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     

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 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     

Analysis of the current distortion factor of a three‐phase,three‐wire system

In a balanced three‐phase system, the three‐phase current distortion factor of three‐phase ac power sources has been expressed by applying the conventional single‐phase current distortion factor, which is defined for a single‐phase system. However, in an unbalanced three‐phase system, it is difficult to express the three‐phase current distortion factor for distorted three‐phase ac currents by means of the conventional single‐phase current distortion factor. For instance, the conventional current distortion factors for three‐phase ac currents are usually different from each other in the unbalanced three‐phase system. To solve the above problem, this paper proposes a novel definition of the three‐phase current distortion factor. The proposed three‐phase current distortion factor is quite effective for the unbalanced three‐phase system as well as the balanced three‐phase system. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 1–10, 2000     

Thermally stimulated current and thermally stimulated charge distribution in electron‐beam‐irradiated PMMA

The relationship between the external current J_ter(t), the conduction current J_c(x, t), and the displacement current ϵ∂E(x, T)/∂t of an electron‐beam‐irradiated PMMA is discussed in terms of measurements of the thermally stimulated current (TSC) and the thermally stimulated space charge distribution (TS‐SCD). ϵ∂E(x, T)/∂t is calculated from TS‐SCD measurements obtained with an improved pulsed electroacoustic (PEA) system. By virtue of the conservation of charge, J_c(x, t) is easily calculated from the measured J_ter(t) and the calculated ϵ∂E(x, T)/∂t. In this report, an approach to the conduction current analysis using the theory of conservation of charge is described and an analysis of the conduction current in an electron‐beam‐irradiated PMMA is introduced as a typical example. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 1–6, 1999     

MgO/LDPE纳米复合材料制备及其空间电荷特性

为了降低低密度聚乙烯中的空间电荷积累,在自制纳米MgO粉体的基础上,采用熔融共混法,制备了氧化镁/低密度聚乙烯（MgO/LDPE）纳米复合材料,并通过扫描电镜（SEM）观察了MgO/LDPE纳米复合材料中的MgO粒径大小和分散情况,采用差热扫描量热法（DSC）确定了不同MgO质量分数纳米复合材料的结晶度,采用电声脉冲法（PEA）测量了不同MgO质量分数纳米复合材料的空间电荷分布,测量了不同MgO质量分数纳米复合材料的拉伸性能。试验结果表明,MgO/LDPE纳米复合材料体系中,MgO粒径约为50nm,且分散均匀;不同MgO质量分数纳米复合材料的弹性模量和抗张强度均高于纯LDPE的,且MgO质量分数为2%时达到最大值;不同MgO质量分数纳米复合材料的结晶度均高于纯LDPE的;纳米MgO能抑制空间电荷的注入和其在材料体内的迁移,质量分数为3%时,MgO/LDPE纳米复合材料中的空间电荷得到了良好的抑制。     

汽轮发电机在饱和与磁场畸变时负载励磁电流计算的新方法

磁路饱和与磁场畸变的共同作用会使发电机负载饱和特性显著偏离其空载特性,为了计算这种差异,提出了其负载励磁电流计算的一种改进方法.以300 MW汽轮发电机为例,以有限元方法为工具,获得了反映磁路饱和与磁场畸变共同作用下负载非线性特性的关系曲线族,提出了用这种新曲线族代替空载特性计算负载励磁电流的新方法.通过计算发电机在不同功角下的负载励磁电流,说明该方法比传统方法有较高的计算精度,比有限元方法有较快的计算速度.     

导电碳黑填充EVA半导电电极对聚乙烯中空间电荷注入的影响

为探索导电碳黑填充EVA半导电电极对聚乙烯中空间电荷注入的影响,分别将碳黑以3种不同的比例填充到EVA中作为聚乙烯的电极,碳黑的体积分数分别为27％,32％和34％。高压下,采用压力波法研究聚乙烯中空间电荷的注人情况,并对测量结果进行定性的比较和分析。结果表明,聚乙烯样品中空间电荷的注入量随着电极中碳黑填充率的增大,空间电荷的注入量反而减小。这与理论预测相符,电极中碳黑的填充率越大,与聚合物接触的界面处碳黑颗粒的排列就越密集,颗粒表面最高场强就越低,且表面局部高场区在平均场强的延伸范围就越小,从而就减少了空间电荷的注入。     

茂金属聚乙烯改性低密度聚乙烯中空间电荷的机理研究

针对高压,超高压直流塑料电缆中存在的空间电荷效应,文中选用与普通低密度聚乙烯(LDPE)化学结构相似的茂金属聚乙烯(MPE)作为成核剂与LDPE共混,用电声脉冲法(PEA)测量了共混物的空间电荷特性,以差示扫描量热法(DSC)研究了共混物的非等温结晶行为,用高阻计测量了共混物的体积电阻率的变化,结合聚合物的结晶和导电理论,讨论了共混物中空间电荷的形成和抑制机理。测试结果表明:1%的MPE与LDPE共混,能有效降低LDPE中空间电荷效应,提高结晶温度,降低体积电阻率。     

不同表面处理剂对纳米MgO/LDPE空间电荷行为的影响

为研究不同表面处理剂对纳米MgO/低密度聚乙烯(LDPE)复合介质空间电荷行为的影响,将经过不同表面处理的纳米MgO颗粒以不同质量分数填充到低密度聚乙烯中,制得纳米复合介质,并对不同纳米复合介质的微观特性结构和空间电荷分布进行了实验研究。微观特性研究表明,经过表面处理,无机纳米颗粒与聚合物的结合作用得到增强,复合介质结晶度增加;空间电荷实验表明,添加经过不同表面处理的纳米MgO后复合介质在短路时阴极和阳极均积累了同极性电荷。此外,在不同无机纳米颗粒填充质量分数下,经过不同表面处理剂修饰后的纳米复合介质内部积累的空间电荷得到不同程度的抑制。总体而言,铝酸酯偶联剂对纳米MgO颗粒的表面处理效果相对较好。     

Preparation and functions of conductive polymer/insulating polymer composite films using molecular self‐assembly

By exposing low‐density polyethylene to an atmosphere of fuming sulfuric acid, sulfonated low‐density polyethylenes (SPE) were prepared and the degree of surface sulfonation of the treated film was determined from the weight increase per unit area. Polypyrrole (PPy) films on the surface of SPE were grown by molecular self‐assembly and the properties of PPy/SPE composite films were investigated. Functional applications of PPy/SPE composite films are proposed, with particular attention to the movement properties of actuators using PPy/SPE composite films. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 1–8, 1999     

Development of a high‐pressure air‐insulated 72/84‐kV disconnecting switch corresponding to bus‐transfer current switching

SF₆ gas has excellent dielectric strength and current interruption performance. For these reasons, it has been widely used for gas‐insulated switchgear (GIS). Today, such global environmental problems as global warming are important issues of concern. SF₆ gas is known as a greenhouse gas with a long atmospheric lifetime, and has global warming potential of 23,900. SF₆‐free 72‐kV GIS was recently developed by using high‐pressure air and a gas/solid hybrid structure. But an alternating current disconnecting switch (DS) has yet to be developed thus making this type of SF₆‐free 72‐kV GIS unsuitable for double bus‐bar application. Consequently, the development of a high‐pressure air‐insulated DS corresponding to bus‐transfer current switching has been expected. The bus‐transfer current is the highest among all current interruption requirements for the DS. To develop an alternating current DS, efforts must be made to reduce arcing damage to the electrode. This paper describes the fundamental characteristics of current interruption in the plain break type and the magnetic field driven type. Then, average arcing time of the magnetic field driven type was estimated by magnetic flux density. Finally, two types of DS, which were a high‐speed plain break and a low‐speed magnetic field driven, were confirmed to comply with bus‐transfer current switching requirements on JEC standard. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 48–55, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20595     

Discussion of electrode conditioning mechanism based on pre‐breakdown current under nonuniform electric field in vacuum

Electrode conditioning is a very important technique for improvement of the insulation performance of vacuum circuit breakers (VCBs). This paper discusses the spark conditioning mechanism under a nonuniform electric field, focusing on the pre‐breakdown current. We quantitatively evaluated the spark conditioning effect by analyzing the pre‐breakdown current based on the Fowler‐Nordheim equation. The field enhancement factor β was found to decrease with increasing breakdown voltage at the beginning of the conditioning process, and finally became saturated with the saturation of the breakdown voltage. In addition, in the case of a nonuniform field, we found that β on a high‐voltage rod electrode after conditioning varied according to the electric field strength on the rod electrode. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(2): 21‐28, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21059     

Rocket‐triggered lightning current waveforms in winter and investigation of extra‐fast current change

Since 1986, the authors have been taking part in triggered lightning experiments in winter, at Okushishiku, Ishikawa, for the purpose of observing the entire lightning current waveforms with coaxial shunt resistors and an electro‐optical measuring system. Extra‐fast current changes of the order of 1,000 kA/μs were recognized by sharp pulse records superposed on the positive current waveform obtained by a shunt resistor of relatively high residual inductance. This was not the case with a resistor of lower inductance. Furthermore, a positive lightning current waveform which looks like the composite result of bi‐polar discharges has been observed by an advanced measuring system of high performance. This paper deals with these current‐related topics of triggered lightning discharges, which will be analyzed hereafter in detail. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 18–23, 1999     

Study on dependence of AC transport current losses in YBCO‐coated conductors on distribution of critical current density and n value

We measured AC transport current losses in three kinds of thin‐film YBCO‐coated conductors made by different processes. The results showed that the loss characteristics were different and that some of the conductors did not follow the Norris strip model which is generally believed to well explain the loss characteristics of YBCO conductors. In the paper, an analytical model in which distribution of critical current density and n value of the conductor are taken into consideration is proposed to describe the AC transport current loss characteristics more generally than the Norris strip and elliptical models. It is shown that the analytical model explains well the measured loss characteristics of the three kinds of conductors. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 26–38, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20056     

Optimal current control methods of a non‐salient pole hybrid field‐synchronous motor for energy‐efficient and wide speed‐range operation

This paper proposes new practical optimal current control methods for a newly emerging class of non‐salient pole synchronous motors with hybrid rotor fields by both permanent magnet and winding. In practical situations with limited voltage, the extensively used permanent magnet synchronous motor hardly achieves an ideal performance that allows simultaneously both low‐speed high‐torque and wide speed‐range operations, due to its constant magnet field. Hybrid field synchronous motors (HFSM) have recently emerged to achieve ideal performance as practical motors with controllable hybrid rotor field. For HFSM, the same torque can be produced by a variety of currents due to nonlinearity between torque and currents. Consequently, appropriate determination of a set of stator and rotor current commands plays a key role in achieving possible energy‐efficient and wide speed‐range operation. Proposed methods determine the current commands corresponding to a given torque command such that total winding copper loss due to stator and rotor currents can be minimized if the exact solution exists; the best approximate torque can be produced if no exact solution exists. The determined current commands are optimal in the sense of energy efficiency or degree of approximation in wide speed‐range operation under voltage limit. New real‐time recursive algorithms searching the optimal current solution are also given. The proposed methods are analytical but practical, and their usefulness is verified through experiments. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 70–83, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20156     

Development of NbTi superconducting strands and cables for the field winding of a 200‐MW‐class high‐energy‐density superconducting generator

The NbTi superconducting strands and cables for the field winding of the 200‐MW‐class high‐energy‐density‐type superconducting generator are developed. They are composed of Cu/Cu‐10wt%Ni/Nb‐46.5wt%Ti superconducting strands and the 10‐kA (at 5 T)‐class 9‐strand compacted cables. The diameter of strands is 1.33 mm, and the 9‐strand compacted cables are 2.4 mm thick and 6.0 mm wide. In order to produce high‐current‐density NbTi strands, we made strands under controlled aging heat treatments, the total and final strains, and the strains between heat treatments, by using large‐scale extruder. Moreover, in order to produce high‐stability and low‐AC‐loss NbTi strands and cables, the matrix ratio of strands and the cross sections of strands are optimized. The current density of NbTi filaments for the four‐time‐aging manufactured 1.33‐mm‐diameter strands was J_C=3150 A/mm² at 5 T, 1150 A/mm² at 8 T. The critical current of the 9‐strand compacted cable is 10.7 kA at 5 T. The AC losses of the final compacted cables are less than 100 kW/m³ at 5 T, 5 T/s, that is, decreased to less than half of the target of the AC loss value (< at 5 T, 5 T/s). Compared with the strand (Cu ratio 1.77), the minimum quench energy (MQE) of the strand (Cu ratio>2) increased about 40% at the operation mode current of the superconducting generator. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(3): 24– 31, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20266     

Space charge behavior in polymer film based on increment of capacitance under AC high field

Polymer materials have excellent dielectric and insulation properties; however, those properties in AC high field region have not been known well. Recently we established an evaluation method of high‐field AC dissipation current waveform of polymer materials 1 . AC dissipation current waveforms of polyethylene and polypropylene films show nonlinear distortion in AC high‐field region. This nonlinearity was thought to be related to the behavior of AC space charge formation in the sample near electrodes. The properties of space charge formed under AC high field at power frequency seem to differ from those formed under DC high field. The measurement of AC space charge distribution is not so easy due to the resolution limit of the space charge measurement. We studied the dielectric properties of biaxially oriented polypropylene (BOPP) film under AC high field up to 120 °C. It was found that tan δ, AC dissipation current (Ixr), and unbalanced component of capacitive current (ΔIxc) increased when the temperature became higher. In particular, ΔIxc increased above some threshold field and was considered to be due to the AC space charge formation. This AC space charge layer near electrode is thought to be formed due to carrier injection under AC high‐field application. Usually, the carrier mobility becomes smaller on lowering the temperature. Most of the carriers injected from the electrode are trapped near the electrode in the sample film. But in the high‐temperature region, the carrier mobility becomes larger and the carrier injection starts to increase from lower field. Many more carriers are injected from the electrode. It is thought that some of the injected carriers are trapped inside the sample film; the others go through the sample to the opposite side. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 8–16, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10018     

10 kV配电网合环电流暂态过程的分析与仿真

分析了配电网合环暂态过程及合环冲击电流对电网安全运行的影响.结合配电网特点建立了数学模型,推导出了合环冲击电流的数学表达式,并应用PSCAD/EMTDC软件对实际算例进行了暂态仿真计算.仿真计算结果表明,建立的数学模型正确可行.     

Analysis of induced current density in grounded and ungrounded prolate spheroid models in concurrent ELF electric and magnetic fields

Analyzed in this paper is the induced current density in the homogeneous prolate spheroid model of a biological object exposed to concurrent 60‐Hz vertical electrical field (1 kV/m), and horizontal and vertical magnetic fields (1 to 5 μT) with different phase angle. The analysis has been carried out separately considering the presence of electric and magnetic fields. The current density induced by the electric field is calculated using the finite element method, whereas the current density induced by the magnetic fields is calculated with exact solution for the prolate spheriod model. The total induced current density is the vector sum of the current density components induced by the electric and magnetic fields. It is found that the density of the total current is determined by the vertical electric field and horizontal magnetic field. The horizontal magnetic field has an important effect on the total induced current density distribution. The distribution of the density of the total current varies with the phase difference between the vertical electric and horizontal magnetic fields. As the model gets close to the ground, however, the contribution of the horizontal magnetic field to the total induced current density is found to decrease. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 8–15, 2001