Improved Breakdown Strength Research Articles

Electrical tree formation in polymer-filler composites

Insulating fillers are often mixed with polymer dielectrics in order to improve dielectric breakdown strength. However, filler-loaded dielectric films show higher variability, which limits their large-scale utility and application. In this paper, we present a computational framework for predicting the spatial distribution of electrical tree formation in a polymer dielectric in the presence of insulating fillers. The framework is based on the numerical solution of Poisson's equation inside the dielectric film and the application of the Monte Carlo model for finding the electric breakdown path. The simulation results explain several puzzles associated with the breakdown of polymer-filler dielectrics, such as (1) the improved breakdown strength with insulating filler mixing, (2) high degree of variability in breakdown measurements, and (3) effects of filler size, shape and position on the breakdown. In addition, the proposed framework not only provides the physical understanding of the breakdown process but also inspires new design concepts to improve the breakdown strength of the polymer composite.

Significantly improved breakdown strength and energy density of tri-layered polymer nanocomposites with optimized graphene oxide

Advanced electrostatic capacitors with great energy densities are urgently needed for practical applications in high-performance energy storage devices. Herein, poly (methyl methacrylate) (PMMA) is employed as two outer layers to provide excellent insulation characteristic, while ferroelectric copolymer poly (vinylidene fluoride-co-hexafluoropropene) P(VDF-HFP) with dispersed graphene oxide (GO) as the inter layer to enhance dielectric constant (K) and electrical displacement (D). The resulting trilayered nanocomposites exhibit highest electrical displacement difference (Dmax-Drem) value of 7.17 μC cm−2 at a low filler loading of 2 wt% GO under an electrical field of 300 MV m−1. The breakdown strength (Eb) of the designed trilayered nanocomposites are prominently improved at least one order of magnitude in comparison to other configuration films such as single-layered and reversed trilayer structures, as verified by the leakage current measurements and the finite element simulations with 3D models. The trilayered nanocomposites deliver an ultrahigh energy density of 10 J cm−3 and a discharged efficiency of 77% at an applied electrical field of 300 MV m−1, which is among the best energy storage performance under the identical electric field reported so far. The potential applications of the trilayered nanocomposites for energy storage have been further demonstrated by stable performance over a 40,000 charge-discharge cycling.

Physical Mechanism of Breakdown Failure in Polymer Composites with Various Filler Loading

AbstractDielectric polymer materials consisting of zinc sulfide nanoparticles (ZnS_nps) and poly(vinylidene fluoride) (PVDF) were prepared by a solution‐casting process. The introduction of low filler loading results in obviously improved breakdown strength and energy density in comparison with pure PVDF, while the breakdown strength sharply becomes weak in the case of high filler loading. Based on the multi‐core model, the electric double layer theory as well as the physical model we built, we propose that the insulation and charge distribution of the composites are regulated by the inter‐fillers distance between neighboring fillers, resulting in the redistribution of the internal electric filed direction and the increase or decrease of the internal electric filed strength in the applied electric filed.

Novel Nanostructure Composite Dielectric with High Insulation Performance: Silica-Based Nanometer-Sized Porous Composite Insulating Paper Reinforced by Ceramic Fibers

Nano-dielectrics, which were discovered more than 20 years ago, were once considered as promising insulators. Adding or hybridizing inorganic oxides into polymer matrices inevitably results in poor compatibility between multiphase materials and thus results in limited breakdown strength improvement (generally lower than 20%). Therefore, we bypassed the traditional nano-doping method and proposed the direct construction of matrix materials on nanostructures, that is, a ceramic fiber-porous silica composite insulating paper. The breakdown strength of prepared dielectric was remarkably improved by 110%. To the best of our knowledge, such a high improvement in electrical performance has not been reported in previous studies.

Significantly Improved Breakdown Strength and Energy Density in Polymer Composites with High Filler Loading by Constructing Isoelectronic Traps

High-performance dielectric polymer materials consisting of ZnS:O nanoparticles (ZSO NPs) with isoelectronic traps and polyvinylidene fluoride (PVDF) were prepared by a solution-casting method. Com...

Impact of Stabilizer on In Situ Formation of Ag Nanoparticles in Polyvinylidene Fluoride (PVDF) Matrix

In situ synthesis of Ag nanoparticles in polyvinylidene fluoride (PVDF) was investigated using different stabilizers such as 3-aminopropyltrimethoxysilane (APS) and 1-dodecanethiol (thiol). Although PVDF is a matrix, it also functions as a stabilizer. Results of UV-vis spectroscopy showed that when APS or PVDF was used, Ag nanoparticles were formed. Yet no formation occurred when thiol was used due to the complexation of Ag+ ions by thiol. Polar groups on stabilizers has an important effect on complexation process. APS, a nitrogen-based ligand, has hard base character inhibiting the complexation between Ag+ and APS. Consequently, Ag+ ions are reduced to Ag nanoparticles in N,N dimethyl formamide (DMF), which acts as a solvent and reducing agent. Transition Electron Microscopy (TEM) image showed a uniform distribution of spherical Ag nanoparticles in PVDF matrix in the presence of APS. The electrical properties of flexible nano-metal polymer were tested and the highest improvements in breakdown strength and energy density of 33 and 58 %, respectively were measured with 0.05 wt.% Ag content and APS as a stabilizer.

Phase structure and energy storage performance for BiFeO3–BaTiO3 based lead-free ferroelectric ceramics

Abstract Recently, BiFeO3–BaTiO3 (BF-BT) lead-free ferroelectric ceramics have been widely concerned and deemed as one of the most promising candidates for lead-free energy-storage material because of their high spontaneous polarization and excellent energy storage properties. Herein, a series of Bi1-zLazFeO3-xBaTiO3+yMnO2 (BLzF-xBT-yMn at 0.45 ≤ x ≤ 0.60 mol, 0.0 ≤ y ≤ 0.4% mol and z = 0 or 0.02 mol) ceramics were prepared to reveal their energy-storage performance. With increasing x, the breakdown strength (BDS) increases, while the maximum polarization (Pmax), remanent polarization (Pr), and the difference value between Pmax and Pr (ΔP) decrease. Because of the high BDS and ΔP, a large energy storage density Wre = 1.08 J/cm3 is achieved in BF-0.48BT ceramics as the electric field is 130 kV/cm. In addition, with increasing y and z, the increasing BDS and ΔP have been observed. Due to the improvement in BDS and ΔP, an excellent Wre = 1.22 J/cm3 was achieved in Bi1-zLazFeO3-xBaTiO3+yMnO2 ceramics at x = 0.48, y = 0.3% and z = 0.02. This work provides the clue for application of the high-power-energy BF-BT ceramics.

Fabrication of PMIA/fBN Dielectric Composite with Enhanced Breakdown Strength and Thermal Conductivity

A high-temperature poly (m-phenyleneisophthalamide) (PMIA) dielectric composite was successfully manufactured with functionalized BN (fBN) fillers. Due to effective modification by KH-550, fBN particles evenly dispersed in PMIA matrix. The dielectric property, breakdown strength and thermal conductivity of PMIA/fBN dielectric composite were researched. The consequences indicate that fBN fillers can not only decrease the dielectric loss but also enhance the breakdown strength of PMIA/fBN dielectric composites. Furthermore, owing to the generated heat transfer pathways by fBN particles, the thermal conductivities improved from 0.23 W·m-1·K-1 of fBN-0 to 0.86 W·m-1·K-1 of fBN-30, demonstrating a significant improvement. These results present a novel method for fabricating high-temperature PMIA/fBN dielectric composites with improved breakdown strength and thermal conductivity.

Preparation Methods of Polypropylene/Nano-Silica/Styrene-Ethylene-Butylene-Styrene Composite and Its Effect on Electrical Properties.

Compared with traditional insulation materials, such as cross-linked polyethylene (XLPE), polypropylene (PP) is famous for its better recyclable and thermal properties, as well as its good electrical performance. However, the problem of poor impact strength has restricted the application of pure PP in high-voltage, direct current (HVDC) cables. In this paper, styrene-ethylene-butylene-styrene block copolymer (SEBS) was used as a toughening filler, and nano-SiO2 was expected to improve the electric properties of the nano-composite. By controlling the masterbatch system, the dispersion characteristics of nano-SiO2 in the ternary composite system were changed. When PP/SiO2 was used as the masterbatch and then blended with SEBS, nano-SiO2 tended to disperse in the PP phase, and the number of nano-particles in the SEBS phase was lower. When PP/SEBS was used as the masterbatch, nano-SiO2 was distributed in both the PP phase and the SEBS phase. When SEBS/SiO2 was used as the masterbatch, nano-SiO2 tended to be dispersed in the SEBS phase. The different dispersion characteristics of nano-SiO2 changed the crystallization and mechanical properties of the ternary composite system and produced different electrical performance improvement effects. The results of our experiment revealed that the space charge suppression capability was positively correlated with the direct current (DC) breakdown strength improvement effect. Compared with the DC performance of 500 kV commercial XLPE materials, the self-made PP-based ternary composite system has better space charge suppression effects and higher DC breakdown strength. When nano-SiO2 was more dispersed in the PP phase, the space charge improvement effect was best. When the nano-SiO2 particles were more dispersed in the SEBS phase, the expected electrical property improvement was not obtained. Scanning electron microscopy showed that the nano-SiO2 particles in the SEBS phase were more dispersed at the interface than in the SEBS matrix, indicating that the nano-particles were poorly dispersed, which may be a reason why the electrical properties of the composite system were not significantly improved.

Research on Creeping Flashover Characteristics of Nanofluid-Impregnated Pressboard Modified Based on Fe₃O₄ Nanoparticles under Lightning Impulse Voltages.

Creeping flashover of mineral-oil-impregnated pressboard under impulse stress is a common insulating failure in oil-immersed transformers, arousing increasing attention. Recent studies have shown that the breakdown strength of transformer oil under positive lightning impulse voltage can be significantly improved through nanoparticles-based modification, and Fe3O4 has shown the best improvement in breakdown strength compared to other nanoparticles that have been used. This paper presents the creeping flashover characteristics of pure oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) based on Fe3O4 nanoparticles under positive and negative lightning impulse voltages, respectively. It was found that NIP possessed higher resistance to creeping flashover than OIP. The relative permittivities of oil and oil-impregnated pressboard before and after nanoparticles-based modification were measured, and the results revealed that the addition of nanoparticles led to a better match in relative permittivity between oil and oil-impregnated pressboard, and a more uniform electric field distribution. Furthermore, the shallow trap density in NIP was obviously increased compared to that of OIP through the thermally stimulated depolarization current (TSDC), which promoted the dissipation of surface charges and weakened the distortion of the electric field. Therefore, the creeping flashover characteristics of oil-impregnated pressboard were greatly improved with Fe3O4 nanoparticles.

Enhancement of breakdown strength of multilayer polymer film through electric field redistribution and defect modification

Multilayer structural design (including sandwich structure) has received wide attention due to its complementary advantages of different layers in the field of high energy density dielectric materials. Although multilayer polymer composites with improved breakdown strength and energy density have been prepared in some studies, the key mechanism is not clear. In this work, different kinds of multilayer films consisting of various pure polymer [polyimide, poly(vinylidene fluoride) (PVDF), and polypropylene (PP)] layers were prepared to investigate the underlying mechanism of improved performances by multilayer structural design. Experimental results indicated that the relative position of the multilayer film and electrode had an effect on the result of breakdown strength. Meanwhile, when the layer with high relative permittivity (high-k layer) came in contact with the negative electrode, the thinner the high-k layer was, the more remarkable the enhancement of the multilayer materials breakdown strength was. Finally, a double-layer film of PP and PVDF with a Weibull breakdown strength of 649.31 MV/m, which was 60.83 MV/m higher than that of the commercial PP film, was prepared. The simulation result showed that the coating high-k layer could effectively restrain the local electric field distortion around the defect. This study reveals an effective way to improve the breakdown strength of films, which is of great significance for the improvement of capacitor performance and enhancement of energy storage.

Constructing layered structures to enhance the breakdown strength and energy density of Na0.5Bi0.5TiO3-based lead-free dielectric ceramics

The improvement of breakdown strength for NBT-based ceramics is currently the main challenge in applications of lead-free dielectric energy-storage materials.

Improved Energy Storage Performance of Linear Dielectric Polymer Nanodielectrics with Polydopamine coated BN Nanosheets.

Polymer-based nanodielectrics have been intensively investigated for their potential application as energy storage capacitors. However, their relatively low energy density (Ue) and discharging efficiency (η) may greatly limit their practical usage. In present work, high insulating two-dimensional boron nitride nanosheets (BNNS), were introduced into a linear dielectric polymer (P(VDF-TrFE-CTFE)-g-PMMA) matrix to enhance the energy storage performance of the composite. Thanks to the surface coating of polydopamine (PDA) on BN nanosheets, the composite filled with 6 wt% coated BNNS (mBNNS) exhibits significantly improved breakdown strength (Eb) of 540 MV/m and an energy density (Ue) of 11 J/cm3, which are increased by 23% and 100%, respectively as compared with the composite filled with the same content of pristine BNNS. Meanwhile, η of both composites is well retained at around 70% even under a high voltage of 400 MV/m, which is superior to most of the reported composites. This work suggests that complexing polymer matrix with linear dielectric properties with surface coated BNNS fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency.

Improved breakdown strength and energy density of Al2O3/nano-ZrO2 composite films via enhanced interfacial repairing behavior

Taking Al as top electrode, a repairing layer with ultrahigh dielectric strength and resistivity was generated at the interface between sol-gel Al2O3 films and electrodes under the applied electric field. This repairing layer effectively restored the defects on the film surface and improved the dielectric strength. More importantly, it was found that adding ZrO2 nanoparticle into the matrix film could further enhance the dielectric strength, since the ZrO2 nanoparticle is conductive to forming the interfacial repairing layer. The analysis of ac conduction properties showed that the introduction of nano-ZrO2 resulted in a lower potential barrier and a longer hopping distance for ionic migration. In addition, the simulation result indicated that nano-ZrO2 addition induced a local region of high electric field that accelerated ionic migration. As a result of the two factors, the nanocomposite structure of Al2O3/nano-ZrO2 is capable to provide more ions for the formation of interfacial repairing layer. With the stronger repairing behavior, Al2O3/nano-ZrO2 composite films exhibited significantly enhanced breakdown strength of ~ 576 MV/m and energy density of 14.7 J/cm3, in contrast with 385 MV/m and 5.9 J/cm3 for pure Al2O3 films with Al electrodes.

Effects of additives on dielectric strength of naphthenic transformer oil

In order to investigate the effects of additives on electrical breakdown strength of naphthenic transformer oil, three types of additives including N, N′-dimethyl aniline (DMA), trichloroethylene (TCE) and TiO2 nanoparticles were used to modify the oil with different concentrations. The breakdown strength and prebreakdown streamer propagation process in the pure and modified oils were investigated under positive lightning impulse voltage. The test results indicate that all additives can improve the breakdown strength of naphthenic transformer oil at certain concentrations, and TiO2 nanoparticles exhibit an optimal modification effect with an increase of 39.4%. Moreover, streamer propagation characteristics of modified oils are significantly affected by the type of additives. The presence of DMA increases the number of discharge branches, while TCE shortens the propagation length of branches without any obvious change in the shape. The positive streamers in the oil modified by TiO2 nanoparticles possess both denser branches and much slower velocities. Based on the analysis of molecule ionization and distribution characteristics of space charge, the improvement in breakdown strength and the change of prebreakdown process are mainly attributed to the significant influence of additives on the formation and transportation of charge carriers in the naphthenic transformer oil.

High breakdown strength and outstanding piezoelectric performance in flexible PVDF based percolative nanocomposites through the synergistic effect of topological-structure and composition modulations

Over decades, the fabrication of flexible poly(vinylidene fluoride) (PVDF) based percolative nanocomposites with high piezoelectric performance is of great concern from both academia and industry. However, the issue of sharply declined breakdown strength in percolative nanocomposites poses an obstacle to realizing the full potential of conductive nanofillers in enhancing piezoelectricity. Herein, we demonstrated that through proper topological structure and composition modulations, notably improved breakdown strength and piezoelectric performance can be achieved in PVDF based percolative nanocomposites. By constructing a sandwiched structure where a layer of high breakdown strength is intercalated between layers containing high content (near percolation threshold) of conductive nanofillers, the breakdown strength of overall nanocomposites is significantly strengthened and thus allows for sufficient poling of outer layers, fulfilling the great potential of conductive nanofillers in yielding piezoelectricity enhancement. A super high piezoelectric coefficient d33 of 48 pC/N is obtained in the optimized sandwich nanocomposites.

Improved Breakdown Strength in (Ba0.6Sr0.4)0.85Bi0.1TiO3 Ceramics with Addition of CaZrO3 for Energy Storage Application

(Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramics doped with x wt%CaZrO3 (x= 0-10) were synthesized by solid-state reaction method. The effects of CaZrO3 amount on the dielectric properties and structure of (Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramics were investigated. X-ray diffraction results indicated a pure cubic perovskite structure for all samples and that the lattice parameter increased till x=5 and then slightly decreased. A homogenous microstructure was observed with the addition of CaZrO3. Dielectric measurements revealed a relaxor-like characteristic for all samples and that the diffusivity γ reached the maximum value of 1.78 at x=5. With the addition of CaZrO3, the dielectric constant dependence on electric field was weakened, insulation resistivity enhanced and dielectric breakdown strength improved obviously and reached 19.9 kV/mm at x=7.5. In virtue of low dielectric loss (tan δ 1 500) and high breakdown strength (Eb >17.5 kV/mm), the CaZrO3 doped (Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramic is a potential candidate material for high power electric applications.

Alignment of Boron Nitride Nanofibers in Epoxy Composite Films for Thermal Conductivity and Dielectric Breakdown Strength Improvement.

Development of polymer-based composites with simultaneously high thermal conductivity and breakdown strength has attracted considerable attention owing to their important applications in both electronic and electric industries. In this work, boron nitride (BN) nanofibers (BNNF) are successfully prepared as fillers, which are used for epoxy composites. In addition, the BNNF in epoxy composites are aligned by using a film casting method. The composites show enhanced thermal conductivity and dielectric breakdown strength. For instance, after doping with BNNF of 2 wt%, the thermal conductivity of composites increased by 36.4% in comparison with that of the epoxy matrix. Meanwhile, the breakdown strength of the composite with 1 wt% BNNF is 122.9 kV/mm, which increased by 6.8% more than that of neat epoxy (115.1 kV/mm). Moreover, the composites have maintained a low dielectric constant and alternating current conductivity among the range of full frequency, and show a higher thermal decomposition temperature and glass-transition temperature. The composites with aligning BNNF have wide application prospects in electronic packaging material and printed circuit boards.

Highly dispersive Ba 0.6 Sr 0.4 TiO 3 nanoparticles modified P(VDF‐HFP)/PMMA composite films with improved energy storage density and efficiency

Polymer composite films with high energy density as well as high efficiency are promising dielectric materials in pulsed power systems. In improving the energy discharged efficiency, poly vinylidene fluoride-hexafluoropropylene [P(VDF-HFP)] film blended with 20 vol.% poly(methylmethacrylate) (PMMA), which has a much slimmer ferroelectric hysteresis loop, is employed as the polymer matrix. Highly dispersive Ba0.6 Sr0.4 TiO3 (BST) nanoparticles with an average particle size of 12.1 nm are utilised to improve the polarisation of the blend film without sacrificing the dielectric strength. Uniform nanocomposite films with high flexibility and excellent energy-storage performance are obtained. Especially, due to the optimisation of both polymer matrix and fillers, the BST modified P(VDF-HFP)/PMMA blend films show improved breakdown strength and depressed energy loss, which leads to an enhanced energy density of 10.3 J/cm3 at 378 kV/mm.

High energy density induced by DA@NBT powders in PVDF flexible and transparent composite films

Energy storage of polymer-ceramic composite films is urgently demanded in modern electric power supply and renewable energy system. Herein, a series of flexible composite films are fabricated by combining Na0.5Bi0.5TiO3@dopamine (NBT@DA) as filler and poly(vinylidene fluoride) (PVDF) as matrix via a solution casting method. The sample with 1 vol% NBT@DA/PVDF composite film exhibits the highest breakdown strength (380 kV/mm), and thus a high energy density of 9.16 J/cm3 is achieved in the composition, which is 1.5 times higher than that of pure PVDF. The improved breakdown strength is attributed to the reduced mobility of polymer chains induced by the NBT@DA powders. In addition, the outstanding transmittance and flexibility make the composite films as a promising candidate for future flexible portable energy devices.