基于超声波法的长距离超高压GIL电弧故障定位

武汉市谭鑫培路城市地下综合管廊气体绝缘金属封闭输电线路(GIL)工程建成后将成为世界上最长的气体绝缘输电线路,一旦发生电弧击穿,将严重影响整条输电线路的电能输送,造成很大的经济损失,因此有必要对其电弧故障定位策略进行研究.通过比较各类常用GIL故障定位方法,选择超声波法作为故障定位方法,对超声波法定位技术的理论进行了研究,包括GIL击穿时的超声信号特征以及超声信号在GIL中的传播特性,根据工程实际情况,提出了基于超声波法的电弧故障定位策略及系统安全性设计,以实现故障的精确定位和快速修复.     

EMD在LabVIEW中的实现及其在水轮机主轴振动信号分析中的应用

针对LabVIEW中缺少经验模态分解(EMD)算法模块的问题,对LabVIEW进行了二次开发,建立了基于LabVIEW的EMD模块,为振动故障信号分析提供了有效的工具,进而以水轮机故障信号的振动特征和故障产生机理为依据,将此算法运用于水轮机主轴振动信号分析,以河北省西达水电站水轮机主轴振动数据为基本资料,对分解得到的高频本征模函数(IMF)分量做包络谱分析,提取故障信息,并与轴心轨迹分析方法相结合加以验证。结果表明,该方法能够有效判别出水轮机主轴故障类型,可应用于水轮机主轴振动信号分析。     

基于EEMD及分形方法的轴承振动信号分析

为对具有强烈非线性特征的轴承振动信号做出准确的故障识别,基于分形理论,采用辅助经验模态分解(Ensemble Empirical Mode Decomposition,EEMD)对信号进行降噪预处理,采用G-P算法分析轴承不同状态下振动信号关联维数。研究表明:基于EEMD的降噪方法可有效对振动信号进行降噪;轴承工作状态不同,其振动信号关联维数具有明显的可区分性,当轴承处于外环故障时,其关联维数最大为4.7,当轴承处于滚珠故障时,其关联维数最小仅为3.0,当轴承处于正常/内环故障时,其关联维数分别为4.0/3.2。因此,利用关联维数能定量识别轴承的不同故障状态及位置。     

核电厂气体绝缘金属封闭输电线路故障原因分析及解决措施

通过对国内某核电厂气体绝缘金属封闭输电线路(GIL)故障过程的分析,逐步定位出故障的起始点,确定出故障的根本原因。针对本次故障的起始点三支柱绝缘子,提出了缺陷排查的补充检测手段超声波局放试验和定期SF6气体成分分析试验,可对核电厂后续的安装调试及运行管理提供借鉴。     

基于改进小波包的风电机组齿轮箱复合故障特征提取研究

针对小波包分解振动信号时会产生频谱混叠从而导致齿轮箱复合故障特征能量谱提取困难的问题,提出基于旁路滤波改进小波包的方法对双馈风电机组齿轮箱复合故障振动信号进行研究,并以风电场的大量齿轮箱振动信号为基础,运用传统小波包及旁路滤波改进小波包分别对齿轮箱振动信号提取特征能量谱。实验结果表明：运用旁路滤波改进小波包对双馈风电机组齿轮箱复合故障振动信号进行分析,可有效避免传统小波包分析振动信号的频谱混叠现象,准确提取每种故障状态的特征能量谱。     

基于EEMD的变压器振动与声音信号IMF峭度特征量提取方法

针对变压器振动问题,提出了一种基于集合经验模态分解(EEMD)的本征模函数(IMF)峭度特征量提取方法,并运用相关系数法、快速谱峭度图法提取敏感IMF分量。提取试验变压器正常、铁心松动故障状态下的振动、声音信号的特征量,研究变压器在正常、故障状态下这两种信号特征量分布情况;分析实际运行中出现铁心磁路故障、铁心多点接地故障状态的变压器的IMF峭度特征。结果表明,提出的特征量提取方法可同时反映频域、时域特性;在不同故障条件下,振动与声音信号的特征量变化不同,二者可相互补充,研究两种信号更有利于变压器状态的判定。     

HHT与RBF神经网络在离心泵故障振动信号处理中的应用

根据离心泵故障振动信号的特点,提出了一种Hilbert-Huang变换(HHT)和径向基(RBF)神经网络相结合的离心泵振动信号故障诊断新方法。首先,将离心泵振动信号时间序列数据经验模态分解(Empirical Mode Decomposition,简称EMD),然后经过Hilbert-Huang变换获得各模态(Intrinsic Mode Functions,简称IMF)的能量,并以“能量比”为元素,利用能量比构造离心泵振动信号的特征向量可以很好刻画不同振动故障信息;应用RBF神经网络建立了从特征向量到故障模式之间的映射实现故障的诊断,对于离心泵的正常状态、质量不平衡、转子不对中和基础松动故障具有很高的诊断率。实验研究结果表明,该方法可以有效地对离心泵振动信号进行诊断。     

基于非高斯性强度的风电齿轮箱故障特征提取

研究了风电机组齿轮箱的复杂振动信号并提取故障特征.由Gabor变换进行滤波和重构,抑制振动信号中的啮合频率及其谐波成分,对以边带成分、随机成分、固有频率成分为主的重构信号进行双谱分析,揭示齿轮正常状态与点蚀故障时振动信号的非高斯性差异,并提取到非高斯性强度特征值.结果表明：齿轮故障会引起振动信号中非高斯分布成分发生变化,由滤波信号提取到的非高斯性强度特征值对齿轮点蚀故障十分敏感,该计算方法较为便捷,具有一定的工程实用价值.     

开关柜局部放电传感器监测方案及仿真研究

基于开关柜绝缘故障的原理,提出了一种改进的地电波(T EV)局部放电检测方法,传感器采用非侵入式检测手段实现在线检测,可以发现一些潜在的绝缘故障.对开关柜内部局部放电位置进行研究,结合传感器数据采集特点进行开关柜的局部放电监测,优化监测效果.仿真及试验结果表明:前柜门左侧中央是最佳的传感器安装位置;作为一种非侵入式检测手段,其对于开关柜内部是否存在放电性绝缘故障,具有灵敏度高、成本低、安装方便等优势,十分适合高压开关柜的带电检测.     

开关柜内部绝缘缺陷的检测研究

在实际运行中,开关柜的绝缘故障和绝缘劣化主要由局部放电引起,鉴于现场运行中设备的局部放电与绝缘状态的检测技术还不成熟,提出了采用脉冲电流法测定PC值(视在放电量),TEV技术测定dB值,并利用干扰源产生的4种复合干扰来模拟实际开关柜运行中的干扰,测得了金属开关柜基于各放电点的dB-PC数据库,极大地方便了实际运用中实测暂态对地电压(TEV值)和脉冲电流(PC值)之间的转换,利用这种转换可方便地了解局部放电的情况。     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Economie d'énergie en trigénération

Trigeneration is defined as the production of three useful forms of energy—heat, cold and power—from a primary source of energy such as natural gas or oil. For instance, trigeneration systems typically produce electrical power via a reciprocating engine or gas turbine and recover a large percentage of the heat energy retained in the lubricating oil, exhaust gas and coolant water systems to maximize the utilization of the primary fuel. The heat produced can be totally or partially used to fuel absorption refrigerators. Therefore, trigeneration systems enjoy an inherently high efficiency and have the potential to significantly reduce the energy-related operation costs of facilities. In this paper, we describe a model of characterization of trigeneration systems trough the condition of primary energy saving and the quality index, compared to the separate production of heat, cold and power. The study highlights the importance of the choice of the separate production reference system on the level of primary energy saving and emissions reduction.     

Mineralogical characterization of the intraseam layers of Lofoi lignite deposits in Florina basin (western Makedonia,northwest Greece)

The mineralogical composition of intraseam layers from Lofoi lignite deposits (northwest Greece) is the subject of the present study. The samples were examined by means of X-ray diffraction (XRD), thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA), and Fourier transform infrared (FT-IR) spectrometry. The clay minerals prevail in most samples, with illite-muscovite being the dominant phase, and kaolinite and chlorite being the other major clay components. No smectite was found. Quartz and feldspars, dominate in two cases. The studied materials are characterized as clays to clayey sands, showing significant similarities with the intraseam layers of the adjacent Achlada lignite deposits.     

Innovative methodologies in renewable energy: A review

This paper is concerned with innovative approaches to renewable energy sources computation methodologies, which provide more refined results than the classical alternatives. Such refinements provide additional improvements especially for replacement of fossil energy usages that emit greenhouse gas (GHG) into the atmosphere leading to climate change impact. Current knowledge gap among each renewable energy source calculation is rather missing fundamentals of plausible, rational, and logical explanations for the interpretation of results. In the literature, there are rather complicated and mechanically applicable methodologies, which require input and output measurement data match with missing physical explanations. The view taken in this review paper is to concentrate on quite plausible, logical, rational, and effectively applicable innovative energy calculation methodologies with simplistic fundamentals. For this purpose, a set of renewable energy methodological approaches is revisited with their innovative structures concerning solar, wind, hydro, current, and geothermal energy resources. With the increase in the renewable energy utilizations to combat the undesirable impacts of global warming and climate change, there is a need for better models that will include physical environmental conditions and data properties in the probabilistic, statistical, stochastic, logical, and rational senses leading to refined and more reliable estimations with application examples in the text. Finally, new research directions are also recommended for more refined innovative energy system calculations.     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.