Gradient Changing Morphology Research of Cross-linked Polyethylene Thick Insulation of 110 kV Power Cable

The thick insulation layer of 110 kV XLPE power cables will result in the gradient changing morphology with the radius due to crosslinking process and cooling of the XLPE insulation. In this paper, the morphology of cross-linked polyethylene （XLPE） insulation of 110 kV cable and the uniforming effect of the heating process on it are researched by the differential scanning calorimetry （DSC） and X-ray diffraction （WAXD）. The middle layer morphology structures of insulation produced by normal technology are of better uniform, while the crystallinity of the inner and outer layer of the insulation is lower than that of the middle one. The melting enthalpy AHm of materials displays the difference of the crystal morphologies sensitively. The difference of crystallizing morphology in different layers of the high-voltage power cable insulation can be improved by heating process. But the uniforming of morphology of the insulation by heating process requires sufficient ttanperature and time. The effect of the on-line stress-relaxation equipment used widely by cable works now should be doubted. The test results of WAXD reveal that thermal stress changes the interplanar distances in the crystal region. So the radical stress in the insulation is tensile mainly.

Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature. Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method. Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes. In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time. And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test. As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking. From the results of the 1H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution. Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.

Reattachment of the Osteotomized Greater Trochanter in Hip Surgery Using an Ultrahigh Molecular Weight Polyethylene Fiber Cable: A Multi-Institutional Study

The purpose of this multicenter study was to evaluate the clinical performance of an ultrahigh molecular weight polyethylene (UHMWPE) fiber cable for re-attachment of the osteotomized greater trochanter in hip surgery. Included in the study were 85 hips that had undergone surgery with greater trochanter osteotomy, including 50 hip arthroplasty procedures and 35 hip osteotomies. The osteotomized greater trochanter was reattached using one or more UHMWPE fiber cables. The bone union and displacement of the greater trochanter were assessed in radiographs for up to 12 months after surgery. Non-union of the osteotomy site occurred in 4.7% of the cases. In approximately 90% of the cases, displacement was less than 2 mm at up to 12 months after surgery. The UHMWPE fiber cable was a good biomaterial for reattaching the osteotomized greater trochanter and may also be an option for osteosynthesis procedures.

Highly cross-linked versus conventional polyethylene inserts in total hip arthroplasty,a five-year Roentgen stereophotogrammetric analysis randomised controlled trial

BACKGROUND Polyethylene(PE)particles produced by wear of the acetabular insert are thought to cause osteolysis and thereby aseptic loosening of the implant in total hip arthroplasty(THA).As highly cross-linked polyethylene(HXLPE)is presumed to give lower wear rates,in vivo studies are needed to confirm this.AIM To compare the wear of REXPOL,a HXPLE,with conventional PE within the first five years after implantation using Roentgen stereophotogrammetric analysis(RSA).METHODS Patients were randomised to receive either a HXLPE(REXPOL)or a conventional PE insert during primary THA.RSA images were obtained directly postoperative and after 6 wk,12 wk,6 mo,12 mo,24 mo and five years.Functional outcomes were assessed using the Hip Injury and Osteoarthritis Outcome Score and Harris Hip Score at baseline and five years after surgery.RESULTS The HXLPE(REXPOL)showed less wear in the latero-medial direction.Significant wear rates of conventional PE were seen in the latero-medial and center-proximal direction and in volume and corrected volume,whereas the REXPOL did not show these outcomes over time.Improvement from baseline in functional outcome did not significantly differ.CONCLUSION Total 3D wear is less in THAs inserted with a REXPOL inlay than a conventional PE inlay after five years.This study confirms,for the first,that the REXPOL HXLPE inlay is preferred to standard PE.

Preparation of Controllable Cross-Linking Polyethylene Foaming Materials and Their Properties

In order to prepare the polyethylene materials with controlling properties,we developed two kinds of controllable cross-linking polyethylene foaming system.2,5-dimethyl-2,5-bis (tert-butyl peroxy) hexane was used as cross-linking agent and TEMPO as cross-linking inhibitor,azodicarbonamide (AC) was used as foaming agent and citric acid as foaming promoter.The density,expansion ratio,cellular structure and mechanical property of these two kinds of controllable materials were studied.Experimental results show that,properties of these two kinds of materials appear similar trend:cellular size and expansion ratio are enlarged with the amount of cross-linking inhibitor or foaming promoter increasing,while density and mechanical strength appear decreasing trend.Through comparing those two material systems’ properties,cross-linking polyethelene foaming system with citric acid as foaming promoter has better properties.

RECENT DEVELOPMENTS IN PHOTOINITIATED CROSSLINKING OF POLYETHYLENE AND ITS INDUSTRIAL APPLICATIONS

The recent developments in the photoinitiated cross-linking of polyethylene and the significant breakthrough of its industrial application are reviewed. The enhanced photo-initiation system, the dynamics of photoinitiated crosslinking, the optimum conditions, the crystal morphological structures and related properties, and the photo- and thermo-oxidation stability of photocrosslinked polyethylene (XLPE) materials have been elucidated systematically. A new technique for producing photocrosslinked XLPE-insulated wire and cable is described in detail. It can be expected that the future applications of photocrosslinking technique of polyolefins will be very promising.

MODIFICATION OF POLYETHYLENE BY in situ FORMED SODIUM ACRYLATE

To improve the water tree resistance of PE, linear low-density polyethylene （LLDPE） was compounded with sodium acrylate （NaAA） for in situ polymerization, in which NaAA was fbrmed through the neutralization of acrylic acid （AA） with sodium hydroxide （NaOH） before adding dicumyl peroxide （DCP） to initiate the in situ graft polymerization and homo polymerization. A series of LLDPE/NaAA compounds were investigated for their water absorption ratio （WAR） measurement, water treeing, mechanical and dielectric properties. The results strongly suggest that NaAA can improve the water tree resistance of LLDPE. In addition, the LLDPE/NaAA compounds possess satisfactory mechanical properties and dielectric properties. Characterization of LLDPE/NaAA compounds by using Fourier transform infrared spectrometry （FTIR） suggests that the neutralization and polymerization reaction could be achieved effectively. Using adequate DCP content is the key factor for controlling the polymerization of NaAA with precise conversion ratio.

A Cross-linked Polyethylene with Recyclability and Mechanical Robustness Enabled by Establishment of Multiple Hydrogen Bonds Network via Reactive Melt Blending

Physical cross-linking by hydrogen-bonds (H-bonds), providing a good combination of application properties of thermosets and processability of thermoplastics, is a potential strategy to resolve the recycling problem of traditional chemically cross-linked polyethylene. However, ureidopyrimidone (UPy), the most widely used H-bonding motif, is unfavorable for large-scale industrial application due to its poor thermal stability. In this work, H-bonds cross-linked polyethylene was successfully prepared by reactive melt blending maleic anhydride grafted polyethylene (PE-g-MAH) with 3-amino-1,2,4-triazole (ATA) to form amide triazole ring-carboxylic acid units. Triazole ring can easily generate multiple H-bonds with carboxylic acid and amide. More importantly, these units are more thermal stable than UPy due to the absence of unstable urea group of UPy. The introduction of H-bonds cross-linking leads to an obvious improvement in mechanical properties and creep resistance and a good maintain in thermal properties and recyclability. Furthermore, the reinforcement effect monotonically improves with increasing the density of H-bonds. The obtained good properties are mainly attributed to largely enhanced interchain interactions induced by H-bonds cross-linking and intrinsic reversibility of H-bonds. This work develops a novel way for the simple fabrication of H-bonds cross-linked PE with high performance through reactive melt blending.

Studies on the Effect of Accelerated Thermal Aging on Electrical and Physicochemical Properties of XLPE Cable

The degradation of crosslinked polyethylene (XLPE) cable insulation during service, such as thermo-oxidation and water treeing may lead to a premature electrical breakdown of the XLPE insulation cables. Therefore, it is necessary to optimize the period of replacement to evenly distribute the replacement cost by ascertaining the deterioration degree. Estimation of the aging degree is at present the most important task for diagnosis of the residual lifetime of the power cable insulation. This paper presents a study on the changes in the dielectric properties of the thermally aged XLPE cables in the frequency range from 0.07～10 MHz. Based on electrical and physicochemical characterization, some new "dactylograms" for the thermally aged XLPE cable insulation have been proposed.

Partial Discharge Simulations Used for the Design of a Non-Intrusive Cable Condition Monitoring Technique

The purpose of this paper is to investigate the effect of PD （partial discharge） activity within medium voltage XLPE （cross-linked polyethylene） cables. The effect of partial discharge was studied by means of a number of simulations. The simulations were based on the well-known three capacitor model for partial discharge. An equivalent circuit was derived for partial discharge due to a single void in the insulation material of a power cable. The results obtained from the simulations will form the basis of the design proses of a non-intrusive condition monitoring technique. The technique is based on the classification of discharge activity according to five levels of PD. Future work will include the improvement of the simulation model by investigating the high frequency model of a power cable as well as the statistical nature of PD activity. This will improve the accuracy of the simulation results when compared to actual measurements. The work discussed in this paper will be used to construct and calibrate a practical model which will make use of PD measurements for non-intrusive condition monitoring of medium voltage electrical cables.

高压XLPE电缆缓冲层缺陷研究现状综述

高压交联聚乙烯电缆因缓冲层缺陷引发的故障频发,已严重威胁到电力系统的安全运行。本文首先介绍了缓冲层的基本结构和作用,并在此基础上梳理了目前国内外对于缓冲层失效的相关研究;其次从缓冲层的材料特征和内部结构等角度结合电场仿真来分析缺陷发生的主要原因;之后对缓冲层缺陷中出现的白色粉末绝缘性能和理化特征进行总结,并提出其形成机理;最后对缓冲层缺陷的检测手段进行汇总,提出使用计算机断层成像技术对电缆缓冲层缺陷进行检测以弥补现有检测手段的不足,并建议对铝护套及缓冲层的材料或结构进行优化,以预防缓冲层缺陷的生成。

高压电缆用交联聚乙烯绝缘材料

聚乙烯材料具有优良的介电性,其作为高压电缆绝缘材料的应用愈加广泛。但交联聚乙烯的导电性会随着电荷积聚以及温度梯度出现明显的变化,影响绝缘材料性能的发挥。本文综合分析了交联聚乙烯材料在高压电缆中的研究重点,希望能够为未来交联聚乙烯下料的进一步改性提供参考。

基于修正分数Poynting-Thomson模型的高压XLPE海缆绝缘评估

为利用频域介电谱准确评估高压交联聚乙烯(XLPE)海缆的绝缘状态,建立考虑直流电导率的修正分数Poynting-Thomson模型(分数P-T模型)以解析高压XLPE海缆的介电特性。首先,通过加速老化试验制备不同老化程度的高压XLPE海缆试样,并测得各组老化试样的力学、理化和介电数据。然后,应用修正分数P-T模型对实测介电曲线进行拟合,对比修正前后分数P-T模型表征实测介电曲线的效果。最后,通过仿真探究模型参数对介电曲线的影响规律,构建模型参数与绝缘程度之间的联系,将提出的老化特征参数与断裂伸长率(EAB)进行量化研究。研究结果表明,修正分数P-T模型能够准确拟合出不同老化程度高压XLPE海缆试样的介电曲线,提出的老化特征参数α、ε_(a)、ε_(b)和σ_(dc)可实现对高压XLPE海缆绝缘状态的量化评估。

低密度聚乙烯基料链结构对黏弹特性的影响

高压电缆向高电压等级和大长度的发展,对交联聚乙烯绝缘料的加工性能提出了更高的要求。绝缘料的加工性能和电缆绝缘成型质量主要受低密度聚乙烯(LDPE)基料黏弹特性影响,基料的黏弹特性取决于其链结构。然而,由于LDPE基料分子链支化结构复杂,难以建立单一的链结构参数与黏弹特性的关联,因此精准地获得LDPE链结构特征对黏弹特性的影响对电缆绝缘优化升级至关重要。该文采用制备型升温淋洗分级工艺,对管式法LDPE和釜式法LDPE进行分级得到具有不同平均分子量的级份,采用凝胶渗透色谱法和旋转流变仪表征原料和级份的链结构参数及黏弹特性。结果表明,长链支化结构相似时,重均分子量越大,分子链间越容易产生缠结,黏度和模量越高,剪切变稀现象发生频率越低;重均分子量接近时,零切黏度与长链支化度具有非单调关系,过高的长链支化度会削弱分子链间的物理缠结,导致零切黏度降低。基于LDPE黏弹特性构效关系,结合电缆挤出成型工艺,设计更为适宜的基料黏弹特性参数,以此优化调控LDPE的链结构,是未来高端电缆绝缘材料研发的方向。

黑曲霉菌对废旧电缆聚乙烯降解效果及反应机理研究

近年来,随着电缆批量退役,有机固体废物大量堆积,严重威胁环境清洁和人类生命健康。微生物降解废旧电缆比传统的焚烧填埋更为清洁、经济,因此可以采用菌群降解手段实现废旧电缆环保处理。为了研究微生物降解废弃聚乙烯(PE)组分的过程,该文选取黑曲霉菌对聚乙烯粉末进行降解处理,利用傅里叶红外光谱(FTIR)和X射线光电子能谱(XPS)进行官能团分析及样品表面碳、氧元素的含量分析,使用X射线衍射实验(XRD)进行样品的晶体结构分析,采用差示扫描量热-热重分析(DSC-TGA)联用热分析方法开展样品的变温热性能分析,同时基于扫描电子显微镜(SEM)进行10 000~50 000倍下样品的微观形貌观测。实验结果表明,在黑曲霉菌降解低密度聚乙烯的过程中发生了氧化反应,产生了羟基、羰基等亲水基团,在菌群处理聚乙烯天数为14天时,氧元素含量从1.38%增加至13.60%,同时聚乙烯结晶度从53.4%下降到34.18%,起始热解温度降低200℃,最终热解温度降低10℃,熔融峰降低0.87 mW/mg,表面形貌出现明显的孔隙和沟壑。该文解析了黑曲霉菌降解低密度聚乙烯的化学机制为醇化、羰基化以及酶促氧化反应。

熔融状态下聚乙烯电缆料老化行为的研究

在200℃的老化温度下,分别采用静态和动态热老化试验方法研究了熔融状态下聚乙烯(PE)电缆料的老化行为。分析了熔融状态及老化时间对PE材料结构、拉伸性能和介电性能的影响。结果表明,静态老化以材料表面氧化为主并表现出较高的表面羰基指数;动态老化材料氧化均匀并伴有大分子主链的断裂,其羰基指数显著低于静态老化样品的表面羰基指数;老化后样品的断裂伸长率随老化时间的增加而显著降低,介电常数和电导率表现出随老化时间增加而增加的趋势。动态老化过程使得材料力学性能失效提前,介电常数增加显著,可用于快速评价PE电缆料的老化行为。

高压电缆交联聚乙烯绝缘料黏度参数对挤出特性影响的仿真研究

高压电缆交联聚乙烯(XLPE)绝缘料及其挤出成型技术是我国高压电缆生产的关键问题。绝缘料的黏度参数会影响其在单螺杆挤出机内包括挤出口流率和流道内熔体最高温度等的挤出特性,进而决定了高压电缆绝缘的成型质量和绝缘性能。该文通过仿真模拟的方法研究了高压电缆交联聚乙烯绝缘料的黏度参数对挤出特性的影响,提出利用绝缘料挤出最高温度-挤出口流率曲线反映不同黏度参数下的挤出特性变化规律。结果表明,最高温度随着挤出口流率增大而升高,零切黏度和松弛时间对最高温度-挤出口流率曲线的斜率影响最大,幂律指数次之,温度系数影响最小。其中,零切黏度和幂律指数与挤出口流率和最高温度的关系均为正相关,且零切黏度增大到一定值后挤出口流率不再明显增大而最高温度持续提升;松弛时间和温度系数与挤出口流率和最高温度的关系均为负相关,且温度系数较小挤出特性较好。最终,根据实际电缆绝缘料挤出生产需求,提出了绝缘料黏度参数的适宜范围。该文可为国产高压电缆交联聚乙烯绝缘料的研发和挤出成型技术的提升提供重要数据支撑与理论依据。

交联聚乙烯绝缘料耐焦烧性能的对比研究

选取3种牌号商用高压电缆交联聚乙烯绝缘料为研究对象,首先通过高温剪切作用下绝缘料熔体扭矩随温度的变化规律,对比分析3种绝缘料的耐焦烧性能,并通过凝胶含量表征焦烧试样的焦烧程度,然后提出采用绝缘料熔体在高温下的扭矩变化率作为特征量来表征绝缘料耐焦烧性能的方法,并通过不同牌号商用绝缘料焦烧程度的表征结果验证该方法的有效性。此外,通过红外光谱对3种绝缘料中交联剂含量和抗氧剂含量进行对比分析,结合凝胶渗透色谱法测得的绝缘料基料分子量,建立了绝缘料添加剂含量、基料分子量与其耐焦烧性能的关联。结果表明:通过绝缘料在高温剪切作用下的扭矩分析,可以有效区分不同商用绝缘料的耐焦烧性能,并发现交联剂含量过高是导致绝缘料耐焦烧性能差的主要原因,通过适当减少交联剂用量、增加抗氧剂用量、降低重均分子量可以提升绝缘料的耐焦烧性能。

不同热老化温度下高压电缆绝缘特性及失效机理

高压电缆的运行温度是影响其绝缘性能的关键因素。该文通过对交联聚乙烯(XLPE)开展不同温度下的加速热老化实验,对比了XLPE微观理化性能和宏观电学性能的变化规律。同时,在微观层面模拟了XLPE分子在不同温度下自由体积与均方位移的变化规律,在宏观层面结合XLPE的介电性能分析了高压电缆内部温度场的变化规律,进而揭示了高温下高压电缆的绝缘失效机理。研究结果表明,随着老化温度的升高,XLPE分子的劣化程度加快,羰基、碳碳双键等官能团含量增大;介质损耗因数与介电常数逐渐增加,甚至出现了突增的现象;结晶区结构的被破坏加快了击穿场强的下降;分子运动加剧,自由体积率从12.53%增大至14.07%。老化后介电性能的下降会导致电缆内部温度升高,从而对电缆的热老化起到了正反馈作用。

不同温度及厚度下非交联聚乙烯电缆绝缘材料工频交流击穿表现

热塑性聚乙烯基电缆绝缘材料具有优于交联聚乙烯(cross-linked polyethylene,XLPE)的电气和机械性能,有望成为新一代绿色环保的电缆绝缘材料。在电缆结构设计中,保守的安全绝缘厚度使得电缆的生产成本增加,降低绝缘层的击穿电场强度;并且在电缆实际运行过程中,绝缘材料往往工作在70~90℃高温环境下;因此针对新型绝缘材料,温度及厚度对其击穿电场强度的影响研究具有工程实际意义。以线性低密度聚乙烯(linear low density polyethylene,LLDPE)/高密度聚乙烯(high density polyethylene,HDPE)共混绝缘材料为研究对象,进行不同温度下(30、70、90、105℃)及不同厚度下的工频击穿实验,研究温度和厚度对其交流击穿的影响。测试结果表明:相较于XLPE绝缘材料,70L-30H(即LLDPE与HDPE在配比为7∶3的情况下熔融共混得到的绝缘材料)具有较高的工频击穿电场强度,在低于工况温度环境下,其击穿电场强度的温度稳定性较高;然而70L-30H的工频击穿电场强度受厚度影响程度略高,但在相同厚度下其击穿电场强度仍明显高于XLPE。上述研究可为热塑性聚乙烯基电缆绝缘材料研发提供参考。