水泵水轮机旋转失速现象综述北大核心CSCD

旋转失速是水泵水轮机等旋转流体机械内部流动中普遍存在的不稳定现象。本文综述了水泵水轮机在水轮机工况运行过程中的旋转失速现象的主要特征及其传播特性。一方面,本文详细介绍了水泵水轮机旋转失速的基本概念、产生条件、形成机理以及失速团的传播和发展。另一方面,本文综述了识别旋转失速的常用方法,包括压力脉动时域和频域信号分析、气泡与线簇可视化实验等。为了进一步探究旋转失速对机组稳定性的影响,文章最后提出了两个在旋转失速研究中值得关注的问题。     

水泵水轮机工况转换期的振动现象

<正> 1引言就水电站大型水力机械的设计、制造、运行来说,了解激振力、机组性能以及与振动有关的各个部件越来越重要。一般来说,振荡激励源于流体的暂态特性,它主要又来源     

水泵水轮机的过渡现象及运行控制

<正> 1 引言水力机械的能量介质是比重较大的水,加之流道又较长,因此,在起动、停机、甩负荷等过渡状态下优先考虑的多数与水锤现象有关。尤其是在以下将要叙述的水泵水轮机中,与非设计点上的 S 型特性和逆流特性紧密相关,这些特性呈现更加复杂的状态。另     

仙游抽水蓄能电站水泵水轮机设计

从水力设计、结构设计、过渡过程等方面介绍了东方电机在仙游抽水蓄能电站水泵水轮机研制过程中所采用的设计技术及一些成果。包括提高水泵水轮机能量性能,提高驼峰余量,改善S形特性等方面的CFD方法;转轮、轴承、主轴密封、导水机构等的结构特点;过渡过程计算方法和优化实践等。     

叶轮机械旋转失速研究进展

介绍了目前旋转失速的理论模型、实验和数值模拟研究成果,总结了失速先兆与主动控制的关键问题,包括不同的先兆形式与诱发机制,泄漏涡与失速产生的关联性等,指出未来研究方向应主要侧重于叶轮机械旋转失速先兆的发生机理及影响因素、流固耦合研究及主动控制技术工程化研究。     

水泵和水泵—水轮机的试运行

本文提出了水泵—水轮机首次起动试运行最佳的典型程序,准备工作(包括各部分检查)。开始,先在无水情况下操作试验,一直到正式起动,超速激励、空载、同期以及带负荷和甩负荷试验等一整套试验和测量内容,为运行培训,合同验收提供了标准。文中还指出了在试验运行中曾经发生过的几个问题,如渗漏、淹灌、操作不当造成厂房被淹、动平衡问题、功率摆动、机械轴封不良、以及调速器故障和调相运行不成功等问题。可供抽水蓄能电站参考。     

水轮机和水泵/水轮机的变速运行

本文论述了水轮机和水泵/水轮机采用变速运行后所取得的效益,分析了采取的措施和存在的问题,指出了变速运行不仅适于在电网中小型水轮发电机上采用,也适于水头变化大的抽水蓄能机组。从我国水利资源和技术发展的情况来看,变速运行在电网中的小水轮机上可以得到广泛的采用。     

水轮机工况下的水泵水轮机静态稳定

S区是水泵水轮机与常规水轮机转轮主要的差异，是导致水泵水轮机稳定性问题的主要因素之一。本文从单位流量Q11、单位力矩T11和单位转速n11基本定义出发，分别导出了全特性曲线上单位流量Q11与单位力矩T11对单位转速n11的导数，根据单位流量Q11与单位力矩T11的微分特征，结合定导叶开度情况下水轮机工况流量Q-工作水头H和反水泵工况流量Q-工作扬程H特性曲线，分别获得了水轮机工况和反水泵工况机组稳定运行需满足的条件。采用静态稳定理论获得了水泵水轮机在水轮机工况和反水泵工况稳定运行时工作水头/扬程扰动量所满足的关系，在此基础上给出了水轮机稳定运行需满足的条件并定义了S区。研究结果为建立水泵水轮机在水轮机工况的稳定运行区提供了技术支撑。     

水泵水轮机转轮内水泵工况紊流分析

本文基于 N - S方程和 K—ε紊流模型 ,对于所选择的五个工况点 ,采用贴体座标系和交错网格系统 ,用 SIMPL EC算法对水泵水轮机转轮内部的紊流进行数值模拟 ,得出了转轮内部流场和压力场的分布。将计算结果用 Tecplot7进行处理 ,分析其在不同工况点时内部的流动状态和压力分布     

偏工况下离心泵叶轮内失速特性研究

旋转失速是离心泵内部常见的一种不稳定流动现象,通常发生在小流量工况下,会引起水泵运行时的性能不稳定,严重时会引起整个泵系统的共振。采用CFD方法对某离心泵内的失速现象进行数值模拟,并从外特性曲线、内部流动状况及频域分析三个方面与已有的实验结果进行对比。采用阻塞系数来量化表达叶轮内部的失速状况。结果表明,在0.35倍最优流量（0.35Q0）下,在叶轮通道间存在着五个失速团,随着时间的推移,五个失速团在不同的通道之间以低于叶轮转频的转动频率在叶轮之间传播。对通道内部监测点的速度波动进行频域分析的结果表明,失速团的旋转频率约为叶轮转频的23.4%,即失速团的旋转角速度为叶轮转速的4.68%。而在0.41Q0工况下,由于此时造成失速的初始扰动还不足以使失速团相对于叶轮发生转动,离心泵内部出现了“固定失速”的现象。相比于旋转失速,在发生固定失速时,叶道中的阻塞系数波动较小,因此这是一种相对稳定的失速现象。同时,叶轮叶片数对失速的类型有着决定性的影响。     

改善失速工况下轴流泵水力性能的研究

基于非定常的RANS方程,采用滤波器湍流模型对某一轴流泵模型在不同工况下的内部流场进行数值计算。通过与模型泵水力性能试验结果进行对比,发现与标准k-ε模型相比,无论在最优工况点还是在不稳定的失速工况区,滤波器湍流模型具有较高的预测精度。利用沟槽流动控制技术对进口锥管进行结构优化,研究其对轴流泵水力性能以及叶轮进口前的速度场和压力脉动的影响。结果表明,沟槽流动控制技术能够减弱叶轮进口前的预旋,提高叶轮进口入流的均匀性,同时可以有效降低叶轮进口前强烈的低频压力脉动,从而改善失速工况下轴流泵的水力性能。     

Internal electrical fault detection techniques in DFIG-based wind turbines: a review

The keys factor in making wind power one of the main power sources to meet the world’s growing energy demands is the reliability improvement of wind turbines (WTs). However, the eventuality of fault occurrence on WT com ponents cannot be avoided, especially for doubly-fed induction generator (DFIG) based WTs, which are operating in severe environments. The maintenance need increases due to unexpected faults, which in turn leads to higher operating cost and poor reliability. Extensive investigation into DFIG internal fault detection techniques has been carried out in the last decade. This paper presents a detailed review of these techniques. It discusses the methods that can be used to detect internal electrical faults in a DFIG stator, rotor, or both. A novel sorting technique is presented which takes into consideration different parameters such as fault location, detection technique, and DFIG modelling. The main mathematical representation used to detect these faults is presented to allow an easier and faster under standing of each method. In addition, a comparison is carried out in every section to illustrate the main differences, advantages, and disadvantages of every method and/or model. Some real monitoring systems available in the market are presented. Finally, recommendations for the challenges, future work, and main gaps in the field of internal faults in a DFIG are presented. This review is organized in a tutorial manner, to be an effective guide for future research for enhancing the reliability of DFIG-based WTs.     

海水淡化高转速泵作透平的压力脉动分析北大核心CSCD

离心泵反转作透平是海水淡化能量回收一体机的核心动力部件之一,运行时的压力脉动是机组产生振动和噪声的主要因素之一。本文以高转速离心泵反转作透平为研究对象,采用SAS-SST-CC湍流模型,对其进行整机流道三维非定常流动数值计算,通过流场分析及压力脉动频谱分析,探讨该透平在运行时的非定常流动特性。非定常数值计算结果显示,蜗壳内多测点的压力脉动主频均为叶片通过频率,说明蜗壳内压力脉动主要由转轮和蜗壳隔舌间的动静干涉引起;旋转转轮域内8个叶片间流道中各布置了6个测点,各相似位置测点间的压力脉动峰峰值最大相差10.3%,说明对称的旋转转轮内的流动分布严重不均,这些旋转测点的脉动频率主要为叶频8倍频附近的主频或次主频,说明转轮与蜗壳间的动静干涉、叶片流道间的漩涡是引起转轮内压力脉动的主要因素,且局部漩涡引起的压力脉动强于转轮动静干涉造成的。结果表明,转轮内压力脉动比蜗壳内明显剧烈,旋转转轮内的压力脉动是机组振动主要水力原因。     

Internal electrical fault detection techniques in DFIG-based wind turbines: a review

Offshore wind farms (OWFs) have received widespread attention for their abundant unexploited wind energy potential and convenient locations conditions. They are rapidly developing towards having large capacity and being located further away from shore. It is thus necessary to explore effective power transmission technologies to connect large OWFs to onshore grids. At present, three types of power transmission technologies have been proposed for large OWF integration. They are: high voltage alternating current (HVAC) transmission, high voltage direct current (HVDC) transmission, and low-frequency alternating current (LFAC) or fractional frequency alternating current transmission. This work undertakes a comprehensive review of grid connection technologies for large OWF integration. Compared with previous reviews, a more exhaustive summary is provided to elaborate HVAC, LFAC, and five HVDC topologies, consisting of line-commutated converter HVDC, voltage source converter HVDC, hybrid-HVDC, diode rectifier-based HVDC, and all DC transmission systems. The fault ride-through technologies of the grid connection schemes are also presented in detail to provide research references and guidelines for researchers. In addition, a comprehensive evaluation of the seven grid connection technologies for large OWFs is proposed based on eight specific indicators. Finally, eight conclusions and six perspectives are outlined for future research in integrating large OWFs.     

A case study of replacing steam turbines with LCI-typevariable-speed drives

The problems and experiences associated with the installation, start-up, and operation of 7000 HP 1800 r/min and 3600 HP 6000 r/min synchronous motors using load commutated inverter (LCI) variable-speed controllers are examined. The application of new technology in existing process units can present some unusual and sometimes perplexing challenges. The steep learning curve, and the fact that most projects are time and money driven, all contribute to the hurdles that must be overcome. The described application of LCI variable-speed drives covered all of the factors. Some of the problems and concerns encountered with this project resulted from equipment previously installed, coupled with the dynamics of the electrical, instrumentation, and process systems. When planning the application of variable-speed drives, factors such as electrical system disturbances, impact of harmonics on the existing equipment, training, commissioning, operator acceptance, craft training, and spare parts all need to be taken into consideration     

汽轮机组合理检修周期研究

汽轮机组实施计划检修耗时长、费用高，大修揭缸后往往发现汽轮机本体及辅助设备健康状况良好。为了科学合理地制定检修周期，研究提出确定汽轮机检修周期的理论计算法、可靠性分析法、等效运行小时(EOH)计算法及极限热耗率方法，确定机组最佳大修周期的理论方法是依据RCM理论确定设备的可靠度．再根据可靠度确定最佳检修周期；按等效运行小时来确定汽轮机组大修间隔，考虑了蠕变寿命损耗和低周疲劳寿命损耗的影响并提出300MW机组等效运行小时推荐计算公式；根据实际运行热耗与极限热耗率对比，可以确定检修时间。