XLPE high voltage insulation; A link between DC conductivity and microstructure

Pourrahimi, Amir Masoud; Pitois, Claire; Abbasi, Amirhossein

doi:10.1016/j.polymertesting.2024.108330

Cited by 5 publications

(3 citation statements)

References 26 publications

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Section: ■ Results and Discussionmentioning

confidence: 99%

“…The former is obtained from the melting enthalpy ratio of semicrystallized to fully crystallized polyethylene (here −287.3 J/g). The lamella thickness is obtained from the melting point and the Thomson–Gibbs equation: , T m = T m 0 true( 1 − 2 σ normale l normalΔ h true) where T m is the melting temperature, T m 0 is the melting temperature of the infinite lamella (here 414.6 K), σ e is the surface free energy (here 7 × 10 –2 J/m 2 ), Δ h is the melting enthalpy per unit volume (here 2.88 × 10 8 J/m 3 ), and l is the lamella thickness.…”

Section: Resultsmentioning

confidence: 99%

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Enhanced DC Breakdown Strength of XLPE via Denser Cross-Linking Network Formation with Liquid Polybutadiene

Sui,

Xu,

Ahmed

et al. 2024

Macromolecules

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Due to the increased voltage in high-voltage direct current (HVDC) cables, the insulation layer thickens, posing challenges in removing cross-linking byproducts, which influences the electrical properties of cross-linked polyethylene (XLPE). This research aimed to enhance DC breakdown properties while reducing the cross-linker dosage and maintaining the cross-linking degree. Liquid polybutadiene (LPB) is incorporated into the base resin, namely, low-density polyethylene (LDPE), and cross-linked at lower cross-linker level. The results show that after the addition of 1.5 phr LPB, the DC breakdown strength of XLPE increased by at least 15.13%. The heat elongation rate decreased from 138.61% to 35.00%, indicating denser cross-linking network formation. Infrared spectrum analysis indicated the creation of new cross-links by additional vinyl groups from LPB and the suppression of ineffective cross-linking reactions. Positron annihilation lifetime spectroscopy revealed a decrease in the average radius of freevolume holes from 0.322 to 0.319 nm at 30 °C, when the cross-linking density changed from 6284 to 5157 g/mol. Based on the freevolume breakdown theory, the elevated breakdown strength can be attributed to the smaller free-volume holes. This research presents a novel strategy for developing improved XLPE and offers a solution to compromised electrical properties affected by crosslinking byproducts.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Enhanced DC Breakdown Strength of XLPE via Denser Cross-Linking Network Formation with Liquid Polybutadiene

Sui,

Xu,

Ahmed

et al. 2024

Macromolecules

View full text Add to dashboard Cite

show abstract

“…Recently, the eccentricity fault owing to the deformation of insulation was frequently found in non-cross-linked thermoplastic power cables, resulting in a distorted electrical field and final breakdown failures. In addition to the eccentricity fault results from heat shock at 250 °C caused by short-circuit faults, creep is thought to be another long-term reason due to the high operating temperatures . According to previous studies, the microstructures of PP are found to be particularly crucial for its creep performance, especially for PP-based blends or copolymers with elastomers. , The unrestricted heterogeneous components are deformed by external stress due to the poor compatibility between phases, which finally leads to the relatively poor resistance against creep.…”

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confidence: 99%

Largely Improved Creep Resistance and Thermal-Aging Stability of Eco-Friendly Polypropylene High-Voltage Insulation by Long-Chain Branch-Induced Interfacial Constraints

Wu,

Sui,

Yang

et al. 2024

ACS Macro Lett.

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Polypropylene (PP)-based composites have attracted numerous attention as a replacement of prevailing cross-linked polyethylene (XLPE) for high-voltage insulation due to their ease of processing, recyclability, and excellent electrical performance. However, the poor resistances against high-temperature creep and thermal aging are obstacles to practical applications of PP-based thermoplastic high-voltage insulation. To address these problems, in this Letter, we synthesized an impact polypropylene copolymer (IPC) containing multifold long-chain branched (LCB) structures in phases, especially the interfaces between the PP matrix and the rubber phase. The results indicated that the structural stability of LCBIPC was significantly enhanced under extreme conditions. In comparison to IPC (without LCB structures), 24.1% less creep strain and 75.2% less unrecoverable deformation are achieved in LCBIPC at 90 °C. In addition, the thermal aging experiments were performed at 135 °C for 48 and 88 days for IPC and LCBIPC, respectively. The results show that the resistance against thermal aging was also enhanced in LCBIPC, which showed a 133% longer thermal aging life compared to IPC. Further results revealed that the interfacial layer between the PP matrix and the rubber phase was constructed in LCBIPC. The two phases are tightly linked by chemical bonds in LCB structures, leading to enforced constraints of the rubber phase at the micro level and better resistance performance against creep and thermal aging at the macro level. Evidently, the reported eco-friendly LCBIPC thermoplastic insulation shows great potential for applications in high-voltage cable insulation.

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A Review of Polyolefin‐Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products

Bjurström,

Edin,

Hillborg

et al. 2024

Advanced Materials

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This review focuses on the use of polyolefins in high‐voltage direct‐current (HVDC) cables and capacitors. A short description of the latest evolution and current use of HVDC cables and capacitors is first provided, followed by the basics of electric insulation and capacitor functions. Methods to determine dielectric properties are described, including charge transport, space charges, resistivity, dielectric loss, and breakdown strength. The semicrystalline structure of polyethylene and isotactic polypropylene is described, and the way it relates to the dielectric properties is discussed. A significant part of the review is devoted to describing the state of art of the modeling and prediction of electric or dielectric properties of polyolefins with consideration of both atomistic and continuum approaches. Furthermore, the effects of the purity of the materials and the presence of nanoparticles are presented, and the review ends with the sustainability aspects of these materials. In summary, the effective use of modeling in combination with experimental work is described as an important route toward understanding and designing the next generations of materials for electrical insulation in high‐voltage transmission.

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XLPE high voltage insulation; A link between DC conductivity and microstructure

Cited by 5 publications

References 26 publications

Enhanced DC Breakdown Strength of XLPE via Denser Cross-Linking Network Formation with Liquid Polybutadiene

Enhanced DC Breakdown Strength of XLPE via Denser Cross-Linking Network Formation with Liquid Polybutadiene

Largely Improved Creep Resistance and Thermal-Aging Stability of Eco-Friendly Polypropylene High-Voltage Insulation by Long-Chain Branch-Induced Interfacial Constraints

A Review of Polyolefin‐Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products

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