电力电缆局部放电特征分析及运维检修策略研究

电力电缆局部放电检测是检测电缆绝缘状态的重要故障检测方法。然而,目前对于XLPE直流电缆局部放电的特征与分析相对空白,因此研究XLPE直流电缆局部放电的现象与特征,有助于对XLPE高压直流电缆绝缘状况的有效评估,同时对高压电缆的故障诊断与运维检修工作有着重要意义。首先使用Comsol仿真软件对XLPE电缆中间接头进行了仿真,分析了不同缺陷情况对XLPE电缆的影响;随后对不同类型的电缆绝缘缺陷进行了模拟试验,总结了XLPE直流电缆局部放电过程中的各类现象和特征,提出了XLPE电缆运维与检修工作的参考策略。     

交联聚乙烯电缆局部放电的在线检测

针对交联聚乙烯(XLPE)电缆局部放电在线检测存在的问题,结合国内外电缆局部放电在线检测方法的研究和应用情况,进行分析和比较,提出了XLPE电缆局部放电在线检测方法.分析结果表明:对XLPE电缆的局部放电进行在线检测是及时发现故障隐患,预测运行寿命,保障电力电缆安全可靠运行的重要手段.     

高压交联聚乙烯电缆绝缘老化及其诊断技术述评

对国内外部分高压交联聚乙烯(XLPE)电缆系统的绝缘损坏作了统计，分析了电缆及其附件绝缘老化原因和形态，叙述了XLPE电缆绝缘老化的机理。指出对高压电缆附件和缺乏径向防水构造的XLPE电缆需重视绝缘老化问题。对于XLPE电缆本体绝缘老化检测，认为高压级可比中压级简化。概述了国外绝缘老化诊断新技术的发展。最后，对局部放电检测绝缘老化技术方法作了试验探讨。     

基于脉冲电压法的XLPE电缆水树劣化诊断研究

本文提出了基于脉冲电压法的XLPE电缆水树劣化诊断方法,并采用脉宽为1～10 ms的高压脉冲对人工水树劣化XLPE电缆及6.6 kV自然劣化XLPE电缆进行检测和验证。结果表明:采用脉冲电压法成功检测到了与水树劣化有关的电流信号,脉冲电压的平均效应提高了与水树相关的信号的检测灵敏度,但是该方法对自然水树劣化电缆的测试结果与传统方法存在差异,这可能与水树的类型、形态及深度等有关。     

用电磁波速诊断XLPE电缆绝缘

XLPE电缆绝缘诊断的研究对于掌握电缆的绝缘老化状态,保证电力传输系统的安全可靠运行有着十分重要的意义。针对工程实际中大规模应用的诊断方法不多见的现状,提出了一种XLPE电缆状态检测的新方法,即用电磁波在一段XLPE电缆中的传播速度作为诊断这段电缆是否发生老化的依据。在阐明了该方法的原理和理论依据后介绍了所搭建的实验平...     

多传感器联合检测技术在XLPE电缆附件局部放电定位中的试验研究

介绍了目前常用于XLPE电缆局部放电检测中的高频电流法、超高频法和声发射法检测原理,并在此基础上提出了多传感联合检测技术用于XLPE电缆附件局部放电定位的方法。通过在XLPE电缆中人工模拟局部放电信号的方式,进行了多传感器的联合定位试验。试验研究结果表明,多传感器联合检测技术在XLPE电缆附件的局部放电检测和定位中具有很好的有效性和实用性。多传感器的联合应用可以有效地排除现场干扰,提高局部放电检测与定位结果的可靠性。     

便携式XLPE电缆绝缘检测装置

介绍一种便携式XLPE电缆绝缘检测装置。该装置综合运用了电磁耦合法、超高频法和超声波法来检测电缆的局部放电信号。通过分析局部放电信号,并结合电缆温度,判断XLPE电缆的绝缘状况。     

XLPE电缆局部放电在线监测系统的研制

局部放电检测是判断XLPE电力电缆绝缘状况的重要手段。设计并开发了一套用于中压XLPE电缆的局部放电在线监测系统,详细阐述了其工作原理、硬件组成、软件设计及实现方案。通过监测XLPE电缆屏蔽层接地线中的高频电流信号,来分析评估XLPE电缆的绝缘状况。现场运行结果显示,系统稳定可靠,能满足整个变电站中压XLPE电缆绝缘监测的需要。     

交联聚乙烯电缆附件局部放电的联合检测方法研究

随着交联聚乙烯（XLPE）电缆线路的增多和投运时间的逐年增长,各类问题逐渐凸显,尤其是电缆附件的绝缘事故不断增多,而局部放电是评价XLPE电缆绝缘状况的重要指标,也是诊断电缆故障的有效方法。简要介绍当今常用的2种电缆局部放电在线监测方法,即电容差分法和特高频法（UHF）,重点介绍了它们的联合检测,利用差分传感器解决局部放电标定问题,利用UHF特高频传感器进行抗干扰处理。运用联合检测方法对现场运行的XLPE电缆进行了局部放电在线监测,取得了良好的效果。     

XLPE电缆附件局部放电UHF和VHF联合检测

介绍了电磁耦合法测量XLPE电缆局部放电故障原理以及应用方法,重点比较了基于VHF（甚高频）传感器和UHF（特高频）传感器的检测方法在XLPE电缆局部放电在线监测技术中的应用。结合2种检测方法各自的优点与存在的弊病(VHF:衰减慢,可标定放电量,抗干扰能力差;UHF:抗干扰能力强,衰减快,不可标定放电量),推荐了XLPE电缆附件局部放电的UHF和VHF联合检测方法。     

An improved charge-sharing elimination pseudo-domino logic

In low-power digital circuit, the deviation of node voltage from nominal value due to charge-sharing leads to erroneous output. This problem is more prominent in domino logic when the device is scaled down. The scaling of the device involves scaling of threshold voltage, resulting in high leakage, less robustness and degradation in noise margin. The paper proposes an improved domino approach in terms of reduced leakage, low power dissipation and better noise margin. The stacking effect and pseudo buffer are used in precharge phase to control the gate-to-source voltage of pull-down network for less power consumption and increase in performance in terms of speed of operation. A modified keeper is introduced to reduce the charge-sharing problem. The proposed domino approach is tested against area overhead, ageing and process, voltage and temperature variation. The circuit is simulated using Cadence Virtuoso Spectre for 90 nm technology. The results obtained from the simulation represent the usefulness of the proposed circuit in terms of power dissipation, stability due to temperature variation, leakage due to temperature variation and delay. The result also shows that the circuit is less prone to charge redistribution problem that exist in domino circuit.     

无源与有源结合电力滤波器阻尼谐波振荡的重复学习Boost变换控制

提出了一种基于恒频Boost变换技术的PWM逆变器重复学习控制策略.该控制策略中,逆变器被视为Boost变换器实现谐波域内单位功率因数整流控制的同时,重复迭代学习策略由每个学习周期内Boost变换控制所产生的系统谐波电流获取被补偿谐波电压源的模型知识,从而形成PWM逆变器参考电压.以负载为晶闸管整流器的工业电力系统为例,验证了无源与有源结合的混合滤波器应用该控制策略的补偿效果.仿真结果表明,该控制器具有高稳定性、强鲁棒性、低稳态误差、快速跟踪等特点,抑制谐波振荡非常有效.     

Failures in outdoor insulation caused by bird excrement

The bird excrement, combined with humidity, causes line outages in transmission lines. In order to standardize the criteria to solve the problem, a research project was developed in México. The solutions found in worldwide review can be classified into four groups: elimination of birds, devices of dissuasion, physical barriers, and covering devices. The first group includes all bird elimination techniques. These alternatives are forbidden in México, and in most of the countries. The second group has shown to be effective at the beginning of its application; however once the birds are habituated to the device, it loses its effectiveness. The efficiency of the third group, the use of physical barriers, is high, as demonstrated by more than a few review reports informing drastic reductions of flashovers on the transmission lines where they have been installed. The fourth group is conformed by components whose function is to protect or to cover the insulation. According to the experience in Mexico, covering devices have shown to be very effective. The contamination by bird excrement has not a unique solution. The most viable solution is a combination of alternatives. Even though, a solution adopted for a region may not be suitable for another region. Therefore, each case should be approached according to the particular conditions of the region.     

Generalized probability density function and applications to the experimental data in electrical circuits and systems

The mathematical sciences, and particularly probabilistic and statistical methods, are key to understanding the dependencies of the systems. The purpose of this paper is to encourage a wider recognition by engineers of a new generalized principle which in its mathematical form is a powerful instrument for the solution of practical problems. Generalized probability density function was introduced to permit analysis without pre-knowledge of the source of the data. The fundamental principles are extended to apply the most related engineering applications without the need to know the type of source generating the data. The generalized model presented eliminates preliminary work in engineering problems. The proposed model introduces an exponential density function to produce a direct solution to randomly varying data. The exponential density function is fully compatible with applications containing randomly distributed data. The success of the generalized model presented is due to the calculated parameters in the exponential density function. The method is applied to various problems chosen from the field of engineering with great success.     

水平分层土壤中矩形混凝土任意形状复合接地网电阻的计算

对水平分层的多层土壤，先使用等效电阻率的方法，将水平多层土等效为二层土壤，然后对矩形混凝土内任意形状的复合接地网的接地电阻，提出2种处理方法，第1种方法是建立分界面上的积分方程，然后用矩量法离散，并用有限面积来代替二层土壤无限大分界面进行求解．第2种方法是用无穷多个镜像代替二层土壤的作用，将二层土壤中的基础接地问题化为均匀土壤中的基础接地问题进行求解．应用静电场和恒定电流场的相似性，论述了第1种方法的实现过程，包括积分方程的建立，矩量法离散，奇点的处理，以及离散后的代数方程式等．编制了能计算矩形混凝土内任意形状复合地网接地电阻的程序，用文献[1，2]的计算结果，检验了方法的正确性．     

双频Buck变换器参数对系统性能的影响

双频Buck变换器中存在两组不同开关频率的功率器件，其中一组工作在高频，用于提高动态响应速度和稳态精度；另一个组工作在低频，对高频Buck单元中的电流分流，承担输出功率的任务，同时可以降低损耗。双频Buck变换器可以在提高系统性能的同时提高系统效率，适合于大功率场合的应用，其高低频率及参数对系统性能有重要影响。文中对双频Buck变换器中的高低频率、电路参数对系统性能的影响进行了理论分析，确定了参数设计原则。结果表明，双频Buck变换器的稳态和动态性能与单个高频Buck变换器相同。大量的仿真结果和实验证明了理论分析的正确性。     

水分对垃圾焚烧影响的实验研究

以层燃-流化复合垃圾焚烧为研究背景,利用实验方法,从垃圾干燥、层燃、流化燃烧3个方面研究了水分对垃圾焚烧过程的影响。垃圾中的过多水分导致垃圾的干燥过程延长,阻碍了垃圾的起燃,吸水性强的垃圾携带较多水分比吸水性弱的垃圾更能阻碍燃烧。在低温层燃状态下,因水煤气反应等作用,CO生成量随着含水率的增加而增加,高温下由于H2O能促进CO的氧化反应,CO随着含水率的增加而降低。高挥发分PVC、PS、木屑等燃料在层燃状态下可产生较高的CO。随着H2O的增加,N向NO、H向CH4的转化率多呈增加的趋势。而在流化燃烧状态下,随着水分的增加,CO降低,NO降低,表明H2O分子在流化床内对燃烧在机理上有强化作用。     

广义Tellegen定理在保留非线性电流注入型潮流计算中的应用

广义Tellegen定理只与物理系统所建立的数学模型有关,与该物理系统属性无关,因而广泛地应用于电力系统中。其小扰动定理为电力系统潮流计算提供了可能。保留非线性电流注入型的潮流计算就是将节点注入电流方程Taylor级数展开,并保留到二阶项,得到含有非线性项的修正方程式。在此基础上,利用广义Tellegen定理的小扰动定理,给出新的修正方程式,从而简化了求解过程。仿真结果表明,在保持计算精度和收敛性不变的情况下,提高了潮流计算速度,同时拓宽了广义Tellegen定理的应用领域。     

基于自适应逆控制的有源滤波器合成阻性负载

电力系统电网电压总存在畸变和不平衡，有源电力滤波器(Active power filter, APF)对谐波和无功进行补偿时，采用传统的正弦电流合成(Sinusoidal Current Synthesis，SCS)方法，公共连接点处的电压畸变会导致谐波传输的问题。而采用阻性负载合成(resistive load synthesis，RLS)方法，补偿后的主电流与实际的电网电压具有相同的波形，系统特征表现为阻性，可以有效的阻尼系统中的谐波传输。文中将自适应逆控制的方法应用于APF的控制来合成阻性负载，在补偿谐波和无功的同时，阻尼系统的谐波传输,将系统的功率因数校正为1。采用自适应逆控制方法，不需要知道广义有源滤波器的确切参数，逆控制器系统可以自动跟踪电路参数而实时建模。仿真和实验结果证实所提出的算法的有效性。     

Voltage sag mitigation in an Indian distribution system using dynamic voltage restorer

Now a day’s most power quality problems in distribution systems are related to voltage sags. Hence, diverse solutions have been tried to compensate these voltage sags to circumvent financial losses due to voltage sag at industries. Dynamic voltage restorers (DVRs) are now becoming more recognized in industries to diminish the impact of voltage sags to sensitive loads. The DVR, which is placed in series with a sensitive load, must be able to react speedily to a voltage sag if end users of sensitive equipment are to experience no voltage sags. This paper discusses the use of series reactive injection as a voltage regulator. The proposed approach is to develop analytical aspects and to illustrate these by an example of a real Indian distribution system. Voltage sag can be eliminated by continuously injecting very small voltage profile to the system. The scheme combines the method of instantaneous symmetrical components and complex Fourier transform relations. The proposed technique, based on half-cycle averaging, can mitigate voltage sag at desired locations in distribution systems. The proposed methodology is applied in a 4 bus system and a real Indian distribution system.