| 1. |
- Kumara, Sarath, 1979, et al.
(författare)
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Electrical Characterization of a New Crosslinked Copolymer Blend for DC Cable Insulation
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- To design reliable high voltage cables, clean materials with superior insulating properties capable of operating at high electric field levels at elevated temperatures are required. This study aims at the electrical characterization of a byproduct-free crosslinked copolymer blend, which is seen as a promising alternative to conventional peroxide crosslinked polyethylene currently used for high voltage direct current cable insulation. The characterization entails direct current (DC) conductivity, dielectric response and surface potential decay measurements at different temperatures and electric field levels. In order to quantify the insulating performance of the new material, the electrical properties of the copolymer blend are compared with those of two reference materials; i.e., low-density polyethylene (LDPE) and peroxide crosslinked polyethylene (XLPE). It is found that, for electric fields of 10–50 kV/mm and temperatures varying from 30 °C to 70 °C, the DC conductivity of the copolymer blend is in the range of 10−17–10−13 S/m, which is close to the conductivity of crosslinked polyethylene. Furthermore, the loss tangent of the copolymer blend is about three to four times lower than that of crosslinked polyethylene and its magnitude is on the level of 0.01 at 50 °C and 0.12 at 70 °C (measured at 0.1 mHz and 6.66 kV/mm). The apparent conductivity and trap density distributions deduced from surface potential decay measurements also confirmed that the new material has electrical properties at least as good as currently used insulation materials based on XLPE (not byproduct-free). Thus, the proposed byproduct-free crosslinked copolymer blend has a high potential as a prospective insulation medium for extruded high voltage DC cables.
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| 2. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Click chemistry-type crosslinking of a low-conductivity polyethylene copolymer ternary blend for power cable insulation
- 2020
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Ingår i: Polymer International. - : Wiley. - 1097-0126 .- 0959-8103. ; 69:4, s. 404-412
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Tidskriftsartikel (refereegranskat)abstract
- High-voltage direct-current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high-voltage power cable insulation - low-density polyethylene (LDPE) - is usually crosslinked with peroxides, a process that releases unwanted by-products. Hence, by-product-free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry-type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co-monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co-monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 degrees C. Instead, at 200 degrees C rapid curing is possible, leading to thermosets with a low direct-current electrical conductivity of about 10(-16) S cm(-1) at an electric field of 20 kV mm(-1) and 70 degrees C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide-cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. (c) 2019 Society of Chemical Industry
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| 3. |
- Ouyang, Yingwei, 1995, et al.
(författare)
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High-temperature creep resistant ternary blends based on polyethylene and polypropylene for thermoplastic power cable insulation
- 2021
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Ingår i: Journal of Polymer Science. - : Wiley. - 2642-4150 .- 2642-4169. ; 59:11, s. 1084-1094
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Tidskriftsartikel (refereegranskat)abstract
- The impact of a small amount of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) on the thermomechanical and electrical properties of blends comprising low-density polyethylene (LDPE) and isotactic polypropylene (PP) is investigated. SEBS is found to assemble at the PP:LDPE interface as well as within isolated PP domains. The addition of 10 wt% SEBS significantly increases the storage modulus between the melting temperatures of the two polyolefins, 110 and 160°C, and results in improved resistance to creep during both tensile deformation as well as compression. Furthermore, the ternary blends display a very low direct-current (DC) conductivity as low as 3.4 × 10 S m at 70°C and 30 kV mm , which is considerably lower than values measured for neat LDPE. The here presented type of ternary blend shows potential as an insulation material for high-voltage direct current power cables.
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| 4. |
- Ouyang, Yingwei, 1995, et al.
(författare)
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Highly insulating thermoplastic blends comprising a styrenic copolymer for direct-current power cable insulation
- 2022
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Ingår i: High Voltage. - : Institution of Engineering and Technology (IET). - 2397-7264. ; 7:2, s. 251-259
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Tidskriftsartikel (refereegranskat)abstract
- The impact of the composition of blends comprising low-density polyethylene (LDPE), isotactic polypropylene (PP) and a styrenic copolymer additive on the thermomechanical properties as well as the direct-current (DC) electrical and thermal conductivity is investigated. The presence of 5 weight percent (wt%) of the styrenic copolymer strongly reduces the amount of PP that is needed to enhance the storage modulus above the melting temperature of LDPE from 40 to 24 wt%. At the same time, the copolymer improves the consistency of the thermomechanical properties of the resulting ternary blends. While both the DC electrical and thermal conductivity strongly decrease with PP content, the addition of the styrenic copolymer appears to have little influence on either property. Evidently, PP in combination with small amounts of a styrenic copolymer not only allows to reinforce LDPE at elevated temperatures but also functions as an electrical conductivity-reducing additive, which makes such thermoplastic ternary formulations possible candidates for the insulation of high-voltage power cables.
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| 5. |
- Ouyang, Yingwei, 1995
(författare)
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Novel Thermoplastic Material Concepts for High Voltage Cable Insulation - Engineering Immiscible Blends for a Sustainable Future
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To cope with our growing demand for energy in a sustainable way, efficient long-distance power transmission via high voltage direct current (HVDC) cables is crucial – these cables facilitate the integration of renewable energy into our power networks. For reliable and efficient power transmission, underground and undersea cables require robust insulation materials that possess a high level of mechanical integrity, a low direct-current (DC) electrical conductivity and a high thermal conductivity at the elevated temperatures experienced during cable operation. There is growing interest in thermoplastic materials that fulfill these requirements since thermoplastics offer the possibility for mechanical recycling by melt-reprocessing, and allow for more energy efficient cable production. In this thesis, it is shown that thermoplastic blends of low-density polyethylene (LDPE) and isotactic polypropylene (iPP) can be engineered towards HVDC cable insulation applications despite the immiscibility between LDPE and iPP. Reactive compounding was explored as a strategy for compatibilising iPP and LDPE, resulting in a material concept that exhibited good thermomechanical properties while maintaining low DC electrical conductivity and thermoplasticity. Blends comprising iPP, LDPE and a styrenic copolymer were also investigated. This led to another thermoplastic material concept where the blend composition could be tuned to simultaneously attain appropriate mechanical stiffness, DC electrical conductivity and thermal conductivity. Further, the addition of aluminium oxide nanoparticles was found to reduce the already low DC electrical conductivity of such blends. The novel material concepts described in this thesis may facilitate the design of thermoplastic insulation materials for HVDC cables of the future.
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| 6. |
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| 7. |
- Ouyang, Yingwei, 1995
(författare)
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Thermoplastic Insulation for High Voltage Cables
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High voltage direct current (HVDC) cables that seamlessly integrate renewables have an important contribution to the modern world’s efforts towards a more sustainable future. Extruded HVDC cables that efficiently and reliably transport electricity require robust insulation materials with good thermomechanical and dielectric properties. Peroxide-crosslinked polyethylene (XLPE) has been the conventional insulation material for extruded HVDC cables. However, peroxide crosslinking releases by-products that need to be removed, necessitating an expensive and time-consuming degassing procedure. Furthermore, XLPE is a thermoset material, which cannot be recycled by re-extrusion. Thermoplastic materials are therefore sought after as more sustainable material alternatives for HVDC cable insulation. Blends that contain isotactic polypropylene (iPP) are of great interest due to the thermomechanical reinforcement that its high melting crystals can offer. However, iPP alone is too brittle. Blends comprising iPP and softer components like polyethylene could give properties desired in cable insulation, but the incompatibility between iPP and LDPE must be considered. This thesis presents reactive compounding as a strategy to form PP–PE-type copolymers in-situ in a recyclable ternary blend comprising an ethylene-glycidyl methacrylate copolymer, a maleic anhydride-grafted polypropylene and low density polyethylene (LDPE). The material demonstrated excellent thermomechanical and DC dielectric properties, reflecting this novel strategy as a promising one for the design of recyclable insulation materials for future HVDC cables.
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| 8. |
- Soroudi, Azadeh, 1979, et al.
(författare)
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Highly insulating thermoplastic nanocomposites based on a polyolefin ternary blend for high-voltage direct current power cables
- 2022
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 14:21, s. 7927-7933
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Tidskriftsartikel (refereegranskat)abstract
- Octyl-silane-coated Al2O3 nanoparticles are found to be a promising conductivity-reducing additive for thermoplastic ternary blends comprising low-density polyethylene (LDPE), isotactic polypropylene and a styrenic copolymer. The ternary blend nanocomposites were prepared by compounding the blend components together with an LDPE-based masterbatch that contained the nanoparticles. The nanoparticles did not affect the superior stiffness of the ternary blends, compared to neat LDPE, between the melting temperatures of the two polyolefins. As a result, ternary blend nanocomposites comprising 38 wt% polypropylene displayed a storage modulus of more than 10 MPa up to at least 150 °C, independent of the chosen processing conditions. Moreover, the ternary blend nanocomposites featured a low direct-current electrical conductivity of about 3 × 10−15 S m−1 at 70 °C and an electric field of 30 kV mm−1, which could only be achieved through the presence of both polypropylene and Al2O3 nanoparticles. This synergistic conductivity-reducing effect may facilitate the design of more resistive thermoplastic insulation materials for high-voltage direct current (HVDC) power cables.
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