IET Nanodielectrics最新文献

Epoxy resin-based dielectric materials are widely used for electrical insulation. However, due to the application of electrical equipment in complex and diverse climatic environments, the characteristic variation of the material must be paid attention to. Besides, decoupling of the overall performance is necessary to trace the source of property variation. Thus, in this research, the polarisation characteristics over broad ranges of temperature and frequency of typical epoxy resin used for electrical insulation are investigated. Moreover, the Dissado–Hill model is adopted to quantitatively decouple the individual contribution of each microprocess. It indicates that the magnitudes of the polarisation processes below the glass transition temperature (T_g) are small, the influence of which on the overall polarisation characteristics is marginal. In comparison, the influence of α relaxation initiating above T_g on the magnitude of permittivity and the dielectric loss is prominent, which must be fully taken into consideration during insulation design. In addition, due to the long structure of repeating units in the backbone of epoxy, another polarisation process would appear at higher temperatures stemming from the internal relaxation of repeating units. Furthermore, the amplitude of conductance increases exponentially as temperature rises and would become the major component of loss at elevated temperatures. This research provides insights into the rational design of insulation structures and the development of novel epoxy materials.

During the operation of HVDC transmission systems, the oil-pressboard insulation of converter transformers is constantly subjected to combined AC and DC voltages. The DC voltage component can easily lead to charge accumulation and induce surface flashover. To investigate the development process of surface flashover in oil–pressboard insulation under DC voltage and its influencing factors, this paper establishes a two-dimensional simulation model using finite element simulation software to study the electric field and charge distribution characteristics of oil–pressboard composite insulation systems. Using the established model, the paper analyses the influence of voltage, gap distance and electron mobility on the surface flashover development process.

HFO-1336mzz(E)/CO₂, an eco-friendly insulating gas, garnered considerable interest recently as a potential substitute for SF₆ in gas-insulated equipment. To reduce the precipitation of fluorocarbon gases and solids during the decomposition process of HFO-1336mzz(E)/CO₂ gas mixture, O₂ is normally introduced as an additive. Herein, we investigated the influence of oxygen on the insulation performance of HFO-1336mzz(E)/CO₂ under different electric field non-uniformities by evaluating the breakdown voltage, PDIV, PDEV and decomposition characteristics. The findings indicate that in a quasi-uniform electric field, the breakdown voltage of the gas mixture progressively increases with the oxygen volume fraction. Under the extremely non-uniform electric field, both the breakdown voltage and PDIV initially rise and subsequently decline with the increase of oxygen volume fraction, reaching a peak at 6%. The PD decomposition analysis reveals that the addition of 4% oxygen can reduce the decomposition of HFO-1336mzz(E), which is most beneficial to improve the comprehensive insulation performance of the gas mixture.

Biaxially oriented polypropylene (BOPP), the dielectric material of choice for polymer film capacitors, is widely used in advanced electronic devices and power grids, among other applications. However, the nonlinear growth of the conduction loss at high temperatures leads to a rapid deterioration of its energy storage performance, which seriously hinders the development trend of miniaturisation and high integration of power systems. In this study, inorganic nanolayers with heterogeneous structure were grown on the surface of BOPP films by magnetron sputtering using high dielectric constant BaZrTiO₃ and wide bandgap Al₂O₃ ceramic targets. Experimental and theoretical analyses show that the use of wide bandgap Al₂O₃ as the heterojunction outer layer can effectively impede carrier injection and transport, leading to a significant reduction in the leakage current density of the composite film, effectively enhancing the high temperature energy storage performance of the composite films. The synergistic enhancement of the inorganic heterojunction structure on the dielectric properties and insulating strength of the polymer film is attributed to the ability of the Al₂O₃/BaZrTiO₃/BOPP/BaZrTiO₃/Al₂O₃ (O-B-P-B-O) composite films to exhibit a discharge energy density of 2.49 J/cm³ and a charge/discharge efficiency of 77.6% at 125°C and 500 MV/m.

Polypropylene plays an irreplaceable role in electrical insulation and electrostatic capacitors and has been extensively studied with its microstructure and insulation properties optimised for high-power density miniaturised devices. The extrinsic modifiers or industrial upgrading have not yet achieved a remarkable breakthrough in either concise theory or comprehensive performance. Here, we develop a nonisothermal shear process on melt to regulate the nucleation density and the lamellar orientation along the surface and reveal pore defects in disorder boundaries between spherulites as the microscopic nature of the property bottleneck. The high-rated shear process induces a crystallographic surface texture of (1 1 0) planes from which the elimination of micro-defect benefits. Our high-rated shear strategy achieves an excellent dielectric strength of 573.7 MV/m with an increase of 33% and an improved insulation resistance by 130% at 100 MV/m with the minimised absorption of injected current.

Early detection of brain tumours is crucial for timely treatment, improving survival rates, and preventing severe neurological complications. When successful procedures for early identification are applied to brain tumours, it might preserve people. The article illustrates an original biological device for finding the first signs of brain tumour cells based on photonic crystal fibre (PCF) equipment performing within the terahertz (THz) band. The suggested scanner is a helpful instrument in tumour tissue diagnosis due to its extremely sensitive nature along with minimal transmission degradation. The photonic crystal fibre's distinctive arrangement, utilised by the terahertz frequency spectrum, permits accurate classification of healthy and tumour parts according to the differences in electromagnetic features. Typical tissue in the brain contain damage, tumours, as well as cells that are cancerous. When juxtaposed with previous PCF-based biological indicators, the device that is recommended has excellent comparative response with minimal expenses. The sensing device has a relative sensitivity of 99.26%, an effective area of 4.77 × 10⁻⁸ m², a minimal confinement loss of 9.55 × 10⁻⁶ cm⁻¹, and a low effective material loss of 0.00219 cm⁻¹. The findings of this investigation indicate a big step forward for biological observing equipment, providing a hopeful approach to prompt identification of brain tumours for possible commercial diagnostic possibilities.

Perfluoropentanone (C₅F₁₀O) gas mixtures are expected to be used in gas-insulated switchgear due to their excellent environmental and insulating properties. Nevertheless, the study of the insulating properties and influencing factors of C₅F₁₀O gas mixtures under the internal conditions of gas-insulated switchgear is not yet comprehensive. This paper comprehensively investigates the insulating properties of C₅F₁₀O/dry air gas mixtures. The findings demonstrate that adding C₅F₁₀O significantly enhances the insulating properties of the gas mixture. The findings of this research serve as a valuable reference for the engineering application, operation, and maintenance of C₅F₁₀O/dry air gas mixtures.

The rapid advancement of new energy vehicles has exposed critical limitations in conventional enamelled wire insulation materials for drive motors, particularly in meeting escalating operational demands. Polyimide is widely adopted in the motor insulation systems, and its inherent corona resistance remains insufficient under extreme conditions. Herein, we propose a strategy to improve the corona resistance of PI films or PI polymer based on the integration of silicon dioxide (SiO₂) and aluminium nitride (AlN) nanoparticles. The results indicate that the excellent insulation of SiO₂ and the high thermal conductivity of AlN can lead to a strong effect in improving the corona resistance life of PI. The resultant polymer film (MPI/ASA3) exhibits an excellent corona resistance life of 184.7 min which is 23.38 times higher than that of the MPI/1.0 vol% AOC film. Meanwhile, it still maintains excellent thermal and mechanical properties. Hopefully, our work could promote the advancement of the drive motor for new energy vehicle technology.

Polyimides with combined high thermal resistance and excellent electrical properties are specifically desired for various electrical and power electronic systems. However, traditional polyimide lacks functional groups with huge dipole moments and hence suffer from intrinsic inferior permittivity. Dipolar polymers, as potential high permittivity materials, have received considerable attention. Here, rigid and twisted fluorene groups are introduced into the polyimide backbone, containing urea groups in the side chain. The twisted fluorene structure provides free volume for dipole rotation, which can effectively improve the dipole mobility and avoid the problem of elevated dielectric loss caused by the dipole-flip lag, whereas the urea groups with high dipole moments contribute to the elevation of the permittivity. Ultimately, a clever balance between high permittivity and low dielectric loss is realised through the molecular structure design; BP-BU_0.7 exhibits a high permittivity of 6.37 and a low dielectric loss of 0.0083 at room temperature and 1 kHz. Simultaneously, taking advantage of this characteristic, BP-BU_0.7 is used as the gate dielectric for the organic thin-film transistor (OTFT), and the device exhibits outstanding field-effect properties with low threshold voltage (−0.96 V) and high carrier mobility (4.09 cm² V⁻¹ s⁻¹) under low voltage (−5 V) operation. This polyimide material is considered as a potential dipole glass polymer dielectric for electronic applications.

Winding deformations and insulation dampness are the two main causes for the creeping flashover along the dielectric surfaces of oil-immersed power transformers, which could lead to main insulation failures and explosions. In this paper, these two types of insulation defects are modelled by evaluating creeping discharge tests due to moisture dripping and local electric field enhancement in a transformer protype. The completed creeping process along the dielectric interface, from partial discharge initiation to eventual flashover, was observed using an SLR camera and electro-optical coupled sensors. The results indicate that the evolution of the two types of discharges can be divided into four stages, that is, initial weak discharge at the tip of the high voltage side, appearance of carbonised traces at the tip, strong arc discharge in the gap between the high and low voltage sides and eventual flashover. Creeping discharges caused by insulation dampness grow faster than that caused by winding deformations, in terms of discharge intensity and carbonised pressboard areas. Therefore, the more serious surface discharge phenomenon under the condition of insulation and humidity in this paper is mainly caused by the more obvious space charge accumulation brought by low-density areas such as bubbles.