高频电压下交联聚乙烯电缆绝缘中电树枝生长的动力学模型

针对高压交联聚乙烯电缆绝缘试样,在1000—2000Hz 10kV峰值正弦电压下,采用计算机实时显微数字摄像技术进行了电树枝培养实验.基于半结晶绝缘材料中电树枝生长机理和电树枝结构的分形特征,提出了一个在高频范围定量预测电应力驱动下交联聚乙烯电缆绝缘中电树枝生长特性的动力学模型,获得了电树枝生长率方程和从电树枝生长到击穿过程的寿命公式.将该模型预测值与实验中获得的电树枝生长规律实验数据进行比较,其结果有较好的一致性,表明提出的模型化方法可以应用到交联聚乙烯电缆绝缘中电树枝老化规律的定量分析研究中. 关键词： 交联聚乙烯电缆绝缘 电树枝 施压频率 动力学模型     

Structure characteristics of electrical treeing in XLPE insulation under high frequencies

Electrical tree structure is one of the most important influencing factors for electrical treeing characteristics in polymers. In this paper, we focused on the structure characteristics of electrical treeing in cross-linked polyethylene (XLPE) insulation under high-frequency voltages. The tree structure characteristics include structure distribution characteristics and structure conversion characteristics. The influences of voltage, frequency, and pin-plane spacing on tree structure characteristics were analyzed based on the experimental results. It can be concluded that tree structures regularly change with the local electric field and frequency. The electric field in a very small zone near the needle tip is an important influencing factor for the formation of bush-like trees, and the lowest frequencies for the observed pure-vine-like trees increased with voltage. For double-structure trees, the local electric field at the transition location of the two structures remained almost unchanged with voltage and pin-plane spacing, but obviously increased with frequency. In order to investigate the relations of the growth rate and fractal dimension with tree structure characteristics, a new parameter, the energy threshold W_t, has been introduced and calculated for different tree structures.     

发展在XLPE电缆绝缘内外侧的电树枝

以XLPE高压电力电缆内外侧绝缘中的电树枝特性为研究对象，通过分析电树枝引发与生长的统计实验规律和采用扫描电子显微镜分析发现，由于不同结晶状态的影响，电缆绝缘内外侧的电树枝特性存在很大的差异.引发于绝缘内侧电树枝引发时间短、生长速度快、电树枝形状具有多样性；起始于绝缘外侧的电树枝不仅引发时间长、生长速度极慢，而且电树枝形状(结构)比较单一.并对这两个位置电树枝的引发和生长机理进行了探讨. 关键词： 电树枝 结晶状态 统计规律 内侧和外侧绝缘层     

交联聚乙烯电缆绝缘材料中电树枝的导电特性研究

利用光学显微观察、局部放电测量和共聚焦Raman光谱分析相结合的方法, 研究了交联聚乙烯(XLPE)电缆绝缘材料中两种典型电树枝的导电特性.尽管具有相似的培养条件, 两种电树枝却呈现出完全不同的形态,其中9 kV下典型电树枝为枝-松枝状, 11 kV下为枝状, 而且电树枝生长及局部放电规律呈现出明显的差异.枝-松枝状电树枝主干通道内存在无序石墨碳的沉积, 根据石墨碳G带与D带的相对强度,估算碳层厚度约为8 nm,树枝通道单位长度电阻小于 10 Ω· μm^-1,足以抑制电树枝内局部放电的发展,电树枝呈现出导电型电树枝特征. 枝状电树枝通道内观察到荧光背景,存在材料劣化的产物,但不存在无序石墨碳的聚集, 通道具有明显的非导电特性而不足以抑制电树枝内局部放电的连续作用. 最后提出了XLPE电缆绝缘材料中导电型和非导电型电树枝的单通道生长模型, 利用等效电路理论对XLPE电缆绝缘材料中两种不同导电特性电树枝的生长机理进行了探讨.     

冷绝缘超导电缆绝缘设计及测试方法的简介

超导电缆主绝缘的设计在整个超导电缆的设计中占有十分重要的地位。文中介绍了冷绝缘HTS电缆主绝缘的设计方法和绝缘性能的检测方法;对于超导电缆耐受电压、设计场强和绝缘厚度的确定以及超导电缆主绝缘的性能检测都做了详细的总结;同时也介绍了由于失超引起的局放对绝缘设计的影响。该文所介绍的设计方法和性能检测方法能够为超导电缆主绝缘的设计和绝缘性能检测提供一些参考。     

10 kV交联聚乙烯电缆中超声波传播规律

电缆局放会产生超声波,利用超声波可以进行局放定位和大小估计.为了研究电缆中局放超声波的传播规律,利用COMSOL建立了基于10 kV交联聚乙烯电力电缆本体的声压场仿真模型,探究了超声波在电缆中的扩散过程和电缆表面超声波峰峰值随传播距离的变化规律之间的关系,并在真实10 kV单相交联聚乙烯电缆上进行了超声波衰减实验,探究了真实电缆表面超声波峰峰值随传播距离的衰减规律.结果表明:电缆表面声波峰峰值随传播距离的衰减符合指数规律,衰减系数α=0.07 Np/mm(或0.62 dB/mm),并且是电缆内部声波的扩散过程导致了电缆表面声波峰峰值的严重衰减.据此,针对10 kV交联聚乙烯电缆,建议将局放超声传感器安装在距离局放易发位置100 mm以内,还提出了判断电缆中局放超声波扩散过程结束位置的方法,为确定其他类似型号电缆安装超声传感器的位置提供参考.     

Structural and ac electrical properties of a newly synthesized single phase rare earth double perovskite oxide: Ba2CeNbO6

A single phase rare earth double perovskite oxide Ba₂CeNbO₆ (BCN) is synthesized by solid-state reaction technique for the first time. The X-ray diffraction pattern of the sample at room temperature shows monoclinic structure, with the lattice parameters, a=5.9763 Å, b=5.975 Å and c=8.48 Å and β=90.04°. Impedance spectroscopy is used to study the ac electrical behavior of this material as a function of frequency (10²-10⁶ Hz) at various temperatures (30-450 °C). A relaxation is observed in the entire temperature range. Conduction mechanism is investigated by fitting the complex impedance data to Cole-Cole equation. Complex impedance plane plots show only one semicircular arc, indicating only the grain contribution of dielectric relaxation. The scaling behavior of imaginary part of electric modulus (M″) and imaginary part of electrical impedance (Z″) suggests that the relaxation describes the same mechanism at various temperatures. The frequency dependence of conductivity is interpreted in terms of the jump relaxation model and is fitted to Jonscher's power law. The values of dc conductivities extracted from the Jonscher power law varies from 2.79×10⁻⁷ to 3.5×10⁻⁵ Sm⁻¹ with the increase in temperature from 100 to 450 °C. The activation energies (0.37 eV) extracted from M″(ω) and Z″(ω) peaks are found to follow the Arrhenius law.     

聚丙烯中电树枝生长机理研究

耐电树枝老化特性是表征聚合物绝缘材料介电性能的重要参数之一.聚丙烯(PP)是典型半结晶聚合物,其复杂的非均匀聚集态结构影响电树枝的生长.本文对PP及加入成核剂的PP试样进行了耐电树枝化性能实验,通过偏光显微镜(PLM)及差示扫描量热法(DSC)分析加入成核剂前后PP的结晶形态、结晶度以及结晶结构对电树枝生长特征的影响.以相界面自由能的热驱动作用以及放电雪崩理论为基础,对电树枝生长的热力学和动力学机理进行分析,阐明电场分布对电树枝生长的重要作用.根据半结晶材料的结晶相和非晶相的物理性能,建立材料内部电场分布计算模型,模拟针-板电极条件下聚合物材料内部的局域电场分布情况,分析了电树枝通道的动力学生长特征,探讨了成核剂改变PP的结晶结构抑制电树枝沿电场生长的作用.     

改进RCF算法的电缆绝缘层边缘检测

目前电缆绝缘层厚度检测算法主要采用图像处理技术提取出绝缘层的边缘轮廓,此类算法存在绝缘层边缘过宽和边缘不连续等问题,影响了后续的检测精度.为提高绝缘层测量精度,新算法基于RCF算法进行改进,在模型的4、5阶段采用空洞卷积,增大模型的感受野;并在侧输出网络加入尺度增强模块(SEM模块)和由浅到深的级联网络,增加侧输出图像...     

高温超导电缆直流测试电源平台的搭建

根据高温超导电缆测试用直流电源平台的要求,建立了硬件平台。该平台为模块化结构,具有输出精度高,便于扩展等特点;为方便操作,建立了基于LabVIEW的软件平台,对直流电源平台进行远程控制,并给出了远程控制的程序流程图,实现了电流的匀速上升和下降以及上升过程中的中断操作;利用该电源平台进行了超导电缆的临界电流测试实验,验证了直流电源平台符合高温超导电缆的测试要求。     

Li-doping effects on the electrical properties of ZnO films prepared by the chemical-bath deposition method

Zn_1−xLi_xO thin films, with x varying from 0.0 to 0.5, successfully have been deposited on glass substrates using the chemical bath deposition (CBD) technique. J–E characteristics, DC conductivity and dielectric measurements have been carried out. These measurements were done as a function of temperature, Li concentration and applied electric field intensity. The J–E characteristics are explained in terms of the Pool–Frenkel and Schottky effects. The J–E relation and DC conductivity are strongly dependent on both the Li concentration and applied electric field intensity. Dielectric hysteresis was observed between heating and cooling runs which revealed that the dielectric constant often increases slowly in the low-temperature region, then increases faster above the phase transition.     

脉冲功率传输线磁绝缘的建立与特性分析

 分析了脉冲功率传输线建立磁绝缘的暂态过程,对暂态过程中传输线的击穿与磁绝缘关系、电子的分布规律及其与建立磁绝缘的关系进行了阐述。分析了磁绝缘传输线电极间的电子分布改变传输线工作阻抗值的现象,给出了传输线稳态工作阻抗的求解方法和用稳态工作阻抗计算传输线暂态工作阻抗的方法。研究了截面尺寸变化时传输线中电子的分布和电磁波传播的折反射情况。结果表明:传输线在建立磁绝缘的过程中损失电子是必然的,损失电子是建立磁绝缘的必要条件。截面半径沿轴向变化时,其工作特性与极间距的变化有关。极间距增大时,后半段的电子电流增大,使其工作阻抗增大并与前半段相等,因而在尺寸变化处不产生反射波。极间距减小时,由于后半段提前产生损失电子,因而尺寸变化处产生反射波。     

CSNS/RCS引出脉冲电源传输电缆终端绝缘技术

对脉冲电源系统72 h老练实验过程中高压电缆座打火并被击穿情况进行分析,建立高压电缆终端电场分布等效电路,推导出从电缆终端到金属屏蔽层的电势差公式,从理论上分析高压座被击穿的原因是电缆终端绝缘层未做倒角,空间电荷在此处集聚、温度升高导致的。通过定位被击穿高压座击穿孔的位置验证理论分析的正确性,最后提出高压电缆端部绝缘层处理方法,并做72 h老练实验验证了其正确性。     

Physical, electrical and dielectric properties of Ca-substituted strontium hexaferrite (SrFe12O19) nanoparticles synthesized by co-precipitation method

Calcium substituted strontium hexaferrite Ca_xSr_1−xFe₁₂O₁₉ (x=0.0−0.6) nanoparticles are synthesized by chemical co-precipitation method. The synthesized samples are characterized by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy, Transmission Electron Microscopy, DC electrical resistivity and dielectric measurements. FTIR data of uncalcined sample shows that nitrate ions are present which disappeared on calcination at 920 °C. The XRD data shows that a single hexagonal magnetoplumbite phase is formed in samples in which the calcium content, x, is ≤0.20. However, a nonmagnetic phase (α-Fe₂O₃) in addition to the hexagonal phase is also present in samples with x>0.20. The average crystallite size is found between 17 and 29 nm. The DC electrical resistivity increases with increase of calcium content up to level of x=0.2 but decreased on further addition of calcium. The enhanced resistivity of the calcium doped material has potential applications in microwave devices. The variations of dielectric constant and dielectric loss angle are explained on the basis of Maxwell-Wagner and Koops models.     

脉冲功率传输线磁绝缘的建立与特性分析

分析了脉冲功率传输线建立磁绝缘的暂态过程,对暂态过程中传输线的击穿与磁绝缘关系、电子的分布规律及其与建立磁绝缘的关系进行了阐述。分析了磁绝缘传输线电极间的电子分布改变传输线工作阻抗值的现象,给出了传输线稳态工作阻抗的求解方法和用稳态工作阻抗计算传输线暂态工作阻抗的方法。研究了截面尺寸变化时传输线中电子的分布和电磁波传播的折反射情况。结果表明:传输线在建立磁绝缘的过程中损失电子是必然的,损失电子是建立磁绝缘的必要条件。截面半径沿轴向变化时,其工作特性与极间距的变化有关。极间距增大时,后半段的电子电流增大,使其工作阻抗增大并与前半段相等,因而在尺寸变化处不产生反射波。极间距减小时,由于后半段提前产生损失电子,因而尺寸变化处产生反射波。     

Synthesis,structural and electrical properties of Ti modified Bi2Sn2O7 pyrochlore

Polycrystalline ceramic samples of Bi₂Sn_2−xTi_xO₇ (x=0.00, 0.2, 0.4, 0.6 and 0.8) have been synthesized by standard high temperature solid state reaction method. The effect of homovalent cation (titanium) substitution on the Sn-site on the structural and electrical properties of the pure Bi₂Sn₂O₇ ceramic have been studied by X-ray diffraction followed by SEM, dielectric and dc conductivity studies. The structural analysis indicates that the increase of titanium contents do not lead to any secondary phase. The frequency and temperature dependent dielectric studies have been carried out. It is found that the Ti doping reduces the material particle size. The size of the particles are strongly influenced by the addition of titanium to the system. The substitution of Ti for Sn ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The activation energies of all the compounds were calculated using the relation σ=σ₀exp(−Ea/kT).     

Diffusion of acetophenone in peroxide cross-linked cable compounds

The diffusion of acetophenone in peroxide cross-linked low-density polyethylene (LDPE) medium-voltage cable was investigated with Fourier transform infrared (FTIR) microscopy. The influence of storage under normal climate and for up to 2 years on the acetophenone profile are discussed. The diffusion rate and the coefficient of diffusion of acetophenone in cross-linked LDPE were determined. It could be shown that the coefficient of diffusion is independent of the morphology of the medium-voltage cables investigated.     

Minimizing of power loss in Li-Cd ferrite by nickel substitution for power applications

The effect of Ni substitution on the microstructure, dielectric, impedance, magnetic and power loss properties has been investigated on a series of Li_0.35-0.5xCd_0.3Ni_xFe_2.35-0.5xO₄ (0.00≤x≤0.08) ferrite prepared by citrate precursor method. Dielectric and impedance measurements have been determined in the frequency range 100 Hz-10 MHz. An enhancement in permittivity was observed with Ni concentration and exhibits the maximum value of ∼7×10³ for x=0.02 sample. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of all the samples. Power loss measurements have been carried out in the frequency range 50 kHz-5 MHz at induction condition of B=10 mT. Power loss has been found to be quite low, less than 100 kW/m³ up to 500 kHz, with the substitution of Ni in Li_0.35-0.5xCd_0.3Ni_xFe_2.35-0.5xO₄ ferrite, which is useful for technological aspects.     

Induction and control of dielectric relaxation properties in Fe-doped nonstoichiometric SrTiO3 ceramics

The dielectric properties of Fe-doped Ti-rich SrTiO₃ ceramics at both A and B sites were investigated. For A site doping, we found one structural phase transition associated with the substitution of smaller Fe ions, and two sets of dielectric relaxations ascribed to oxygen vacancies and hopping conduction between Fe²⁺ and Fe³⁺, respectively. Cole-Cole relation shows that both thermally activated dielectric relaxation behaviors mainly originate from the grain boundary. However, for B site doping, they are not observed in the measured temperature range since both the short-range diffusion of oxygen vacancies and electron conduction become the long-range migration, which indicates that the additional conductive channels are opened when Fe ion doping changes from A to B site. The results provide an experimental basis for adjusting dielectric properties in paraelectric materials.     

Dielectric,electrical transport and magnetic properties of Er3+substituted nanocrystalline cobalt ferrite

Erbium substituted cobalt ferrite (CoFe_2−xEr_xO₄; x=0.0–0.2, referred to CFEO) materials were synthesized by sol-gel auto-combustion method. The effect of erbium (Er³⁺) substitution on the crystal structure, dielectric, electrical transport and magnetic properties of cobalt ferrite is evaluated. CoFe_2−xEr_xO₄ ceramics exhibit the spinel cubic structure without any impurity phase for x≤0.10 whereas formation of the ErFeO₃ orthoferrite secondary phase was observed for x≥0.15. All the CFEO samples demonstrate the typical hysteresis (M–H) behavior with a decrease in magnetization as a function of Er content due to weak superexchange interaction. The frequency (f) dependent dielectric constant (ε′) revealed the usual dielectric dispersion. The ε′–f dispersion (f=20 Hz to 1 MHz) fits to the modified Debye's function with more than one ion contributing to the relaxation. The relaxation time and spread factor derived are ∼10⁻⁴ s and ∼0.61(±0.04), respectively. Electrical and dielectric studies indicate that ε′ increases and the dc electrical resistivity decreases as a function of Er content (x≤0.15). Complex impedance analyses confirm only the grain interior contribution to the conduction process. Temperature dependent electrical transport and room temperature ac conductivity (σ_ac) analyses indicate the semiconducting nature and small polaron hopping.