfaces with poorly understood microscopic properties, particularly surface roughness. Modelling the effect of roughness on conduction in cable insulation is challenging, as the available results of macroscopic measurements give little information about microscopic charge distributions at material interfaces. In this work, macroscopic charge injection from interfaces is assessed by using a bipolar charge transport model, which is validated against a series of space charge measurements on cable peelings with different degrees of surface roughness. The electric field-dependent conduction and charge trapping effects stimulated by the injection current originating from rough surfaces are assessed. It is shown that by accounting for roughness enhanced charge injection with the parameters derived in part I of the paper, reasonable agreement between computed and measured results can be achieved at medium field strengths (10–40 kV/mm).
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| 7. |
- Doedens, Espen, 1988, et al.
(författare)
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Surface preparations on MV-sized cable ends for ramped DC breakdown studies
- 2016
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Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP. - 0084-9162. ; , s. 360-362
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Konferensbidrag (refereegranskat)abstract
- The rising demand for HVDC crosslinked polyethylene (XLPE) cable systems has put many novel products and solutions on the market within the recent years. In order to assess electrical performance of physical interfaces, DC breakdown studies of XLPE cable samples have been performed. For these samples, the surface of the XLPE in the cable ends has been modified using different techniques. Besides changing the surface preparation method, also the impact of the test conditions has been studied. A slowly ramped DC voltage has been used in order to study the breakdown characteristics for the samples. A great impact on breakdown voltage was found depending on which surface preparation was used. This highlights the fact that interfaces indeed play an important role for HVDC applications.
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