IET Nanodielectrics最新文献

In the high-humidity environment, the epoxy resin (EP) insulating materials commonly used in reactors and other equipment are prone to accelerate ageing due to the damp and hot conditions, which affects the long-term stable operation of the equipment. However, at present, the research on the blocking effect of carbon nano-modified fillers on the invasion of water molecules into the epoxy resin matrix is still unclear. Based on this, we utilised molecular dynamics simulation technology to establish six EP models of EP materials under different conditions, including water molecule invasion (WI)/non-invasion (WNI) and carbon nanomaterial modification/no modification. The carbon nano-modified materials adopted Amido-Amine Functionalised Carbon Nanotube (AFCNT) and Hydroxyl Functionalised Graphene (HFGNP). We studied the changes in key performance indicators such as relative permittivity, thermal conductivity, and glass transition temperature of six models. Eventually, it was found that the relative permittivity of the EP model significantly increased after water molecule invasion but decreased after doping with AFCNT. The thermal conductivity of the six EP models increased, and the increase in the AFCNT-EP model was the most obvious, rising by 46.65% at 300 K. The glass transition temperatures of the models all decreased, but the decrease was reduced after doping and modification with carbon nanomaterials. Overall, except for thermal conductivity, the overall performance of the EP model deteriorated to varying degrees after water molecule invasion. However, the performance deterioration trend of the model was alleviated after doping with carbon nano-modified fillers, and the performance of the model doped with AFCNT was significantly better than that of the EP model doped with HFGNP. This research can provide certain theoretical basis and technical support for the engineering application of epoxy resin materials under extreme conditions such as high humidity.

The development of a reliable, environmentally safe, and economic insulating oil for the transformer is an endless effort of the electrical industry. Mineral oil (MO), traditionally used, presents challenges including high cost, environmental impact, and limited availability. Consequently, research has shifted towards alternative solutions, aligning with green energy and environmental conservation goals. Natural ester oil has gained keen attention due to its complete biodegradability and widespread availability. This study explores alternative options, including a blend of vegetable oils (Blackseed, Castor, Flaxseed, and Mustard), aiming to enhance transformer insulation and cooling efficiency through this novel nanofluid. A novel nanofluid was synthesised using different ratios of proposed oils to produce a 300 mL sample blend of vegetable oil containing 0.03 g (0.0001 wt%) of green-synthesised SiO₂ nanoparticles (average size ∼20–30 nm). These nanoparticles were fabricated using an eco-friendly method based on Moringa leaf extract, aligning with Sustainable Development Goals (SDGs). This sample was prepared for testing and validation at the advanced High Voltage Laboratory in accordance with the IEC-60156 standard to evaluate dielectric properties. Furthermore, thermal stress was applied to the proposed samples to replicate real-time conditions. Moreover, conducted comparative analyses between a newly proposed vegetable oil-based nanofluid and conventional MO, emphasising dielectric properties, including AC and DC breakdown voltage (BDV) and stability. Results demonstrate that the eco-friendly vegetable oil-based nanofluid surpasses traditional MO by a significant 19% margin in breakdown strength. Stability assessments reveal only a 0.32% reduction in BDV for the proposed nanofluid after 6 years of simulated equivalent ageing, contrasting with a 19% reduction observed in MO. This contemporary research highlights the potential of the proposed nanofluid as a promising alternative to conventional MO, as evidenced by comprehensive testing and analysis.

The emergence of polymer nanodielectrics as suitable materials in energy storage devices highlights the importance of a deep understanding of their dielectric/electrical properties. When conductive materials are employed as nanofillers, strong interfacial polarisation and free charge carrier transport phenomena occur that both contribute to the imaginary permittivity as a peak and as a power law in the form of σ₀/(ε₀ω^s), respectively. To effectively discern and understand the two phenomena, the use of different dielectric formalisms is often preferred, that is, by the complex electric modulus M*(ω). However, when M*(ω) is employed, the free charge carrier contribution transforms into a step in M′(ω) and into a peak in M″(ω), namely, the conductivity relaxation, that can be difficult to distinguish from interfacial polarisation or dipolar effects. A general relation is proposed here to describe the non-Debye polarisation component of interfacial polarisation and non-Ohmic transport of free charge carriers in its electric modulus representation. From this relation, the conductivity relaxation can be isolated into a separate function and is shown to exhibit a symmetrical broadening that cannot be described by the semi-empirical Havriliak–Negami function when it deviates from Ohmic behaviour.

The composite cermet material based on BaTiO₃ ceramics doped with Fe was compacted using the field-assisted sintering technology (FAST). Certain oxidation of Fe and also the presence of carbon, used in sintering equipment, were detected in the sintered material. The microstructure showed well separated two components and certain porosity. Dielectric parameters were measured between 30°C and 150°C and between frequencies 100 Hz and 20 MHz. Combination of dielectric parameters at 1 MHz frequency, that is, relative permittivity 5 200, loss tangent 0.051 and thermal coefficient of capacitance 715 ppm/°C made this composite promising among the addressed category of materials. The mechanisms of polarisation and conduction and their thermal activation were discussed.

This study investigates the physical-chemical and electrochemical performances of innovative separators for Li-ion batteries based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) nanofibrous membranes. The nanofibrous mat is produced through the electrospinning process, ensuring high surface to volume (S/V) ratio and allows large-scale production under suitable conditions. The materials investigated in this work aim at overcoming some limitations specific to the commercial separators, for example, mechanical shrinkage and electrolyte uptake. This is achieved by adding nanoparticles of different types, for example, ZrO₂, SnO₂, SiO₂ at different concentrations. Results claim that nanofibrous separators improve the mechanical and thermal stability of the mat without significantly impacting its electrochemical performances. In particular, the addition of 7 wt% of ZrO₂ nanoparticles to the nanofibrous separator showed to outperform commercially available solutions (i.e., Celgard) in terms of mechanical and thermal stability exhibiting, also, electrochemical performances.

A series of innovative electron donors (D1–D6) featured both internal and external electron donors in one molecular structure were designed and synthesised. The synthesised electron donors and traditional electron donors (DIBP) were effectively reacted with titanium-based catalysts supported on magnesium chloride to obtain a series of Ziegler–Natta catalysts (Cat 0–Cat 6). Cat 0 formed by electron donor DIBP. Similarly, Cat 1 by D1, Cat 2 by D2, Cat 3 by D3, Cat 4 by D4, Cat 5 by D5 and Cat 6 by D6, respectively, which were characterised by GC-MS, ¹H (¹³C)-NMR, XPS and SEM. It is interesting that the catalytic activity of the catalysts prepared by the newly synthesised electron donor was significantly higher than that of traditional DIBP for propylene polymerisation. Under atmospheric pressure condition of propylene, the catalytic activity of Cat 3 was 112.7 g PP/(g Cat · h) and Cat 6 reached 209.2 g PP/(g Cat · h) at the same conditions, both significantly higher than that of 34.1 g PP/(g Cat · h) of Cat 0. We adopted a prealkylation strategy for the catalysts preparation, reducing the optimal aluminium titanium ratio for propylene polymerisation from 50 to 30, decreasing the amount of cocatalyst used and thus reducing the ash content in the products. During the bulk polymerisation of propylene, the activity of prealkylated Cat 3 and Cat 6 is comparable, at 79.4 kg PP/(g Cat · h), which is about 2.3 times that of Cat 0 cooperated with external electron donor C during the polymerisation processes (35.2 kg PP/(g Cat · h)), and the obtained PP isotacticity reaches over 98%. Especially, Cat 1–Cat 6 were required no external electron donor for propylene polymerisation. In addition, the theoretical ash content of the products formed by Cat 3 and Cat 6 is only 22 ppm, which is significantly lower than that of Cat 0 (133 ppm). It is expected to be used in the industrial production of ultra-clean iPP powder for capacitor films.

Metallised film capacitors consist of polymer dielectrics and electrodes which are considered as two layers. Due to the huge difference in thickness of two layers, metallisation can affect the microstructure and properties of metallised films, resulting in the bilayer structure model may not accurately describing properties. In this work, metallised films are considered as a whole rather than two layers of dielectric and electrode, whereas the process of film metallisation is regarded as a surface modification of the dielectric film. Metallised films with different metal layer thicknesses are prepared by vacuum evaporation. We investigated the dielectric, electrical and self-healing properties of metallised films. Films with thicker electrode present higher dielectric constant, conductivity, energy density and lower breakdown strength. Thinner metal layers result in less self-healing energy and better self-healing property. The difference in properties is attributed to the surface modification of dielectric films by nanoscale metallisation. Thicker electrode contributes to smaller surface roughness, which increases the polarization and charge capacity of metallised films, but also implies worse self-healing property. Surface modification provides a new perspective for researching metallised films.

As a critical component in transformer partial discharge monitoring and localisation, the output signal of the contact ultrasonic sensor is significantly influenced by its sensitivity. Consequently, field sensitivity verification of ultrasonic sensors is essential. However, field calibration is often impacted by environmental noise, and the effects of various noise types on the sensitivity calibration results remain inadequately understood. To address this issue, this paper introduces a sensitivity field calibration process tailored for ultrasonic sensors used in oil-immersed transformer. Transformer and ultrasonic sensor models are developed, and the sensor output signal is simulated using the finite element method. Noise signals of different types are superimposed to evaluate their effects on the sensitivity calibration results. The results indicate that under the interference of narrowband noise, white noise, and mixed noise, significant errors occur in both the root mean square fluctuation of the sensitivity curve and the peak sensitivity, whereas the error in mean sensitivity is comparatively smaller than that of the aforementioned indicators. These results provide a theoretical foundation for the development of targeted denoising techniques during field verification.

Natural ester insulating oils are increasingly replacing mineral oils as the insulating medium for oil-filled equipment due to their high ignition point, biodegradability, and other environmentally friendly properties. However, the reaction characteristics of natural ester insulating oils under different types of faults require further investigation. This paper presents the development of a molecular dynamics model employing the ReaxFF reactive force field to comprehensively simulate the decomposition of natural ester insulating oils over a temperature range of 2800–4000 K, elucidating the resulting product information. The gas production behaviour of natural ester insulating oils was examined under different overheating conditions and heating times. The simulation results indicate that the thermal decomposition products of natural ester insulating oil primarily consist of seven gases, including H₂, CO, CO₂, and others. Notably, the concentration of C₂H₄ gas exhibits a significantly nonlinear negative correlation with overheating conditions. Because of variations in simulation temperatures, the characteristic gases generated during the thermal decomposition of natural ester insulating oil correspond to different fault types observed in real-world scenarios. Specifically, the gas production at a simulated temperature of 4000 K aligns with the gas production behaviour of insulating oil during discharge fault events in practice. The results of this study offer a theoretical basis for the application of insulation condition monitoring in oil-filled equipment through dissolved gas analysis (DGA).

Silicone rubber (SIR) composite insulators are widely employed in electrical applications due to their exceptional chemical stability, low surface energy and superior electrical insulation properties. To enhance the hydrophobicity and low-temperature resistance of SIR, blended composites with varying ratios of SIR and phenyl silicone rubber (PSIR) were fabricated. The study revealed that matrix-filler network interactions between PSIR and fillers were weaker compared to those in SIR-based systems. Increasing PSIR content led to reduced elongation at break in the composites, while tensile strength remained largely unchanged. Concurrently, the breakdown strength is inferior to that of pure PSIR composites. Notably, the blend of SIR and PSIR enhances both hydrophobicity and resistance to hydrophobicity migration. This work provides a strategic approach for enhancing the performance of SIR composites suitable for applications in regions with high humidity and significant rainfall.