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

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.

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.

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?.

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。

气压湿度对空气隙绝缘特性的影响研究

外界环境条件影响以空气为介质的电力设备外绝缘性能,为了研究空气放电的物理特性,文中基于Boltzmann方程研究空气中电子与分子碰撞的微观过程,计算分析气压、湿度对空气隙绝缘性能的影响规律。结果表明,温度为300 K,气压为1.0 atm(1 atm=101 kPa)时,空气相对湿度的升高会改变电子能量分布函数和电子输运参数。相对湿度每升高30%,电子平均能量下降约0.2 eV,约化电子迁移率下降约0.25×10^(23)(V∙m∙s)^(-1),约化电子扩散系数下降约0.2×10^(24)(m∙s)^(-1),空气相对湿度从0%升高到30%,临界击穿场强升高486 V/cm,空气相对湿度从30%升高到60%,临界击穿场强升高729 V/cm,空气隙绝缘性能增强;温度为300 K,相对湿度为0%时,气压每升高0.2 atm,临界击穿场强升高约6 kV/cm,空气隙绝缘性能增强。

核壳结构BNNS@SiO_(2)/环氧复合电介质的电-热击穿特性

本文制备不同填料含量的核壳结构BNNS@SiO_(2)/环氧复合电介质,研究复合电介质界面区的化学特征与微观形貌,通过热刺激去极化电流法与击穿测试研究环氧复合电介质的陷阱特性与击穿性能。结果表明:BNNS@SiO_(2)具有核壳结构,且包覆的SiO_(2)厚度在纳米级别;BNNS@SiO_(2)表面存在明显化学键合作用,与环氧基体可形成较强的界面区,提升其与环氧基体的相容性。少量BNNS@SiO_(2)可有效提升复合电介质的电气强度,当BNNS@SiO_(2)的质量分数为1%时,复合电介质的电气强度可提升52.3%。当BNNS@SiO_(2)纳米粒子含量较少时,环氧复合电介质中的深陷阱增加,当纳米粒子含量较多时,深陷阱数量有所减少,浅陷阱数量增加。此外,核壳结构BNNS@SiO_(2)/环氧复合电介质的热导率明显提高,有利于高电场下的绝缘散热。通过深陷阱效应与导热性能提升的综合作用,环氧复合电介质的击穿性能得到显著提升。

金属化膜击穿与自愈性能研究

薄膜电容器凭借体积小、储能密度高、安全性好等优点,在直流输电、轨道交通、脉冲功率装置等方面具有重要应用。薄膜电容器常用介质材料包括双向拉伸聚丙烯(BOPP)薄膜和聚对苯二甲酸乙二醇酯(PET)薄膜,本文以两种介质薄膜为研究对象,通过真空蒸镀制备不同方阻的金属化膜,研究了金属层厚度对薄膜击穿强度和自愈性能的影响。两种聚合物的金属化膜都表现为:降低金属层厚度可在一定程度上提高薄膜的击穿强度,由于自愈能量具有统计性,其随电压升高增大,而高方阻薄膜的自愈能量更小,自愈性能更好。实验中也观察到重复自愈现象并对出现的原因做出了解释。

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。

SiO_(2)包覆层对BaTiO_(3)@SiO_(2)复合陶瓷微观结构和储能性能的影响

为了获得高击穿场强和高能量密度的复合陶瓷材料储能电容器,其难点之一是研究应用于复合陶瓷材料的纳米颗粒的界面和边界层的影响。对表面包覆了不同厚度SiO_(2)的不同尺寸的BaTiO_(3)纳米颗粒经烧结得到的BaTiO_(3)@SiO_(2)复合陶瓷材料进行微观表征与储能性能对比研究。研究发现,采用SiO_(2)包覆BaTiO_(3)颗粒烧结的方法提高了陶瓷材料的击穿强度和放电能量密度。减小BaTiO_(3)纳米颗粒的尺寸使BaTiO_(3)与SiO_(2)的界面大量增加,这影响了新相的形成并且使晶体结构发生变化。导致使用较大填料颗粒的BaTiO_(3)@SiO_(2)复合陶瓷材料比使用极细填料颗粒的BaTiO_(3)@SiO_(2)复合陶瓷材料具有更致密的金相组织,更高的击穿场强和更高的放电能量密度。