浅析发电机端电压降低故障现象分析及处理

为了提高发电机端运行安全性,降低发生故障的概率,以QFSN-660-2三相同步汽轮发电机为例,讨论电压降低故障现象,阐述该故障的原理与原因,以及在运行过程中出现故障的表现,提出解决电压降低故障的处理方法与预防建议.电压降低故障对于发电机端运行的影响,需要在今后设备运行与管理中加强关注,重点预防与解决,才能够实现汽轮发电机的稳定运行.     

基于故障树和概率神经网络的风电机组故障诊断方法

风电机组各传动设备之间耦合性强,故障发生的原因复杂、多样,使用单一的故障诊断方法受自身的局限性影响,诊断效果不太理想。针对这一问题,通过分析风力发电机组转速故障数据及其影响因素,以风力发电机转速超限故障为例,提出一种基于故障树和概率神经网络的风电机组发电机转速超限故障智能诊断方法。首先,给出多层故障树构建方法,使用故障树分析法得到故障模式。然后,根据故障树节点关系规则和故障模式,提取风力发电机运行数据的特征值,建立概率神经网络的故障诊断模型,根据实际运行故障样本训练网络,将训练后的网络用于故障诊断。现场实验表明,基于故障树和概率神经网络算法对于风力发电机转速故障诊断准确率显著。     

300MW汽轮机高压缸通流部分故障的热参数模糊诊断

分析了３００ＭＷ汽轮机高压缸通流部分故障与热力过程参数的关系，提出了对汽轮机通流部分故障分层次模糊诊断的方法，并用电厂运行中采集到的实际故障参数对这种方法进行了考核，得到了比较满意的结果。     

基于AR-Hankel矩阵的风力发电机早期故障诊断方法研究

针对风力发电机故障早期阶段,故障特征不明显,继电保护装置检测不到相关电气量异常的问题,文章提出了基于AR模型、Hankel矩阵和奇异值分解的风力发电机早期故障诊断方法。该方法先对主轴径向振动信号进行总体平均经验模式分解,再按照互相关准则选择若干个固有模态函数建立AR模型,然后对自回归系数构建Hankel矩阵并作奇异值分解,将奇异值作为故障特征输入支持向量机判断发电机的运行状态。试验结果表明,该方法能对直驱风力发电机正常运行、定子线圈匝间短路、发电机主轴偏心、发电机轴承磨损4种状态进行准确诊断。     

大型电站对分式凝汽器故障的征兆提取和模糊诊断研究

针对大电站对分式凝汽器的结构特点及现场凝汽系统构成和实际测点布置,运用凝汽器有关原理,建立了对分式凝汽器的动态仿真数学模型,并首次运用基于模型的故障仿真方法结合现场运行经验总结并完善了对分式凝汽器的典型故障征兆集,对故障征兆的具体表达方法进行了有益的探讨,在此基础上运用模糊模式识别方法实现对分式凝汽器故障诊断,改进了模糊诊断的隶属函数,通过诊断实例比较了改进前后的诊断效果。     

自适应学习率的BP网络算法及其在汽轮发电机组故障模糊诊断中的应用

针对ＢＰ网络的不足，提出了自适应学习率的ＢＰ网络算法，从根本上解决了ＢＰ网络学习率的取值问题和收敛速度慢的问题，并有效地克服了ＢＰ网络易陷入局部最小点缺点，采用这种改进算法成功地实现了对汽轮发电机线故障的模糊诊断。     

模糊理论在风力发电机组故障诊断中的应用

模糊理论为基础，结合风力发电机组的实际运行工况、现场运行人员和专家的经验，分析了故障与征兆之间的模糊关系，形成了模糊故障诊断规则，建立了风力发电机组模糊故障诊断自适应修正数学模型。最后对一个具体故障实例加以分析，验证了模糊理论在风力发电机组故障诊断中的可行性。     

基于模糊聚类分析的燃气轮机振动故障诊断研究

通过对燃气轮机振动故障的研究分析,提出一种基于模糊聚类分析的燃气轮机振动故障诊断实践方案。针对某海上平台石油作业区单轴燃气轮机的现场运行状况,通过比利时LMS信号采集分析仪进行目标机组的振动测试,运用模糊聚类分析原理对振动故障进行分类,并充分利用各种振动故障征兆,建立燃气轮机振动故障模糊关系方程,通过计算查找机组故障原因,更准确地进行燃气轮机的故障识别及诊断。通过现场验证,对于燃气轮机发电机组的可靠性运行产生一定的积极作用。     

发电机定子单相接地故障诊断模型研究与设计

发电机定子单相接地故障较为常见,其对发电机安全运行构成威胁,如何设计发电机定子单相接地故障诊断模型对判断发电机安全可靠运行有重要意义。本文从软件设计的角度综合考虑包括事件描述、数据输入和输出、所用算法及逻辑关系等,未软件实现发电机定子接地故障诊断判断提供方法和基础。     

黑体炉系统故障诊断专家系统实现问题

为了实现黑体炉系统已发故障或潜在故障的快速高效诊断,根据黑体炉系统运行过程特征参数知识表示的模糊特性,建立了多库多层次方式的知识库,并采用黑体炉故障类型诊断的反向推理和故障原因分析及故障消除措施正向推理相结合的混合推理机制设计了总体目标推理和级目标推理相结合的推理机.该系统采用Visual Basic6.0进行编程,在windows xp平台上运行.应用效果表明,黑体炉故障诊断专家系统的预报准确率较高,具有较大的实用性.     

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.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Contents in Volume 23,2014

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汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.