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     

空间电荷对低密度聚乙烯电气击穿特性的影响

为解决聚乙烯用作电线电缆绝缘材料时所受空间电荷问题的困扰,采用在低密度聚乙烯(low density po-lyethylene,LDPE)试品上施加直流预电压使其中积聚一定量的空间电荷,然后测量试品击穿强度的方法,研究了空间电荷对LDPE击穿特性的影响。结果表明,与未经过预电压处理的LDPE的击穿强度相比,在经过较低场强(50 kV/mm)预电压处理后,预电压与击穿电压极性相同时击穿强度提高了约9%,极性相异时击穿强度降低约14%;而经过较高场强(150 kV/mm)预电压处理后,预电压时LDPE中出现空间电荷包现象,预电压后同极性击穿强度提高约19%,而异极性击穿强度反而上升约16%。分析认为空间电荷包在LDPE中的运动导致了部分空间电荷的中和,使得空间电荷积聚量减少,同时LDPE中可能的缺陷得到了一定程度的老炼而使介质得到了均匀化,从而使LDPE的击穿强度得到了提高。     

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.     

茂金属聚乙烯改善低密度聚乙烯的介电性能

针对高压、超高压直流塑料电缆中存在的空间电荷效应,大多数直流电力电缆常采用改性方法提高其介电性能,如空间电荷特性、体积电阻率和击穿强度等。常用的改性方法主要有添加剂、共混、接枝和二元共聚4种。共混技术较广泛用以改性聚乙烯电缆,提高其介电性能。因此用电声脉冲法(PEA)测量了MPE与LDPE共混试样中的空间电荷分布;用高阻计测量了共混物的体积电阻率,用阶梯电压测量了共混物的交流击穿场强。试验结果表明,1%MPE与LDPE共混能有效降低空间电荷效应,提高交流击穿场强7.9%,略降低体积电阻率。最后讨论了共混物的物质结构、电荷陷阱及介电性能间的关系。     

From LDPE to XLPE: investigating the change of electrical properties. Part I. space charge, conduction and lifetime

This paper discusses the results of space charge, conduction current and electrical lifetime measurements performed on widely-used materials for electrical insulation, that is, low density polyethylene (LDPE) and cross-linked polyethylene (XLPE). Space charge accumulation profiles were compared in LDPE, low density polyethylene plus antioxidant (LDPE+AO) and XLPE, with consideration of thermal treatment effects in LDPE and XLPE. Significant variation (decrease) of accumulated space charge and apparent mobility, as well as slight decrease of conduction current, can be seen going from LDPE to LDPE+AO and XLPE, which may be associated with formation of deeper trap levels (or an increase of their density). On the contrary, electrical life under AC voltage does not show significant differences from LDPE to XLPE. This latter result underlines that life under high AC electrical stress is mostly determined by defects (weak points) rather than material characteristics associated with charge injection and transport.     

Effects of manufacturing technology on electrical breakdown and morphology of thin films of low density polyethylene blended with polypropylene copolymer

Extruded films prepared from blends of low-density polyethylene (LDPE) and random copolymer of ethylene and propylene (EP) with the T-die method were studied with respect to electrical properties and morphology. Comparisons with data on blown films are made. These blends are of interest as improved LDPE for making XLPE for insulated power cable. In the high temperature region (90/spl deg/C), a specimen with a slightly higher EP content had higher impulse breakdown strength than that with a lower EP content, but no improvement of DC breakdown strength by blending could be found. The improvement of impulse breakdown strength (90/spl deg/C) is explained in terms of morphological changes by blending such as the orientation of chains in a film and the size of spherulites on the assumption of the thermal breakdown. In comparison, a T-die film had higher impulse breakdown strength than that of a blown film for the same composition. The impulse breakdown strength also increased with the use of the higher density LDPE. In the current versus electric field characteristics at 30/spl deg/C, the blend polymer with EP content of 5-10% showed a transition from LDPE behavior at low field region to EP behavior at high field region. However, no appreciable difference in current behavior among the specimens was observed at 90/spl deg/C, which suggests an incompatibility between the two materials that exists at 30/spl deg/C but not at 90/spl deg/C.     

取向度对聚乙烯介电性能的影响

聚合物取向度对电气绝缘性能具有重要的影响。该文研究通过两种方法获得具有不同取向度的聚合物材料。在第一种方法中，通过在聚乙烯中加入5％～10％的乙烯．丙烯共聚物使在相同工艺条件下制备的共混物薄膜比纯聚乙烯薄膜具有更高的取向度。在第二种方法中，采用传统的拉伸方法使聚乙烯薄膜的取向度沿拉伸方向得到提高。研究中，多种方法被用于评价薄膜的取向程度，如热收缩率、偏光显微镜和测量声速法等。文中同时研究了具有不同取向度的聚合物薄膜的电气击穿强度，电流和空间电荷特性。分析了聚合物取向度与其电气性能之间的关系，并对其机理进行了探讨。     

DC conduction and electrical breakdown of MgO/LDPE nanocomposite

To understand basic electric properties of nano-sized magnesium oxide (MgO) / low-density polyethylene (LDPE) nanocomposite under DC voltage application, the volume resistivity, the space charge distribution and the breakdown strength were investigated. By the addition of nano-sized MgO filler, both the DC breakdown strength and the volume resistivity of LDPE increased. At the average DC electric field of about 85 kV/mm and more, a positive packet space charge was observed in LDPE without MgO nano-filler, whereas a little homogeneous space charge was observed in MgO/LDPE nanocomposite material at the front of electrode. From these results, it is confirmed that the addition of MgO nano-filler leads to the improvement of DC electrical insulating properties of LDPE.     

The effect of nano‐ZnO on corona aging and photo aging in low‐density polyethylene

In this paper, space charge distributions as well as dielectric properties, such as volume resistivity and AC breakdown strength, were studied in low‐density polyethylene (LDPE) and its composite obtained by adding nano‐ZnO nanofiller, before and after photo‐oxidation or corona aging for several days. It was found that a small amount of ZnO nanoparticles could effectively improve both the photostabilization and corona stabilization of the LDPE matrix. Fourier transform infrared (FTIR) spectra of the specimens were investigated to reveal the change of the microstructures. The results showed that a weaker carbonyl absorption peak appeared in LDPE/ZnO nanocomposite than in LDPE. A proper explanation is given according to the photodegradation and corona degradation theory of polyethylene. The results also showed that there was a certain similarity between photo aging and corona aging. IEEJ Trans 2010 DOI: 10.1002/tee.20600     

Space charge formation and breakdown in polyethylene influenced by the interface with semiconducting electrodes

This paper deals with the influence of interface between polyethylene and semiconducting electrode on the space charge formation and electrical breakdown. Low‐density polyethylene (LDPE) films attached with different semiconducting electrodes were subjected to the DC breakdown test, and corresponding space charge distribution was measured. A heat treatment to LDPE itself did not bring about a significant change in space charge profile; however, when a semiconducting electrode was hot‐pressed, the impurities would migrate into LDPE at high temperature, leading to the change in space charge profile. Furthermore, it was suggested from the comparison between the results with degassed and as‐received semiconducting electrodes that some carriers relating to impurities in the electrode would move into LDPE under the voltage. In addition, it was shown that the breakdown is not determined by the field at the cathode which can supply sufficient electrons, but by the maximum field across the specimen, suggesting that an increase in conduction current due to the generation and/or injection, rather than the electronic avalanche process, leads to the breakdown. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 19–25, 2002     

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     

茂金属聚乙烯改性低密度聚乙烯介电性能与机械强度

为提高聚乙烯电缆料的击穿强度和机械性能,将少量茂金属聚乙烯(MPE)与普通低密度聚乙烯(LDPE)共混,用电声脉冲法(PEA)测量直流预压短路后的残余空间电荷量;详细研究了共混物的体积电阻率、直流击穿强度、直流预压反极性击穿电压和机械强度.实验结果表明:当MPE含量为1wt%时,能有效提高共混物的击穿强度和机械强度,但同时降低了体积电阻率和材料韧性,而且聚乙烯的介电性能和机械强度与其结晶形态密切相关.     

用等温电流法研究自由基清除剂的作用机理--聚合物电老化陷阱理论的实验验证

首先对含有自由基清除剂以及纯聚乙烯的薄膜试样进行了准均匀电场下的电老化试验 ,发现自由基清除剂能够提高均匀电场下聚乙烯的电老化寿命。对老化试样进行等温电流衰减试验 ,测得其中的陷阱能级分布 ,结果表明作为浅陷阱存在于试样中的自由基清除剂 ,能够有效地减少电老化过程中深陷阱的产生 ,从一个侧面验证了聚合物电老化的陷阱理论。     

The effect of low-molecular-weight species on space charge andconduction in LDPE

We have investigated the effect of low-molecular mass species on the space charge behavior such as space charge distribution and electrical conduction of LDPE (low density polyethylene). We also attempted to explain the relationship between the space charge distribution and electrical conduction. The heterocharge, conduction current and effective charge mobility decreased when the low-molecular-mass species in LDPE was removed. It was found that the decrease in conduction current was related to the decrease of heterocharge in 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。     

纳米SiO2/低密度聚乙烯复合介质的击穿特性

聚合物纳米复合介质的击穿强度与纳米填充颗粒的质量分数、粒径和表面处理密切相关。以不同表面处理的纳米SiO2颗粒为填料,制备了不同填充质量分数、粒径的纳米SiO2/低密度聚乙烯(low density polyethylene,LDPE)复合介质,测试了其在交流、直流正极性和直流负极性3种不同类型电场下的击穿场强。结果表明:在所研究范围内,填充纳米SiO2颗粒可以提高低密度聚乙烯的击穿场强,并且随着填充质量分数的增加,复合介质的击穿场强有升高的趋势。纳米颗粒填充质量分数相同时,在12~16 nm粒径下,复合介质的击穿场强有随纳米SiO2粒径的升高而降低的趋势;在7 nm小粒径下,可能由于纳米颗粒容易团聚,导致击穿场强较粒径大时要低。另外,纳米SiO2颗粒表面经疏水性处理后,能够有效提高复合介质的击穿场强。     

The application of novel polypropylene to the insulation of electric power cable (3)

Having a higher melting temperature than polyethylene, polypropylene has been expected to be an insulation material for power cables. But isotactic polypropylene (i‐PP) used generally is unsuitable as cable insulation because it shows poor flexibility, low breakdown strength due to growing spherulites, and so on. But stereoregular syndiotactic polypropylene (s‐PP) newly developed with metallocene catalyst shows quite different properties than i‐PP. In our previous paper, we investigated the basic properties of s‐PP and the initial properties as a cable which was manufactured using s‐PP insulation. It was revealed that s‐PP had superior thermal and electrical properties to cross‐linked polyethylene and the s‐PP insulation table showed satisfactory initial properties. However, in order to apply to an actual cable, the properties must be maintainable over 30 years after construction. In this paper, we estimated the long‐term remaining properties for s‐PP insulation table. A series of experiments on long‐term properties gave the following results: (1) s‐PP cable shows longer life over 30 years; (2) the breakdown strength of s‐PP cable after a long‐term experiment equal to 30 years is slightly lower than the initial breakdown strength, but it is sufficient as a remaining property. Furthermore, water‐tree resistivity of s‐PP was investigated and it was revealed that s‐PP significantly suppressed the water tree propagation compared with XLPE. These results suggested that s‐PP cable would serve as a next‐generation cable. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 1–8, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20114     

Effects of sample preparation conditions and short chains on spacecharge formation in LDPE

The effects of chemical change during sample preparation and low molecular weight chains of low density polyethylene (LDPE) have been investigated in order to clarify the origins for heterocharge in LDPE which does not contain antioxidants. The carbonyls formed at the surface of polyethylene (PE) sheet prepared at 180°C with polyethylene terephthalate backing films were found to contribute to the increase of heterocharge in LDPE. All aspects of the processes used for the preparation of samples must be studied carefully to ascertain possible effects on the properties of samples. The type of charge accumulated in LDPE was also found to depend on the concentration of short PE chains. Details of experimental results and their possible causes are described     

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。     

蒙脱土改性聚乙烯复合材料的高场介电性能研究

利用熔融插层法制备了聚乙烯/蒙脱土纳米复合材料,研究蒙脱土对聚乙烯介电性能的影响。研究分析了纯聚乙烯和不同的聚乙烯/蒙脱土复合材料的树枝化性能,通过直流预电应力电树引发试验,探讨了空间电荷的极性效应对不同材料树枝化性能的影响。试验结果表明:与纯聚乙烯和其他复合材料相比,加入相容剂的聚乙烯/蒙脱土纳米复合材料的电树潜伏期更长,电树生长速度更慢,而且显示出与LDPE不同的极性效应。不同材料的热激电流(TSC)试验结果显示:聚乙烯/蒙脱土纳米复合材料的松弛时间分布展宽,峰值增高,说明在纳米复合材料中引入了更多的陷阱能级,这些陷阱调制了载流子浓度和迁移率,从而抑制了树枝的起始与生长。