scholarly journals Improved DC Dielectric Performance of Photon-Initiated Crosslinking Polyethylene with TMPTMA Auxiliary Agent

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3540 ◽  
Author(s):  
Peng Qiu ◽  
Jun-Qi Chen ◽  
Wei-Feng Sun ◽  
Hong Zhao
Keyword(s):  
Space Charge ◽  
First Principles ◽  
First Principles Calculations ◽  
Charge Accumulation ◽  
Depolarization Current ◽  
Trapping Mechanism ◽  
Crosslinking Process ◽  
Deep Traps ◽  
Molecular Group ◽  
Dielectric Performance

To achieve high direct current (DC) dielectric performance of crosslinked polyethylene (XLPE) applied for insulated cable, the auxiliary crosslinking agent of trimethylolpropane trimethacrylate (TMPTMA) is employed in photon-initiated crosslinking process to the present polar-molecular group which will introduce deep traps for charge carriers. The space-charge accumulation and electrical conductance of XLPE are observably suppressed due to the deep traps deriving from the TMPTMA crosslinkers that are chemically connecting (grafted onto) polyethylene molecules. Thermally stimulated depolarization current tests and first-principles calculations consistently demonstrate a trapping mechanism of impeding charge injection and carrier transport in XLPE with TMPTMA crosslinkers. The characteristic cyclic anhydrides with coupled carbonyl groups are used as auxiliary crosslinkers to promote crosslinking efficiency and provide polar groups to polyethylene molecules which can be effectively fulfilled in industrial cable production. The results of infrared spectroscopy show that the auxiliary crosslinkers have been successfully grated to polyethylene molecules through the UV-initiation process. The space-charge characteristics achieve a significant improvement consistent with the theoretical estimation that deeper electronic traps can be introduced by auxiliary crosslinker and will consequently suppress space-charge accumulation through a trapping mechanism. Meanwhile, the conductivity of XLPE observably increases after using TMPTMA auxiliary crosslinkers at various temperatures of cable operation. The first-principles calculations also demonstrate that substantial electronic bound states have been introduced at the band edge of polyethylene molecules crosslinked by TMPTMA, leading to reduction in electrical conductivity. On the advantage of ameliorating DC dielectric performance by way of UV-initiated crosslinking process, the present research suggests a substantial strategy in XLPE cable industrial productions.

Surface defect chemistry of Y-substituted and hydrated BaZrO3 with subsurface space-charge regions

2016 ◽  
Vol 4 (19) ◽  
pp. 7437-7444 ◽  
Author(s):  
Jonathan M. Polfus ◽  
Tor S. Bjørheim ◽  
Truls Norby ◽  
Rune Bredesen
Keyword(s):  
Surface Layer ◽  
Space Charge ◽  
Space Charge Region ◽  
First Principles ◽  
Surface Defect ◽  
Surface Defects ◽  
Defect Chemistry ◽  
First Principles Calculations ◽  
Proton Conducting ◽  
Charged Species

First-principles calculations were utilized to elucidate the complete defect equilibria of surfaces of proton conducting BaZrO3, encompassing charged species adsorbed to the surface, defects in the surface layer as well as in the subsurface space-charge region and bulk.

Defect chemistry of a BaZrO3 Σ3 (111) grain boundary by first principles calculations and space–charge theory

2012 ◽  
Vol 14 (35) ◽  
pp. 12339 ◽  
Author(s):  
Jonathan M. Polfus ◽  
Kazuaki Toyoura ◽  
Fumiyasu Oba ◽  
Isao Tanaka ◽  
Reidar Haugsrud
Keyword(s):  
Grain Boundary ◽  
Space Charge ◽  
First Principles ◽  
Defect Chemistry ◽  
First Principles Calculations

scholarly journals Interplay between H2O and CO2 coadsorption and space-charge on Y-doped BaZrO3 surfaces

2018 ◽  
Vol 6 (48) ◽  
pp. 24823-24830 ◽  
Author(s):  
Jonathan M. Polfus ◽  
Jing Yang ◽  
Bilge Yildiz
Keyword(s):  
Surface Chemistry ◽  
Space Charge ◽  
First Principles ◽  
Crucial Role ◽  
Surface Defects ◽  
First Principles Calculations

Crucial role of coadsorption, surface defects and subsurface space-charge on the surface chemistry of oxides is demonstrated by first-principles calculations.

scholarly journals Space Charge Characteristics of Polypropylene Modified by Rare Earth Nucleating Agent for β Crystallization

Materials ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 42 ◽  
Author(s):  
Jiaming Yang ◽  
Mingze Gao ◽  
Hong Zhao ◽  
Shilin Liu ◽  
Ming Hu ◽  
...  
Keyword(s):  
Rare Earth ◽  
Space Charge ◽  
Impact Resistance ◽  
Nucleating Agent ◽  
Mechanical Analysis ◽  
Mechanical Relaxation ◽  
Charge Accumulation ◽  
Depolarization Current ◽  
High Voltage Direct Current ◽  
Lamellar Crystals

Compared to cross-linked polyethylene, polypropylene has a thermoplastic property and the advantage of recycling. However, the poor impact resistance at low temperature and the corresponding space charge problem restrict the application of polypropylene with the extruded high voltage direct current (HVDC) cable. Sufficient introduction of the β form of the polypropylene crystal can significantly improve impact resistance at low temperatures. Although it has been widely applied in insulation engineering, the effect of β-crystal on the space charge characteristics of polypropylene has rarely been researched until now. In this paper, a rare earth nucleating agent of β-crystal is employed to modify the performance of polypropylene to investigate the effects of nucleating agent content on β-crystalline, mechanical relaxation, trap, and space charge characteristics of polypropylene. The results of differential scanning calorimeter (DSC) and X-ray diffraction (XRD) tests indicate that the relative content of β-crystal in modified polypropylene increases gradually with the increasing concentration of the nucleating agent, approaching 43.5% when the nucleating agent content has been raised to 0.2 wt %, suggesting appreciable efficiency of the nucleating agent utilized in our research. Scanning electron microscopy (SEM) is utilized to characterize the morphology of β-crystal spherulites, which illustrates that the β-spherulites are in bunchy shape, and the lamellar crystals are parallel to each other without an obvious boundary between them. The results of the space charge test demonstrate that the modified polypropylene can substantially suppress space charge accumulation, which is attributed to an increment of β-crystal content by adopting a rare earth nucleating agent. It is indicated from dynamic mechanical analysis (DMA) measurements that the enhancement of β-crystalline in modified polypropylene can distinctly increase and decrease the β and α relaxation losses, respectively, which proves that the defects in β-crystal and amorphous regions are reduced and increased respectively. Thermally stimulated depolarization current tests further confirm that the number of traps caused by defects in the β-form of polypropylene crystal declines definitely, which dominantly accounts for the suppression of space charge accumulation.

scholarly journals Influence of Temperature on Charge Accumulation in Low-Density Polyethylene Based on Depolarization Current and Space Charge Decay

Polymers ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 587 ◽  
Author(s):  
Guochang Li ◽  
Jiaxing Wang ◽  
Wang Han ◽  
Yanhui Wei ◽  
Shengtao Li
Keyword(s):  
Space Charge ◽  
Charge Trapping ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Insulation Material ◽  
Charge Accumulation ◽  
Depolarization Current ◽  
Close Link ◽  
Influence Of Temperature ◽  
Influence Of Temperature On

Temperature is one of the key factors affecting space charge accumulation in high voltage direct current (HVDC) cable insulation material. The influence of temperature on charge accumulation in low density polyethylene (LDPE) has been investigated with a combined thermally stimulated depolarization current (TSDC) method and pulsed electro-acoustic (PEA) method. The experimental results indicate that there exists a transition temperature region of charge accumulation around 50 °C. The total accumulated charges all firstly increase and then decrease with the increasing polarization temperature under three typical polarization electric fields, and they have more accumulated charges in LDPE around 50 °C. The phenomenon has a close link with the dynamic processes of charge trapping and de-trapping, which were verified by TSDC results. At room temperature, the trapped charges are difficult to release from the traps, and these homocharges near the cathode can depress the further injection of the charges. More charges can be injected from the electrodes with the increase of temperature, while the charge migration is relatively lower before 50 °C, leading to more accumulated charges. When the temperature exceeds around 50 °C, the molecular movement is accelerated which can enhance the hopping probability of charges between the adjacent traps, resulting in few accumulated charges.

scholarly journals Significantly Improved Electrical Properties of Photo-Initiated Auxiliary Crosslinking EPDM Used for Cable Termination

Polymers ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2083 ◽  
Author(s):  
Zhong-Yuan Li ◽  
Wei-Feng Sun ◽  
Hong Zhao
Keyword(s):  
Electric Field ◽  
First Principles ◽  
Electric Field Distribution ◽  
Breakdown Strength ◽  
First Principles Calculations ◽  
Carbonyl Groups ◽  
Trapping Mechanism ◽  
Polar Groups ◽  
Lower Temperature ◽  
Electrical Materials

In order to achieve high quality electrical materials for cable terminations, the crosslinked ethylene-propylene-diene monomer (EPDM) materials, with adequate breakdown strength, appropriately increased conductivity and are developed by employing auxiliary crosslinker and ultraviolet (UV) photoinitiated crosslinking technique. The characteristic cyclic anhydrides with coupled carbonyl groups are utilized as auxiliary crosslinkers to promote crosslinking efficiency and provide polar-groups to EPDM molecules in UV-initiated crosslinking processes, which can be effectively fulfilled in industrial cable production. The results of infrared spectroscopy show that the auxiliary crosslinkers have been successfully grated to EPDM molecules through UV initiation process. The conductivity of EPDM increases after individually utilizing three auxiliary crosslinkers to EPDM at various temperatures of cable operations, by which the highest conductivity has been acquired by grafting N.N-m-phenylene dimaleimide. The first-principles calculations demonstrate that some occupied local electronic-states have been introduced in the band-gap of the EPDM crosslinked by N.N-m-phenylene dimaleimide (EPDM-HAV2), which can be thermally excited from valence band to conduction band at lower temperature or in higher density, leading to augmentation in electrical conductivity. Meanwhile, the breakdown strength achieves a significant improvement in consistency with the theoretical estimation that deeper hole-traps can be introduced by auxiliary-crosslinking modification, and will consequently increase breakdown strength through the trapping mechanism of space charge suppression. in relation to the appropriately increased conductivity, in combination with persistent breakdown strength, the finite element simulations of the electric field distribution in EPDM cable terminations suggest that the effectively homogenized electric field at the root of stress cone will be realized for EPDM-HAV2. The present study offers a fundamental strategy to ameliorate EPDM materials in the application of insulated cable accessories.

scholarly journals Improved DC Dielectric Performance of -MAH/iPP/SEBS Composite with Chemical Graft Modification

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1094 ◽  
Author(s):  
Yu Zhou ◽  
Jiaming Yang ◽  
Hong Zhao ◽  
Weifeng Sun ◽  
Mingze Gao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Dielectric Properties ◽  
Space Charge ◽  
Carrier Transport ◽  
Charge Trapping ◽  
Structure Characterization ◽  
Characterization Methods ◽  
Deep Traps ◽  
Dielectric Performance ◽  
Stimulation Current

In order to achieve both high toughness and favorable dielectric properties of polypropylene materials, a styrene–butadiene–styrene block copolymer (SEBS) was employed as a toughening filler, in addition to a copolymerized polypropylene grafted by maleic anhydride (cPP-g-MAH) as a compatibilization modifier, to develop a novel isotactic polypropylene (iPP) composite (cPP-g-MAH/iPP/SEBS composite) with significantly improved direct-current (DC) dielectric performance and tenacity. The underlying physical and chemical mechanisms of modifying electric insulation were studied utilizing micro-structure characterization methods in combination with multiple thermal–mechanic–electric tests. The SEBS phase islands are uniformly distributed in the PP matrix with evidently improved dispersion due to cPP-g-MAH compatibilization. Compared with iPP, the elastic modulus of cPP-g-MAH/iPP/SEBS composites can be reduced by 58% with doubled thermal elongation, which is still superior to that of cross-linked polyethylene (XLPE), implying that the composites are qualified in terms of mechanical properties for use as power cables. The space charge accumulation and electric conduction are considerably suppressed in comparison with pure iPP and the iPP/SEBS composite. In the interest of charge-trapping characteristics modified by chemically grafting MAH, the deep traps introduced into polypropylene by grafting MAH were measured with a thermal stimulation current experiment to be 1.2 and 1.6 eV of energy level in trapping depth, verified through the first-principles electronic structure calculations with an all-electron numerical orbital scheme. It was concluded that the acquired high density of deep traps can effectively restrict the carrier transport and suppress the injection of space charge, resulting in a remarkable improvement of DC dielectric properties for the MAH grafted composites. The present work demonstrates that the cPP-g-MAH/iPP/SEBS composites are eligible to be applied to polypropylene-based high-voltage DC cables due to their excellent DC insulation performance, together with the appropriate mechanical properties.

scholarly journals Practical Notes on the Measurement and Interpretation of Thermally Stimulated Discharge Currents in Biaxially Oriented Polypropylene

2019 ◽  
pp. 64-69
Author(s):  
Ilkka Rytöluoto ◽  
Minna Niittymäki ◽  
Kari Lahti
Keyword(s):  
Glass Transition ◽  
Dielectric Properties ◽  
Space Charge ◽  
High Field ◽  
Short Term ◽  
Depolarization Current ◽  
Deep Traps ◽  
Biaxially Oriented Polypropylene ◽  
Oriented Polypropylene ◽  
Thermally Stimulated Depolarization

The measurement and interpretation of high-field thermally stimulated depolarization current (TSDC) of capacitor-grade biaxially oriented polypropylene (BOPP) films are investigated in order to facilitate the derivation of trap parameters. Two main relaxations associable with the glass transition and detrapping of space charge from deep traps are observed, and their dependence on the polarization/depolarization conditions are studied. The complex bipolar nature of the space charge relaxation makes the derivation of trap parameters challenging. Lastly, a brief attempt is made to correlate the TSDC features with morphology and other short-term dielectric properties.

Electronic Structure and X-ray Absorption Spectra of Rutile TiO2 Using First-Principles Calculations

2014 ◽  
Vol 52 (12) ◽  
pp. 1025-1029
Author(s):  
Min-Wook Oh ◽  
Tae-Gu Kang ◽  
Byungki Ryu ◽  
Ji Eun Lee ◽  
Sung-Jae Joo ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Absorption Spectra ◽  
First Principles ◽  
First Principles Calculations ◽  
Rutile Tio2 ◽  
X Ray ◽  
X Ray Absorption
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