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     

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.     

纳秒脉冲下聚合物电树枝引发实验方法

 借鉴直流、交流的研究经验,比较了纳秒脉冲条件下几种不同的电树枝老化实验方法。对单针-板电极和多针-板电极在纳秒脉冲下实验结果的一致性进行考察,结果表明,多针-板电极系统可以在提高实验效率的同时保证结果的准确性。采用步进法和累加法进行了不同频率下聚苯乙烯电树枝引发实验,结果表明:两种方法得到的纳秒脉冲下聚苯乙烯电树枝引发电压-频率特性基本一致,在50~500 Hz范围内,引发电压随频率的升高而降低;在500~800 Hz范围内,引发电压随频率的升高而增加。最后讨论了对于不同脉冲功率装置中绝缘材料老化试验设计的方法。     

纳秒脉冲下聚合物电树枝引发实验方法

借鉴直流、交流的研究经验,比较了纳秒脉冲条件下几种不同的电树枝老化实验方法。对单针-板电极和多针-板电极在纳秒脉冲下实验结果的一致性进行考察,结果表明,多针-板电极系统可以在提高实验效率的同时保证结果的准确性。采用步进法和累加法进行了不同频率下聚苯乙烯电树枝引发实验,结果表明:两种方法得到的纳秒脉冲下聚苯乙烯电树枝引发电压-频率特性基本一致,在50~500 Hz范围内,引发电压随频率的升高而降低;在500~800 Hz范围内,引发电压随频率的升高而增加。最后讨论了对于不同脉冲功率装置中绝缘材料老化试验设计的方法。     

重复频率脉冲下环氧树脂电树枝引发特性

脉冲功率设备中绝缘材料的电老化特性影响它运行的可靠性、安全性及寿命。在最大幅值约34 kV、脉冲上升时间约40 ns、半高宽约70 ns的纳秒脉冲下,进行了环氧树脂在不同脉冲重复频率下(1,25,50,100,300和500 Hz)的电树枝引发特性研究。实验得出环氧树脂电树枝老化的引发电压随频率变化的规律：随着频率的升高,环氧树脂材料老化产生电树枝的形态有所变化,高频下丛林状电树枝明显增多;材料的引发电压基本随频率升高而降低,正脉冲作用下E44环氧树脂的引发电压高于负脉冲作用下的;负脉冲下E44环氧树脂的引发电压高于有机玻璃材料的。讨论分析了各种因素随频率变化对环氧树脂材料电树枝引发特性的影响,高频时空间电荷的作用明显增强。     

重复频率脉冲下环氧树脂电树枝引发特性

脉冲功率设备中绝缘材料的电老化特性影响它运行的可靠性、安全性及寿命。在最大幅值约34 kV、脉冲上升时间约40 ns、半高宽约70 ns的纳秒脉冲下,进行了环氧树脂在不同脉冲重复频率下(1,25,50,100,300和500 Hz)的电树枝引发特性研究。实验得出环氧树脂电树枝老化的引发电压随频率变化的规律:随着频率的升高,环氧树脂材料老化产生电树枝的形态有所变化,高频下丛林状电树枝明显增多;材料的引发电压基本随频率升高而降低,正脉冲作用下E44环氧树脂的引发电压高于负脉冲作用下的;负脉冲下E44环氧树脂的引发电压高于有机玻璃材料的。讨论分析了各种因素随频率变化对环氧树脂材料电树枝引发特性的影响,高频时空间电荷的作用明显增强。     

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     

非核子自由度与发展核心基本理论的ABC计划

在分析核内运动,特别是其中非核子自由度的基础上提出了一个分三步发展原子核基本理论的ＡＢＣ计划. We emphasize that to develop a fundamental nuclear theory one has to consider various non nucleon degrees of freedom in nuclei and to make the theory relatvistic.A three step ABC Plan for this Purpose is proposed. The A pan is to reform the relatiivistic hadron field theory by taking the finite baryon size into account. We call finite size baryons atoms in contrast with points. The fundamental nuclear theory in this form is therefore a quantum atom dynamics(QAD). The B plan is to reform the...     

热膨胀处理的聚丙烯蜂窝膜驻极体的压电性

研究了两种商用聚丙烯蜂窝膜(PPCellular)(EUH75和SHD50)的压电性.通过热膨胀技术处理测得上述两种商品膜的压电d33系数分别可达219pC／N和196pC／N.它们比未经处理的样品提高了约两个数量级，而比著名的铁电聚合物PVDF高出一个数量级以上.在强介电气体六氟化硫(SF6)中用高达60kV的电晕电压对EUH75和SHD50样品充电后，讨论了对其压电d33系数的影响的明显差异及其差异的结构根源. 关键词： PP蜂窝膜 压电性 热膨胀技术 介电气体     

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.     

Studies on compatibilization of polypropylene/thermoplastic polyurethane blends and mechanism of compatibilization

This paper reports a study of compatibilization and the mechanism of compatibilization of polypropylene (PP)/thermoplastic polyurethane (TPU) blends with maleated polypropylene (PP-MA) and its graft copolymer with polyethylene oxide (PEO), (PP-MA)-g-PEO. The results of scanning electron microscope (SEM) and dynamic mechanical analysis showed that (PP-MA)-g-PEO was a very good compatibilizer for PP/TPU blends, while PP-MA also produced some compatibilization. The cocrystallization between bulk PP and PP segments of the compatibilizers was evidenced by differential scanning calorimetry studies. The specific interaction between TPU and polar parts of the compatibilizers was studied with Fourier transform infrared spectroscopy.     

Analysis of electrical tree propagation in XLPE power cable insulation

Electrical treeing is one of the major breakdown mechanisms for solid dielectrics subjected to high electrical stress. In this paper, the characteristics of electrical tree growth in XLPE samples have been investigated. XLPE samples are obtained from a commercial XLPE power cable, in which electrical trees have been grown from pin to plane in the frequency range of 4000-10,000 Hz, voltage range of 4-10 kV, and the distances between electrodes of 1 and 2 mm. Images of trees and their growing processes were taken by a CCD camera. The fractal dimensions of electric trees were obtained by using a simple box-counting technique. The results show that the tree growth rate and fractal dimension was bigger when the frequency or voltage was higher, or the distance between electrodes was smaller. Contrary to our expectation, it has been found that when the distance between electrodes changed from 1 to 2 mm, the required voltage of the similar electrical trees decreased only 1or 2 kV. In order to evaluate the difficulties of electrical tree propagation in different conditions, a simple energy threshold analysis method has been proposed. The threshold energy, which presents the minimum energy that a charge carrier in the well at the top of the tree should have to make the tree grow, has been computed considering the length of electrical tree, the fractal dimension, and the growth time. The computed results indicate that when one of the three parameters of voltage, frequency, and local electric field increase, the trends of energy threshold can be split into 3 regions.     

Influence of surface modification of halloysite nanotubes and its localization in PP phase on mechanical and thermal properties of PP/ABS blends

Halloysite nanotubes (HNTs) have been successfully modified using polyethyleneimine (PEI). HNTs and PEI-modified HNTs-filled 80/20 (wt/wt) polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blends and its nanocomposites in the presence of dual compatibilizer have been prepared by melt mixing technique. The refinement in matrix–droplet morphology, selective localization of PEI-modified HNTs, increase in crystallinity of PP phase, formation of β-form of PP crystals and improved dispersion of PEI-modified HNTs in PP phase has resulted in a remarkable improvement in tensile modulus, impact strength and thermal stability of PEI-modified HNTs-filled 80/20 (wt/wt) PP/ABS blends in presence of dual compatibilizer. The increase in tensile modulus, tensile strength and impact strength for PEI-modified HNTs-filled 80/20 (wt/wt) PP/ABS blends in presence of dual compatibilizer are 28.8, 26.6 and 38.5%, respectively.     

Toward understanding the morphology-related crack initiation and propagation behavior in polypropylene systems as assessed by the essential work of fracture approach

Fracture mechanical terms related to the crack initiation and propagation, respectively, were assessed by the essential work of fracture (EWF) method for compression-molded polypropylene (PP) blends and elastomeric polypropylenes (ELPPs). The resistance to crack initiation (RCI) was characterized by the essential work of fracture w_e The w_e of the PP blends with 20 vol% ethyiene-co-butylene (EB) copolymers of various butylene (B) contents (58 and 90 wt%) and morphology (EB58 is amorphous, whereas EB90 is semicrystalline) increased with increasing butylene content and thus crystallinity. At the same time, in the slope of the EWF resistance curves, which inform about the resistance to crack propagation (RCP) of the PP/EB blends, an adverse change was observed. For the ELPPs of various crystallinity and morphology, the opposite tendency was found, that is, the RCI decreased, but the RCP increased with increasing crystallinity. The above findings were interpreted by considering the morphology and its rearrangement due to loading. It was suggested that the RCI is improved by the order of the crystalline structure and by the density of tie molecules that transfer the stress from the amorphous toward the crystalline phase. On the other hand, the RCP is controlled by a stress redistribution process that is influenced by possible changes in the local morphology.     

Thermosets as compatibilizers at the isotactic polypropylene film and thermomechanical pulp fiber interphase

The objective of this study was to improve interfacial adhesion properties at the interface of thermomechanical pulp (TMP) fiber and isotactic polypropylene (iPP) using thermoset adhesives such as phenol formaldehyde (PF) and urea formaldehyde (UF). This study also attempted to achieve fiber-to-fiber adhesion using thermoset adhesives before the molten iPP would flow into the fiber web. The fracture surfaces with thermoset adhesive showed identical differences in terms of fracture modes at the interface. An increased TMP fiber failure was observed with increased thermoset quantity at the interface. Using one percent resin content of weight fraction of TMP fiber handsheet, the tensile strength properties increased almost two fold higher than the strength of control samples. Additional adhesive contents of three and five percent showed gradual strength enhancement. However, the enhanced strength was statistically insignificant. UF resin showed slightly better strength performance over PF resin. This result may be caused by solid contents and additional pigments of resins.     

Polymer-filler interaction and control of structure in barium sulphate-filled blends of polypropylene

The structure of barium sulphate-filled immiscible blends with a polypropylene (PP) matrix can be controlled with respect to the occlusion of the filler with the aid of maleic anhydride-grafted polypropylene (PP-g-MAH) through the formation of an interlayer around the filler particles. Here we analyze the interlayer and the mechanism of interlayer formation in a blend with a poly(methylmethacrylate) (PMMA) dispersed phase and compare the results with previous studies, which concerned PP blends with polystyrene (PS) and poly(styrene-co-acrylonitrile) (SAN) minority phases. The main analytical tools were scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and Fourier Transform Infrared Spectroscopy (FTIR). The filler is occluded in the PMMA polymer in the PP/PMMA/BaSO₄ (60/20/20 vol.%) blend, but is occluded in the PP phase at the addition of a sufficient amount of PPg-MAH. The reason for the formation of the latter structure is a PP-g-MAH layer surrounding the filler particles, and the most likely mechanism behind this phenomenon is judged to be specific weak interactions between carbonyl groups in the graft copolymer and Ba²⁺ ions at the filler surface.     

Self-sustained firing activities of the cortical network with plastic rules in weak AC electrical fields

Both external and endogenous electrical fields widely exist in the environment of cortical neurons. The effects of a weak alternating current (AC) field on a neural network model with synaptic plasticity are studied. It is found that self-sustained rhythmic firing patterns, which are closely correlated with the cognitive functions, are significantly modified due to the self-organizing of the network in the weak AC field. The activities of the neural networks are affected by the synaptic connection strength, the external stimuli, and so on. In the presence of learning rules, the synaptic connections can be modulated by the external stimuli, which will further enhance the sensitivity of the network to the external signal. The properties of the external AC stimuli can serve as control parameters in modulating the evolution of the neural network.     

The surface alloying behavior of martensitic stainless steel cut with wire electrical discharge machine

The surface alloying behavior of tempered martensitic stainless steel multi-cut with wire electrical discharge machine (WEDM) is studied in this paper. Before machined with WEDM, the steel specimens were quenched at 1050 °C and then tempered at 200 °C, 400 °C, and 600 °C, respectively. The microstructure and surface morphology of the multi-cut surfaces were examined with scanning and transmission electron microscopes integrated with an energy-dispersive X-ray spectrometer for chemical composition analysis. Experimental results show that the cut surfaces of the steel specimens were alloyed with wire-electrode material in various extent. Especially the cut surface was much more alloyed when the steel was cut with the first rough cutting pass by using negatively biased potential and final fine cutting using positively biased potential. Alloying degree of cut surfaces can be distinguished with their anodic polarization curves in 0.5 M HClO₄ + 0.2 wt% NaCl at 27 °C. Higher passive current density induces deeper alloyed surface. On the severely alloyed surface, a secondary anodic peak in the potential of 120 mV (versus Ag/AgCl_sat.) of its anodic polarization curve was observed. The presence of the secondary anodic peak was attributed to dissolution of copper, which was the major element of wire-electrode material from the alloyed surface.     

丝电爆过程的电流导入机理

丝电爆制备纳米粉时, 电流从电极导入金属丝的过程直接影响电极烧损和粉末中微米级大颗粒产生. 分别通过接触和气体放电两种方式导入电流进行电爆试验. 结果表明, 光测量装置检测到的丝端部光电流几乎与回路放电电流同时产生, 而中间位置的光电流则要滞后一段时间; 由探针收集的产物确定, 金属丝端部主要形成熔融粒子, 中间部分主要形成气相粒子. 分析可知, 接触方式导入电流时, 丝端部也存在气体放电现象, 大电流主要通过气体放电形成的等离子体导入. 等离子体对电流的旁路作用会阻碍能量向金属丝沉积, 这是产生微米级大颗粒和"积瘤"主要原因. 通过气体放电方式导入电流时, 电极烧损明显减轻, 并可以避免"积瘤"产生.