High‐field electrical properties of new LDPE films prepared using metallocene catalyst

Now low‐density polyethylene (M‐LDPE) prepared using metallocene catalyst has narrower composition distribution and molecular weight distributions than linear low‐density polyethylene (LLDPE) using Ziegler catalyst. The authors compared the electrical insulating properties of M‐LDPE films and conventional LLDPE films. The high‐field current of M‐LDPE was found to be lower than that of LLDPE. The difference in current increased with the decrease of temperature. The high‐field current was much reduced in M‐LDPE with a low melting point. The impulse breakdown strength of M‐LDPE increased with the decrease of temperature. The insulating properties of M‐LDPE with a low melting point were improved at 30 °C. These results were explained by the fact that M‐LDPE with a low melting point includes more low‐molecular‐weight components. We also discuss the effects of antioxidant on the electrical properties of M‐LDPE. We compared the electrical conduction and breakdown strength of undoped M‐LDPE and antioxidant‐doped M‐LDPE. Differences in their electrical properties were minor. It was found that the excellent properties of M‐LDPE do not depend on the effects of antioxidant. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 1–9, 2000     

A consideration of potentials of low‐density polyethylene using metallocene catalyst as insulator for power cable

We investigated the high‐field conduction, DC and impulse breakdown strength, space charge distribution, and tree inception voltage for three kinds of new low‐density polyethylene (LDPE) prepared using a metallocene catalyst (mLna, mLao, mLldao), linear LDPE prepared using a Ziegler catalyst (LLao), and LDPE prepared by a high‐pressure process (LDna). The dc and impulse breakdown strengths of LDPEs prepared using a metallocene catalyst were higher than those of LLao and LDna. The high‐field currents of LDPEs prepared using a metallocene catalyst were lower than those of LLao and LDna. A homo‐space charge was accumulated near the cathode in mLna. The tree inception voltage of mLna was higher than that of LDna. From these results, it is concluded that LDPE prepared using a metallocene catalyst has electrical insulating properties superior to the conventional LDPE and that the former has potential as a power cable insulator. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 17–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1164     

电声脉冲法测量聚合物绝缘表面陷阱能级分布

对紫外光老化不同时间的低密度聚乙烯(low-density polyethylene,LDPE)试样及3%含量的纳米氧化锌(ZnO)粒子与LDPE复合材料试样进行了交流击穿实验,结果表明纯LDPE试样的击穿强度随光老化时间的增加逐渐降低,3%含量的纳米ZnO粒子与LDPE复合材料的击穿强度光老化后基本保持不变。通过对老化前后试样的老化面分别进行电晕放电注入负电荷,并采用电声脉冲法测量短路状态下表面注入电荷随时间的衰减特性,通过公式推导计算得出试样老化面的陷阱能级分布。结果表明,纳米ZnO粒子不仅能提高聚乙烯的光稳定性,还通过成核和界面作用减少聚乙烯体内深陷阱密度,增加浅陷阱密度。     

A wave‐front‐time dependent corona model for transmission‐line surge calculations

For transmission‐line surge studies, the inclusion of corona discharge due to high voltage surges is important as well as the inclusion of frequency‐dependent effects. Because the charge‐voltage (q‐v) curve of a lightning surge is different from that of a switching surge, a corona model should reproduce different q‐v curves for different wave‐front times. The present paper proposes a wave‐front time dependent corona model which can express the dependence by a simple calculation procedure as accurately as a rigorous finite‐difference method which requires an enormous calculation time. The simplicity enhances the incorporation of the corona model into a line model, because a large number of models are to be inserted into the line model by discretization. The q‐v curves calculated by the proposed method agrees well with field tests. This paper also proposes an efficient method to deal with nonlinear corona branches in distributed‐parameter line model using the trapezoidal rule of integration and the predictor‐corrector method. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 29–38, 1999     

热老化前后LDPE/SiO2纳米复合材料空间电荷积聚分析

在实际运行中,直流场强和热环境都会对聚乙烯电缆内空间电荷积聚行为产生影响,过量的空间电荷会威胁其绝缘性能,虽然纳米复合材料具备抑制空间电荷的能力,但对于热老化后其空间电荷的积聚特性仍有待进一步研究。采用电声脉冲法对热老化前后不同浓度的低密度聚乙烯(LDPE)/二氧化硅(SiO_2)纳米复合材料内空间电荷的积聚行为进行分析。结果表明,热老化会降低电极注入势垒并产生随机分布的深陷阱和杂质,增加空间电荷积累。纳米SiO_2引入的大量界面区域会产生均匀分布的深陷阱,并形成界面反电场,从而抑制载流子的运输和注入,且纳米粒子可以提高材料稳定性,提升电极注入势垒并延缓热老化进程。相比于纯LDPE,LDPE/SiO_2材料在热老化前后都具有明显的抑制空间电荷的能力。     

Vertical‐type organic device using thin‐film ZnO transparent electrode

We propose a double heterojunction organic light‐emitting diode (OLED) using a zinc oxide (ZnO) film, which works as a transparent and electron injection layer. The crystal structure of the ZnO films as a function of Ar/O₂ flow ratio and the basic characteristics of the OLED depending on the ZnO sputtering conditions are investigated. Excellent characteristics of the novel OLED were obtained, as high as 470 cd/m² at 22 V and 7.6 mA/cm². The results obtained here demonstrate that the vertical organic light‐emitting transistor (OLET) using a ZnO layer as an electron injection layer is promising as a key element for flexible sheet displays. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 49–55, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20151     

热老化条件下LDPE/TiO2纳米复合材料介电特性研究

电力电缆在运行过程中普遍存在的热老化现象容易加速绝缘失效,限制设备使用寿命,甚至引发电力系统故障。纳米粒子掺杂改性可以提高聚乙烯基体材料的热稳定性,开展相关研究可以为提高电缆绝缘寿命提供解决方案。以低密度聚乙烯(LDPE)/二氧化钛(Ti O_2)纳米复合材料为研究对象,分别研究了热老化条件下纳米粒子质量分数、老化时间、老化温度对材料介电特性的影响。实验结果表明,掺杂Ti O_2纳米粒子能够改善LDPE基体材料的介电特性,当Ti O_2纳米粒子填充质量分数为0.5%时,纳米复合材料介电特性最佳。老化时间和老化温度是影响材料介电特性劣化的两个重要因素,随着老化时间推移和老化温度提高,纳米复合材料的介电性能劣化现象越明显。对聚乙烯材料进行纳米改性的同时降低电缆运行环境温度,对提高电缆绝缘寿命具有重要意义。     

Effects of inorganic fillers on withstanding short‐time breakdown and long‐time electrical aging of epoxy composites

Inorganic fillers were added to epoxy resin for preparing micro and nano filler/epoxy composite, and then the breakdown strengths, depths of erosion caused by partial discharge, and electrical tree experiments of composites were investigated. It was found that the loading of micro fillers usually decreases the short‐time breakdown strength (breakdown under a continuously rising voltage) of the composites. On the contrary, it increases the ability to withstand long‐time electrical aging (erosion or breakdown caused by electrical tree under a discontinuously rising voltage or constant voltage) of the composites. The effect of inorganic fillers in suppressing the electrical tree or erosion channel propagation in the composite is different during the process of withstanding short‐time breakdown and long‐time electrical aging. Defects are introduced during the mixing of fillers and epoxy resin, which play a role to decrease the short‐time breakdown strength and accelerate long‐time electrical aging. It is concluded that micro and nano inorganic fillers can suppress the electrical tree channel propagation and erosion caused by partial discharge, whereas defects play the opposite role in composites. Two opposite effects of inorganic fillers and defects exist simultaneously during the process of electrical aging and breakdown; whereas inorganic fillers play a primary role in long‐time electrical aging, defects play a primary role in short‐time breakdown.     

LDPE/MVQ并用胶的组份对其热老化性能的影响

在室温下实现甲基乙烯基硅橡胶(MVQ)和沉淀法白炭黑(SiO2)的共混,制备出MVQ混炼胶。在150~180℃下实现MVQ混炼胶和低密度聚乙烯(LDPE)的熔融共混,制备出LDPE/MVQ并用胶。研究结果表明,随着SiO2含量的增加,LDPE/MVQ并用胶的耐空气热老化性能下降;羟基硅油对材料的热老化性能影响不明显,但甲基乙烯基硅油可显著改善材料的热老化性能;随着LDPE与MVQ混炼胶的质量比的增加,材料的耐热老化性能下降。     

Transient phenomena of current and field distortion due to dynamics of packet‐like charges in LDPE films

Simultaneous measurements of space charge and external current were carried out using a PEA measurement system with an electrometer on the back of a grounding electrode in order to clarify the physical situation of a huge packet of positive space charges in LDPE films. A large number of positive charges from a semiconducting anode were accumulated at the interface between LDPE and an Al‐cathode at a mean applied field of 1.5 MV/cm and then finally disappeared. The results of simultaneous measurements showed that the external current kept a relatively high value during charge accumulation and further increased when the charges disappeared. Both the charge dynamics and the external current were restricted by addition of a low‐molecular‐weight paraffin wax, indicating that carrier transport was influenced by the microstructure of the polymer. The dynamics of the residual charges after short‐circuiting is also discussed. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(4): 10–17, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21256     

High‐field electrical properties under AC voltage application in acetophenone‐coated LDPE film

This paper deals with the effects of acetophenone coating on dielectric properties such as tan δ and capacitance and on space charge formation up to electrical breakdown under AC voltage application in low‐density polyethylene (LDPE) film. The existence of acetophenone at the electrical interface enhances tan δ. tan δ in acetophenone‐coated specimens increased with electric field and decreased with the frequency in the high‐field and high‐temperature region. AC breakdown test revealed that the electric strength in noncoated specimens was higher than in acetophenone‐coated specimens, and that the electric strength also decreased with temperature. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 1–7, 2003; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.10086     

低密度聚乙烯/纳米蒙脱土复合材料的水树枝生长特性

低密度聚乙烯是高压电力电缆的主要绝缘材料,水树枝生长特性与聚乙烯高压电力电缆绝缘击穿具有紧密联系。采用熔融插层复合法制备了一种低密度聚乙烯/蒙脱土纳米复合材料;设计制作了纳米复合材料的水树枝老化试样及试验装置,在试验中观测了试样的水树枝生长长度,并对试样的水树枝引发率进行了统计,分析了低密度聚乙烯/蒙脱土纳米复合材料的吸水率对水树枝生长的影响;采用差示扫描热法分析了试样的结晶度和晶粒尺寸均匀性,通过分析低密度聚乙烯/蒙脱土纳米复合材料的结晶行为,说明了纳米蒙脱土对纳米复合材料中水树枝的抑制机理。试验与分析结果表明:掺杂质量分数为3%的纳米蒙脱土粒子能够有效地提高低密度聚乙烯的结晶度,使晶粒尺寸分布均匀,吸水率减小,延缓水树枝在低密度聚乙烯中的引发与生长。     

Dielectric behavior of aged polyethylene under UV radiation

The present paper reports the results of a study of dielectric aging of low-density polyethylene (LDPE) by UV radiation. The extruded polymer contained carbon black particles, approximately 3% in weight. The aging studies were made for polymer without and with carbon black. LDPE flat specimens were aged under UV radiation for up to 300 h, resorting to dielectric spectroscopy measurements in the frequency range from 10/sup -5/ Hz to 10/sup 5/ Hz. The dielectric susceptibility behaviors indicate the presence of relaxation peaks obeying the asymptotic forms of Dissado and Hill susceptibility functions. As the aging progresses, quasi-DC and flat loss processes may be observed in the low frequency range, for the LDPE specimens without and with carbon black, respectively. In addition, dielectric spectroscopy results have been compared with other results obtained with additional techniques such as Fourier transform infrared spectroscopy and scanning electron microscopy.     

纳米MgO掺杂聚乙烯中空间电荷行为的研究

介绍了采用电声脉冲法测量纯低密度聚乙烯以及氧化镁／低密度聚乙烯（MgO／LDPE）纳米复合介质中的空间电荷,讨论了不同含量的MgO以及不同型号LDPE作为基础材料对复合介质内空间电荷分布的影响。实验结果表明：随着直流电场的增加,在纯聚乙烯中产生电荷注入现象,且随着加压时间的增加,注入的同极性电荷有向另一电极移动的趋势。少量的MgO可以有效抑制复合介质中的空间电荷注入,随着MgO含量的增加,对复合介质的空间电荷注入抑制效果逐渐减弱。     

Suppression of electrical treeing by addition of lithium carbonate to low-density polyethylene

Low-density polyethylene (LDPE) is used widely as an electric insulating material in electric power cables. The generation of electrical treeing due to aging of LDPE may lose the reliability of its insulating capability. Therefore it is important to suppress its treeing and to improve its electrical properties so that the reliability of cables can be improved. For this purpose, the authors prepared LDPE to which various inorganic materials were added. This investigation focuses particularly on lithium carbonate and quartz which were effective in suppressing the treeing when added to LDPE. Lithium carbonate-added (0.25 phr) LDPE in two hours of discharge showed the tree length 150 μm shorter than that (560 μm) of nonadded LDPE, exhibiting an obvious suppressing effect on treeing generation. It was found that this effect was more significant than quartz-added LDPE and even at elevated temperatures lithium carbonate-added LDPE exhibited suppression of treeing. The thermal decomposition temperature at which lithium carbonate-added (1 phr) LDPE loses 50 percent of its weight rose 100°C more than nonadded LDPE and 60°C more than that of quartz-added LDPE, which showed improvement in heat resistance of LDPE.     

纳米ZnO/低密度聚乙烯复合材料的介电特性

聚合物纳米复合材料因其优良的介电、机械等性能在电介质领域得到广泛的应用。纳米粒子改性聚乙烯基绝缘材料具有很好的研究价值及工程意义。该文主要研究了表面经分散剂处理的纳米ZnO粒子添加剂与低密度聚乙烯(LDPE)共混物的介电特性。结果表明5%含量的纳米ZnO添加剂能有效提高聚乙烯基复合材料的体积电阻率和交流击穿强度。同时纳米添加剂虽增加了体内的残余电荷,但能有效抑制电极同极性电荷的注入。另外由于聚合物纳米复合材料的界面特异性,使得介电常数随着纳米ZnO含量的增加呈先减小后增大趋势,而损耗值却线性增加。纳米ZnO/聚乙烯复合材料介电性能提高归因于纳米粒子与聚乙烯分子间类同于深陷阱的界面效应。     

Conductivity of carbon black-PE composites as a function oftemperature and UV aging

We performed a study of mechanisms related to ac electrical conductivity of virgin and aged low-density polyethylene (LDPE) loaded with different concentrations of carbon black (CB). Experimental ac conductivity measurements were carried out at different temperatures on samples with different CB concentrations. Scanning calorimetry (DSC) and thermal expansion measurements were used as auxiliary techniques in this study. We also investigated the aging effect of UV radiation on the electrical properties of the samples. Based on the distribution of the CB in the polyethylene matrix, the ac conductivity is explained in terms of the hopping mechanism considering the material as a system where the energy potential barriers are distributed randomly in the bulk of the material     

Properties of Space Charge Distributions and Conduction Current in XLPE and LDPE under DC High Electric Field

Space charge behavior and conduction current in polyethylene under dc stress were investigated. One of the reasons for the different breakdown property in cross‐linked polyethylene (XLPE) from that in low‐density polyethylene (LDPE) may be based on the existence of cross‐linking by‐products in XLPE. Furthermore, a thermal history in cross‐linking process for XLPE may also cause of the difference. It is generally accepted that the existence of the cross‐linking by‐products increase the conduction current in XLPE under dc stress. It is also said that an anneal treatment in air atmosphere may affect to the electrical properties under dc stress. Therefore, we investigated the effect of the cross‐linking by‐products and the anneal treatment on space charge behavior and conduction current in polyethylene under dc stress. In our research, it is thought that the increasing dissipation power in XLPE is the cause of the breakdown in it under dc stress. Therefore, to calculate the dissipation power in the bulk of test sample, we measured the space charge distribution and the external circuit current simultaneously. Based on the results, we discussed the reason of the difference of the space charge properties in XLPE and LDPE focusing on the cross‐linking by‐products and the oxidation of the test samples.     

A switch‐utilization‐improved switched‐inductor switched‐capacitor converter with adapting stage number

A novel closed‐loop switched‐inductor switched‐capacitor converter (SISCC) is proposed by using the pulse‐width‐modulation (PWM) compensation for the step‐up DC–DC conversion/regulation, and together by combining the adaptive‐stage‐number (ASN), control for the higher switch utilization and wider supply voltage range. The power part of SISCC is composed of two cascaded sub‐circuits, including (i) a serial‐parallel switched‐capacitor circuit with n_c pumping capacitors and (ii) a switched‐inductor booster with m_c resonant capacitors, so as to obtain the high step‐up gain of (n_c + 1) × m_c /(1 ? D) at most, where D is the duty cycle of PWM adopted to enhance output regulation as well as robustness to source/loading variation. Besides, the ASN control is presented with adapting the stage number n (n = 0, 1, 2, …, n_c) of pumping capacitors to obtain a flexible gain of (n + 1) × m_c /(1 ? D), and further in order to make the SISCC operating at a properly small duty cycle for improving switch utilization and/or supply voltage range. Some theoretical analysis and control design include formulation, steady‐state analysis, ASN‐based conversion ratio, efficiency, output ripple, stability, inductance and capacitance selection, and control design. Finally, the performance of this scheme is verified experimentally on an ASN‐based SISCC prototype, and all results are illustrated to show the efficacy of this scheme. Copyright © 2015 John Wiley & Sons, Ltd.     

纳米ZnO对聚乙烯电老化过程中空间电荷及击穿特性的影响

聚乙烯是电气绝缘领域应用最广泛的聚合物材料之一。根据电老化过程中电子和空穴复合产生的紫外辐射能导致聚合物降解理论,将少量纳米ZnO与低密度聚乙烯熔融共混,研究了电晕老化不同时间后复合材料空间电荷以及击穿特性的变化。结果表明添加纳米ZnO能有效提高聚乙烯绝缘的耐电晕老化寿命。