直流耐压试验对电力电缆的影响

对于不同材质的电缆采用卣流耐压试验是否合适,实验结果如何判断,本文作了明确的阐述。直流耐压试验对发现纸绝缘电缆缺陷非常有效,但对交联聚乙烯绝缘电缆存在局限性,不能有效地发现高压交联聚乙烯主绝缘电缆的缺陷。交流耐压试验是检验交联电缆绝缘质量的有效手段。     

面向基因数据分类的旋转森林算法研究

针对基因表达数据高维和小样本的特点,介绍一种基于主成分分析的决策树集成分类算法——旋转森林.首先通过对数据属性集的随机分割,再对子集进行主成分分析变换,保留全部的主成分系数,重新组成一个稀疏矩阵.然后对变换后的数据利用非剪枝决策树集成算法进行分类.再结合ReliefF算法,选用3组基因表达数据验证算法,对比Bagging决策树和随机森林两种集成方法.结果表明旋转森林算法对基因数据具有更好的分类精度,同时验证旋转森林在较低的集成数的情况下,可以取得良好的效果.     

66千伏及以上电力电缆绝缘在线监测系统研究

交联电缆的使用越来越广泛,对其进行在线检测也日趋重要。本文对电缆绝缘进行在线监测方法做了概括介绍,并介绍了一种在不需改变电力系统的原有接线方式便可实现电力电缆绝缘状态的在线测量技术的研究。     

基于决策树和聚类算法的智能电表误差估计与故障检测

针对智能电能表故障检测问题,研究了低压电能系统模型,提出了一种电能表误差估计方法。该方法采用决策树对异常数据进行过滤,并对不同损失水平的数据进行分类,然后对数据进行聚类,得到不同使用行为的数据集。此外,建立了仪表数据矩阵,采用递推算法求解矩阵方程,对仪表误差进行估计。采用递推算法求解方程,并对仪表误差进行估计。最终通过算例验证了所提方法的有效性。     

110kV交联聚乙烯电缆中间接头安装工艺

高压交联聚乙烯电缆中间接头制作是一项技术要求较高、专业知识较强的工作,对安装人员的业务素质、专业知识及技能水平都有较高的要求,电缆加热（校直电缆并防止绝缘回缩）、电缆预处理、绝缘超光处理、应力锥安装、密封处理、金属护套接地安装,每一道环节都非常重要,特别对安装尺寸定位精确度要求非常高。     

电缆绝缘状态及寿命评估

随着城市的发展需求,电缆因其美观安全,受外界气候干扰小,隐蔽,维护工作量少,可在各种场合下敷设等优点,逐渐取代架空裸线,被广泛应用于线路施工中。伴随着城网外扩和农网改造的实施,电力电缆的利用比重也会越来越高,如何维护好已有的和即将投入运行的电缆设备,对电缆的状态监视和寿命评估就显得十分必要。电缆的运行状况直接关系到电力系统的安全运行及供电的可靠性。本文对电缆故障的类型,及绝缘老化的原因做了系统的论述和分析,对电缆绝缘状态检测方法全方位,多角度的进行研究,从而为提高电缆的使用寿命非常具有必要性和实际意义。     

一种基于低压脉冲法的电力电缆故障定位方法

介绍一种基于低压脉冲法的电力电缆故障定位方法,该方法通过检测入射脉冲与反射脉冲的时间差,利用相关计算公式与函数,对测量数据进行相关处理,进而计算出电缆故障距离,并判断电缆的故障类型,并在实际应用中验证该方法的有效性和正确性。     

电力电缆故障测试原理与方法简述

近些年,电力电缆在我国各个电压等级的大量应用,随着而来的是电缆故障越来越多。困扰供电部门的难题就是如何快速、准确的找到电缆故障的精确位置,而其中最重要的就是通过电力电缆故障测试方法测出电缆故障距测试端的距离。本文是对电力电缆故障测试技术进行了描述,文中介绍了电力电缆故障的原因、电缆故障性质的分类和判定,并着重描述了电缆故障测试的几种方法的基本原理与实际应用实例。     

预分支矿物绝缘电缆在隧道照明工程中的应用

随着全国铁路建设的高速发展,铁路隧道工程的重要性与复杂性日益显著。隧道照明工程是隧道施工过程中的重要组成部分,对后期隧道内设备维护具有重要的作用。预分支矿物绝缘电缆作为一种新型电缆,在技术先进性、经济效益性以及安装便利性等方面,相比传统电缆具有突出的优点,被越来越广泛地应用在隧道照明工程中。该文对预分支矿物绝缘电缆的特点进行介绍,着重对其施工注意事项进行分析和探讨,目的在于提高预分支矿物绝缘电缆的施工质量。     

冷水机组故障诊断中重要特征的选择

在数据驱动的集中式空调系统故障诊断过程中,特征选择是一个必要的预处理.选取重要的特征作为分类依据,无论是从经济的角度还是对故障的有效判断上,都具有非常重要的意义.现采用不同的特征选择方法对一组冷水机组故障数据进行特征选取,并利用支持向量机完成分类,最后通过对比分析获取冷水机组故障诊断中最重要的特征子集.     

Testing of the fire-proof functionality of cable insulation under fire conditions via insulation resistance measurements

Two different designs for low-fire-hazard cables were tested under conditions similar to those of the fire test specified in IEC 60331-21. In addition to the other standard requirements, an insulation resistance meter was connected directly to the measurement circuit to monitor the actual state of the cable insulation during the fire tests. The suitability of this measurement of the insulation resistance was demonstrated by testing cables with fire barriers made from mica glass tape and from ceramifiable silicone rubber. The results showed that insulation resistance is sensitively affected by the melting of the organic components of insulation, by the decomposition of the fire retardant, by the ignition of the core insulation and by the formation of a silica layer during a fire test. The results also helped to reveal the importance of flame conductivity in performing such tests. The initial observations are supported by thermogravimetry and differential scanning calorimetry, which are beneficial as a first step towards understanding the mechanisms of fire-proof functionality in cables. The suggested procedure can assist in the comparison of the fire-proof functionalities of different cable designs, in the analysis of their failure mechanisms and in cable design optimisation.     

基于动态故障树的CTCS-3级ATP系统可靠性分析简

 针对传统的可靠性分析方法分析CTCS-3级ATP系统动态失效问题的不足,提出采用动态故障树分析其可靠性。首先,分析系统的结构和功能建立动态故障树模型;其次,采用深度优先最左遍历算法搜索动态故障树模型,得到独立的子树;最后,在引入可修系统可靠性指标基础上,采用解析法和马尔科夫矩阵迭代法求解子树,结合分层迭代方法对动态故障树分析法改进,以减小运算量,使得上述可靠性指标能用于CTCS-3级ATP系统的可靠性评估。计算所得可靠性指标与可靠性框图分析得到的结果对比表明：动态故障树能够更好地描述系统的冗余性和容错性等特点,提高了可靠性指标的精度。     

纳米SiO2对交联聚乙烯交/直流击穿强度和耐电树枝性能影响

为系统地研究纳米SiO₂对交联聚乙烯（XLPE）交/直流击穿强度和交/直流耐电树枝特性的影响,使用平行双螺杆分别制备了含0.5wt%和1wt%纳米SiO₂的纳米SiO₂/XLPE复合材料,以商用直流电缆料和普通XLPE作为参照,测试了掺杂纳米SiO₂对XLPE交流电树枝和直流接地电树枝的引发和生长特性及交/直流击穿强度的影响。实验结果表明,商用直流电缆料的直流击穿强度与普通XLPE相近,但其直流接地电树枝的引发更困难,树枝生长也更缓慢;随着纳米SiO₂添加量增大,纳米SiO₂/XLPE复合材料交/直流击穿强度的作用增强,对交/直流电树枝引发的抑制作用也增强,1wt%纳米SiO₂/XLPE复合材料具有显著抑制直流接地电树枝生长的效果,其直流接地电树枝引发和生长特性均优于商用电缆料;1wt%纳米SiO₂/XLPE复合材料的交流击穿强度和交流电树枝起始电压均高于普通XLPE,但其对交流电树枝的生长抑制作用仅局限在电树枝生长初期,电树枝生长达到一定阶段后,1wt%纳米SiO₂/XLPE复合材料中的电树枝生长速度超过普通XLPE。      

Fractal analysis of side channels for breakdown structures in XLPE cable insulation

The role of frequency in the range 20 through 300 Hz on the breakdown voltage and the breakdown path is studied in cross-linked polyethylene (XLPE) cable insulation using embedded needle. A maximum breakdown voltage of 25 kV is found at 240 Hz, and side channels are observed on the flank of the main channel of the electrical breakdown path. Fractal analysis of the side channel is carried out and it is induced that the frequency dependence of the fractal dimension D of the side channel are similar to that of the electrical trees before breakdown. It is suggested that the space charge can be injected from the needle tip. This leads to partial discharge causing progress of the electrical tree and the breakdown path. Space charge will also result in field-moderating cloud around the needle tip and turn to sidewall charges in the side channels. The frequency dependence of the breakdown voltage of the XLPE with the embedded needle can be clarified based on the fractal analysis of the side channel and the electrical tree of the XLPE insulation.     

Electrical properties of flexible polypropylene based cable insulation materials

DC resistivity and AC breakdown strength of flexible polypropylene (trade marked name Hifax) cable insulation materials have been measured at selected temperatures. The AC breakdown data has been analysed in terms of Weibull distribution. The results show that Hifax cable insulation has a higher AC breakdown strength than EPR (ethylene propylene rubber) and XLPE (crosslinked polyethylene), both of which are widely used for DC cable insulation. It is concluded that blending Hifax with ordinary polypropylene decreases the breakdown strength. The DC resistivity of Hifax is larger than that of XLPE and oil-impregnated paper insulations. It has been found that the electrical stress coefficient of resistivity of Hifax cable insulation increases with temperature, which may have important engineering implications. An anomalous drop in resistivity has been observed for Hifax at high electrical fields, suggesting charge trapping and detrapping processes are present in these cable insulations.     

A fault tree analysis strategy using binary decision diagrams

The use of binary decision diagrams (BDDs) in fault tree analysis provides both an accurate and efficient means of analysing a system. There is a problem, however, with the conversion process of the fault tree to the BDD. The variable ordering scheme chosen for the construction of the BDD has a crucial effect on its resulting size and previous research has failed to identify any scheme that is capable of producing BDDs for all fault trees. This paper proposes an analysis strategy aimed at increasing the likelihood of obtaining a BDD for any given fault tree, by ensuring the associated calculations are as efficient as possible. The method implements simplification techniques, which are applied to the fault tree to obtain a set of ‘minimal’ subtrees, equivalent to the original fault tree structure. BDDs are constructed for each, using ordering schemes most suited to their particular characteristics. Quantitative analysis is performed simultaneously on the set of BDDs to obtain the top event probability, the system unconditional failure intensity and the criticality of the basic events.     

基于改进的判定表的故障树建模方法

针对过程控制系统故障树建模问题提出了一种以步进方式求结构函数的判定表法。采取以事件为条件桩、0和1为条件项的二态判定表的方式,列举各事件所有可能的状态组合,根据每种情况下部件的相互作用演绎输出事件,然后对具有相同输出事件的事件序列求并集以排除重复事件和不相关事件,得到约简的结构函数。通过对硝酸冷却系统建模的验证,用这种方法建树的结果与原文的结果是一致的。     

Field test of liquid nitrogen cooled cryogenic power cable

A liquid nitrogen cooled cryogenic cable, 66 kV, 100 MVA, 30 m was constructed and tested with loads simulating actual operating loads from October 1970 to December 1971. The successful operation of the cable makes us hopeful it can be used for large capacity transmission. Our test line is composed of aluminium stranded hollow conductor, liquid-nitrogen impregnated polyethylene paper electrical insulation, and polyurethane foam thermal insulation.     

A study of breakdown strength of liquid nitrogen cooled power cables

A 66 KV liquid nitrogen cooled cryogenic cable was manufactured and tested using ac and impulse voltages.Liquid nitrogen cooled cryogenic cables will be in practical use over the 275–500 kV range. Study of the 66 kV class cable is the first step towards the development. The insulation system of this cable is polyethylene paper tape wrapped insulation impregnated with liquid nitrogen and its insulation thickness is about 7.75 mm. The influence of bending, conductor surface effect, and thickness dependence on the breakdown strength are discussed.     

纳米TiO2/液体硅橡胶直流电缆附件绝缘复合材料的介电性能

高压直流电缆附件在电力系统运行中,由于复合绝缘电导率不匹配极易导致电场畸变引发绝缘故障。针对这一问题,采用直接共混法制备了不同掺杂浓度的纳米TiO₂/液体硅橡胶（LSR）复合材料,并对其微观形貌和介电性能进行了测试研究。结果表明:纳米TiO₂粒子在LSR基体中分散较均匀,随着TiO₂掺杂含量的增加,纳米TiO₂/LSR复合材料试样的相对介电常数和介质损耗因数增大。当纳米TiO₂粒子添加量为4wt%时,纳米TiO₂/LSR复合材料的电导率与电缆主绝缘交联聚乙烯（XLPE）的电导率近似相等,且随着电场强度的增大,两者的电导率变化趋势也基本一致。电声脉冲法（PEA）测量结果表明,添加4wt% TiO₂的纳米TiO₂/LSR复合材料内积聚的空间电荷最少。纳米TiO₂粒子的掺杂,提高了TiO₂/LSR复合材料电缆附件绝缘电导率对电场强度的响应依赖特性,使其能与XLPE绝缘电导率较好地匹配,同时一定程度地抑制了空间电荷的积累,有助于直流电缆附件内复合绝缘电场的均匀分布。