Development of epoxy resin with superior breakdown strength:A Review

Epoxy resin(EP)has been widely utilized in electrical equipment and electronic devices due to its fascinating electric,thermal,and mechanical properties.However,the complex insulation structures of modern power devices in high-voltage direct current systems pose several challenges for EP-based dielectrics.The most significant among these challenges is the need for EP to stably operate under greater electric fields,requiring superior breakdown strength.This paper summarizes the key factors influencing the breakdown strength of EP and reviews reported methods for enhancing this property.Recognizing the limitations of existing approaches,we propose that the emerging technology of molecule design offers a potentially optimal solution for developing EP with enhanced breakdown strength.Furthermore,we anticipate the future development direction of EP with satisfactory insulation properties.We believe that enhancing the breakdown theory of solid dielectrics,exploring new research and development methodologies,and creating environmentally friendly EP with high performance are primary focus areas.We hope that this paper will offer guidance and support for the future development of EP with superior breakdown strength,proving valuable in advancing EP-based dielectrics.

The effect of polymer type on electric breakdown strength on a nanosecond time scale

Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength （EBD） on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE （polyethylene）, PTFE （polytetrafluoroethelene）, PMMA （organic glass） and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD （PTFE） 〉 EBD （PMMA） 〉 EBD （Nylon） 〉 EBD （PE）. This result is consistent with the theoretical prediction.

Improved Breakdown Strength in(Ba_(0.6)Sr_(0.4))_(0.85)Bi_(0.1)TiO_3 Ceramics with Addition of CaZrO_3 for Energy Storage Application

（Ba（0.6） Sr（0.4））（0.85） Bi（0.1） TiO3 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（Ba（0.6）Sr（0.4））（0.85） Bi（0.1） TiO3 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 k V/mm at x=7.5. In virtue of low dielectric loss（tan d〈0.001 5）, moderate dielectric constant（er 〉1 500） and high breakdown strength（Eb 〉17.5 k V/mm）, the CaZrO3 doped（Ba（0.6）Sr（0.4））0.85 Bi（0.1） TiO3 ceramic is a potential candidate material for high power electric applications.

Mpulse Breakdown Strength of Nano-ZnO/XLPE Nanocomposite Material on Temperature Rise

Development of new materials using composite materials has been much interest. XLPE is a kind of power cable in high voltage insulation. Recently research for cable insulating material has shown that nano-size filler added to XLPE is electrically and physically stable. In this paper, Impulse strength was measured in XLPE that composite by adding na-no-ZnO with different mass proportions. There is positive and negative impulse voltage. However, there is no differ-ence between them on the film specimen. Therefore we tested only positive voltage. In order to understand temperature properties of XLPE nanocomposite sample, experiment of impulse breakdown strength were measured at room temper-ature and maximum allowable temperature (90℃). From this result, it can be considered that the breakdown strength of addition of

Superior energy storage performance of BNT-based ferroelectric ceramics based on maintaining high polarization and breakdown strength

Bi_(0.5)Na_(0.5)TiO_(3)(BNT)-based lead-free ceramics with superior ferroelectric properties are considered to be extremely advantageous in energy storage capacitors for future green technologies.Here,we demonstrate an approach to achieve both ultrahigh energy density W_(rec)and efficiencyηby regulating the multiscale electropolar structures and microstructure.A satisfactory energy storage performance of a high W_(rec)of 4.02 J·cm^(-3),and a decentηof 80%under 415 kV·cm^(-1)are attained in the 0.5(BNT-CS)-0.5SB_(0.2)T ceramic(abbreviated as BNT-0.2SBT).Moreover,BNT-0.2SBT exhibits superior power density(P_(D)=107MW·cm^(-3)),ultrafast discharge time(t_(0.9)=116 ns)at 150 kV·cm^(-1),and good temperature stability.The findings in this work not only demonstrate that a valid candidate,but also provide a new idea of how to achieve both high-energy storage density and efficiency in lead-free ferroelectric materials.

Improved breakdown strength and energy density of polyimide composites by interface engineering between BN and BaTiO3 fibers

Conventionally,interface effects between polymers and fillers are essential for determining the breakdown strength and energy storage density of polymer-based dielectric composites.In this study,we found that interface effects between different fillers have similar behavior.BN and Ba TiO3 fiber composite fillers with three different interface bonding strengths were successfully achieved by controlling composite processes(BT-fiber/BN<BT-fiber@BN<BT-fiber&BN),and introduced into a polyimide(PI)matrix to form composite films.Considerably enhanced breakdown strength and energy storage density were obtained in BT-fiber&BN/PI composites owing to strong interface bonding,compared to other two composite fillers,which are well supported by the data from the finite element simulation.Specifically,PI composites with only 3 wt%BT-fiber&BN possess an optimized energy storage density of approximately 4.25 J/cm^(3)at 4343 k V/cm.These results provide an effective way for adjusting and improving the energy storage properties of polymer-based composites.

Ternary polymer nanocomposites with concurrently enhanced dielectric constant and breakdown strength for high-temperature electrostatic capacitors

The exploration of high-energy-density electrostatic capacitors capable of operating both efficiently and reliably at elevated temperatures is of great significance in order to meet advanced power electronic applications.The energy density of a capacitor is strongly dependent on dielectric constant and breakdown strength of a dielectric material.Here,we demonstrate a class of solution-processable polymer nanocomposites exhibiting a concurrent improvement in dielectric constant and breakdown strength,which typically show a negative correlation in conventional dielectric materials,along with a reduction in dielectric loss.The excellent performance is enabled by the elegant combination of nanostructured barium titanate and boron nitride fillers with complementary functionalities.The ternary polymer nanocomposite with the optimized filler compositions delivers a discharged energy density of 2.92 J cm^−3 and a Weibull breakdown strength of 547 MV m^−1 at 150℃,which are 83%and 25%,respectively,greater than those of the pristine polymer.The conduction behaviors including interfacial barrier and carrier transport process have been investigated to rationalize the energy storage performance of ternary polymer nanocomposite.This contribution provides a new design paradigm for scalable high-temperature polymer film capacitors.

Enhanced breakdown strength of BaTiO_(3)-based multilayer ceramic capacitor by structural optimization

0.5 wt%Nb_(2)O_(5)doped 0.12BiAlO_(3)-0.88BaTiO_(3)(12BA5N)multilayer ceramic capacitor(MLCC-1)was prepared,which satisfied EIA X7R specification(where X is the minimum temperature,R is the percentage of capacitance variation limit)at 1 kHZ.The distribution of internal electric field under breakdown voltage was simulated by finite element method(FEM),indicating that the electric field strength increased significantly at the terminal of internal electrode.These areas may become the headstream of breakdown for MLCC-1 due to the shape mutation.In order to improve the breakdown performance of MLCC-1,it was optimized by 12BA5N+2G green sheets(prepared by 12BA5N ceramic powder with 2 wt%B-Al-Si glass additive),then MLCC-2 was obtained which satisfied EIA X8R specification.Its BDS rose from 20 to29.4 kV·mm^(-1),and the electric field distribution of dielectric layer was also analyzed by FEM.Besides,it was also found that the grain size and the dielectric constants of"core"and"shell"parts for the 12BA5N+2G dielectric layer both contributed to the enhanced BDS of MLCC-2according to the simulation results from FEM.

Prediction of breakdown strength of cellulosic insulating materials using artificial neural networks

In this research work,a few sets of experiments have been performed in high voltage laboratory on various cellulosic insulating materials like diamond-dotted paper,paper phenolic sheets,cotton phenolic sheets,leatheroid,and presspaper,to measure different electrical parameters like breakdown strength,relative permittivity,loss tangent,etc.Considering the dependency of breakdown strength on other physical parameters,different Artificial Neural Network(ANN)models are proposed for the prediction of breakdown strength.The ANN model results are compared with those obtained experimentally and also with the values already predicted from an empirical relation suggested by Swanson and Dall.The reported results indicated that the breakdown strength predicted from the ANN model is in good agreement with the experimental values.

Effects of annealing and firing in wet hydrogen on the dielectric breakdown strengths of alumina ceramics

Annealing and firing in wet hydrogen are widely used steps in the processing alumina.ceramic insulators that may affect their dielectric breakdown strengths(DBS).In this study,the effects of annealing(at 1300℃for 7 h)and firing in wet hydrogen on the DBS of alumina ceramics(all sintered at 1650℃)were studied,and the underlying mechanisms were analyzed by material characterizations.Annealing reduced the DBS of the 95%alumina ceramics due to the inter-granular phase crystallization,and the reduction in the DBS could be correlated to the reduction in mechanical strength.In contrast,annealing improved the DBS of the 99%alumina ceramic without intergranular phase transformation.Firing in wet hydrogen at 1500℃caused the DBS increment,which can be ascribed to the reduction in the concentrations of point defects and electrical carriers.

Simultaneously Improved Dielectric Constant and Breakdown Strength of PVDF-based Composites with Polypyrrole Nanowire Encapsuled Molybdenum Disulfide Nanosheets

High-performance dielectric polymer composites have received increasing attention due to their important applications in the field of energy storage.The rational structural design of hybrid fillers can lead to a balance between high dielectric constant and insulation in composites.In this work,novel hybrid fillers were fabricated by in situ synthesizing one-dimensional polypyrrole nanowires(PPynws)on the twodimensional molybdenum disulfide(MoS_(2)),which integrated the good ion polarization ability of PPynws and the high insulation and adjustable band gap of MoS_(2).Compared with the binary poly(vinylidene fluoride)(PVDF)/MoS_(2) composites,the PVDF/MoS_(2)-PPynws composites exhibited remarkably improved dielectric constant and breakdown strength,while the dielectric loss was still maintained at a low level.An optimal ternary composite with 1 wt%MoS_(2)-PPynws showed a high dielectric constant(15@1kHz),suppressed dielectric loss(0.027@1kHz),and high breakdown strength(422.1 MV/m).PPynws inducing strong interfacial polarization and the highly insulated MoS_(2) nanosheets extending the breakdown path mainly contributed to the synchronously enhanced dielectric constant and breakdown strength.This intriguing synthesis method of PVDF/MoS_(2)-PPynws nanocomposite will open up new opportunities for fabricating nanostructured polymer composites to produce high dielectric materials.

Measurement of Breakdown Electric Field Strength for Vegetation and Hydrocarbon Flames

A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the high-voltage transmission system. In any case, the wildfire plumes provide a conductive path. The electrical conductivity is due to intense heat in combustion zone of the fire which creates ion and electrons from flame inherent particulates. Increase in the ion concentration increases the electrical conductivity of the fire plume. The main purpose of this study was to measure dielectric breakdown electric field for vegetation and hydrocarbon flames. The experimental data is needed for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, hydrocarbon and vegetation fuels were ignited in a cylindrically shaped steel burner which was fitted with type-K thermocouples to measure flame temperature. The fuels consisted of dried weeping wattle (Peltophorum africanum) litter, butane gas and candle wax. Two pinned copper electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. Breakdown electric field strength (Ecrit) obtained from the experiment decreased from 10.5 to 6.9 kV/cm for the flames with temperature range of 1003 to 1410 K, respectively.

Influence of test procedure on dielectric breakdown strength of alumina

Dielectric strength testing of ceramics can be performed with various setups and parameters. Comparisons of results from different sources are often not meaningful, because the results are strongly dependent on the actual testing procedure. The aim of this study is to quantify the influence of voltage ramp rate, electrode size, electrode conditioning, and sample thickness on the measured AC dielectric strength of a commercial alumina. Mean values, Weibull moduli, and failure probabilities determined in standardized short time tests are evaluated and related to withstand voltage tests. Dielectric strength values in the range from 21.6 to 33.2 kV·mm–1 were obtained for the same material using different testing procedures. Short time tests resulted in small standard deviations(< 2 kV·mm–1) and high Weibull moduli around 30, while withstand tests at voltage levels with low and virtual zero failure probability in short time tests resulted in large scatter of withstand time and Weibull moduli < 1. The strong decrease in Weibull moduli is attributed to progressive damage from partial discharge and depolarization during AC testing. These findings emphasize the necessity of a thorough documentation of testing procedure and highlight the importance of withstand voltage tests for a comprehensive material characterization.

SURVEYING INTO THE LIMITING BREAKDOWN STRENGTH AND THE FIGURE OF MERIT OF STRONGLY ELECTRONEGATIVE GASES

The variation of the limiting breakdown strengths of strongly electronegative gases, es-pecially, the gas mixtures, with relative gas concentrations, is discussed. Four basic types ofthe behaviour of the variation have been identified, i.e. the linear relation, the synergisticrelation, the positive synergistic relation and the negative synergistic relation. Here alsodiscussed are the values of the figure of merit of electronegative gases and their mixturesand the relationship of the limiting breakdown strength and the figure of meri?.

Breakdown Properties of Nano-SiO2/LDPE Composite

聚合物纳米复合介质的击穿强度与纳米填充颗粒的质量分数、粒径和表面处理密切相关。以不同表面处理的纳米SiO2颗粒为填料，制备了不同填充质量分数、粒径的纳米SiO2／低密度聚乙烯（low density polyethylene,LDPE）复合介质，测试了其在交流、直流正极性和直流负极性3种不同类型电场下的击穿场强。结果表明：在所研究范围内，填充纳米SiO2颗粒可以提高低密度聚乙烯的击穿场强，并且随着填充质量分数的增加，复合介质的击穿场强有升高的趋势。纳米颗粒填充质量分数相同时，在12～16am粒径下，复合介质的击穿场强有随纳米SiO2粒径的升高而降低的趋势；在7nm小粒径下，可能由于纳米颗粒容易团聚，导致击穿场强较粒径大时要低。另外，纳米SiO2颗粒表面经疏水性处理后，能够有效提高复合介质的击穿场强。

沉析纤维尺寸和含量对间位芳纶纸性能的影响

使用不同目数的筛网对自制的Z沉析纤维进行筛分,将得到的不同尺寸的沉析纤维与间位芳纶短切纤维按一定质量比配抄成纸,制备间位芳纶纸;通过红外光谱、X射线衍射、扫描电镜及热失重、动态滤水分析对自制的Z沉析纤维的化学结构、热性能、动态滤水性能进行表征,并与进口的J沉析纤维对比;研究了沉析纤维的尺寸和含量对间位芳纶纸性能的影响。结果表明:Z沉析纤维与J沉析纤维均为膜状结构,化学结构基本一致,动态滤水性能及热性能相当;经30目或50目的筛网筛分后的沉析纤维可以与短切纤维更好地抱合,间位芳纶纸的抗张强度、断裂伸长率、撕裂度、击穿强度均达到较大值;间位芳纶纸的撕裂度随沉析纤维含量的增加逐渐降低,间位芳纶纸的抗张强度、断裂伸长率、击穿强度随沉析纤维含量的增加呈现先增后降的变化趋势,当沉析纤维质量分数为55%时,间位芳纶纸的抗张强度、断裂伸长率、击穿强度均达到最大值,分别为3.0 kN/m、5.50%、18.7 kV/mm。

微波脉冲大气击穿临界场强估计

针对高功率微波在大气传输中可能出现的击穿现象,研究了脉冲序列中首次击穿时的延迟脉冲数,发现其与种子电子、脉冲击穿概率以及微波场强密切相关。研究发现,微波场强可通过作用于种子电子间接影响脉冲击穿概率和延迟脉冲数,由此提出利用延迟脉冲数估计微波击穿临界场强的方法,并定义在脉冲击穿概率大于一定值时的微波临界场强作为击穿阈值。推导了脉冲击穿概率的估计公式,并对估计量的性能进行了分析,随后利用S波段微波大气击穿模拟装置开展了实验验证。实验结果表明,在一定范围内,重复频率微波脉冲击穿延迟脉冲数仅与种子电子产生率和脉宽成反比,能用于估计脉冲击穿概率,进而给出击穿临界场强。

Enhanced High-Temperature Energy Storage Performance of All-Organic Composite Dielectric via Constructing Fiber-Re in forced Structure

Optimizing the high-temperature energy storage characteristics of energy storage dielectrics is of great significance for the development of pulsed power devices and power control systems.Selecting a polymer with a higher glass transition temperature(T_(g))as the matrix is one of the effective ways to increase the upper limit of the polymer operating temperature.However,current high-T_(g)polymers have limitations,and it is difficult to meet the demand for high-temperature energy storage dielectrics with only one polymer.For example,polyetherimide has high-energy storage efficiency,but low breakdown strength at high temperatures.Polyimide has high corona resistance,but low high-temperature energy storage efficiency.In this work,combining the advantages of two polymer,a novel high-T_(g)polymer fiber-reinforced microstructure is designed.Polyimide is designed as extremely fine fibers distributed in the composite dielectric,which will facilitate the reduction of high-temperature conductivity loss for polyimide.At the same time,due to the high-temperature resistance and corona resistance of polyimide,the high-temperature breakdown strength of the composite dielectric is enhanced.After the polyimide content with the best high-temperature energy storage characteristics is determined,molecular semiconductors(ITIC)are blended into the polyimide fibers to further improve the high-temperature efficiency.Ultimately,excellent high-temperature energy storage properties are obtained.The 0.25 vol%ITIC-polyimide/polyetherimide composite exhibits high-energy density and high discharge efficiency at 150℃(2.9 J cm^(-3),90%)and 180℃(2.16 J cm^(-3),90%).This work provides a scalable design idea for high-performance all-organic high-temperature energy storage dielectrics.

用静电纺丝技术制备纳米片取向结构复合电介质材料

金属化薄膜电容器因其具有超高功率密度而在新能源行业领域受到广泛关注。为了提升薄膜电容器的储能密度,将高绝缘氮化硼纳米片(BNNS)引入到聚偏氟乙烯(PVDF)基聚合物中以制备电容器用高储能复合电介质材料,并利用静电纺丝技术实现BNNS均匀取向的分布。结果表明,均匀取向分布的高绝缘纳米片可以抑制载流子迁移并提升复合材料的击穿场强。结合相场模拟分析可知,均匀取向分布的BNNS结构能调控外电场分布且更有效地阻滞复合材料被击穿,最终在396 MV/m的电场强度下实现高达10.5 J/cm^(3)的储能密度。