Hydroacoustic modelling and numerical simulation of unsteady operation of hydroelectric systems
Hydroacoustic modelling and numerical simulation of unsteady operation of hydroelectric systems
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DOI：
10.5075/epfl-thesis-3751
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
C. Nicolet
中科院分区：
文献类型：
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作者：
C. Nicolet
1999年，水力发电占世界发电量的19%，预计在今后30年中，绝对发电量将大幅增长。弗朗西斯水轮机由于其广泛的应用范围而在水电生产中发挥着重要作用。由于能源市场的放松管制，水力发电厂越来越多地受到非设计运行，启动和关闭和新的控制策略。因此，弗朗西斯涡轮机发电厂的运行会导致瞬变现象、共振或不稳定的风险。因此，对这些传播现象的理解至关重要。这项工作是对弗朗西斯涡轮机电站的水声建模的贡献，用于调查上述问题。文件的第一部分介绍了水力发电厂的动态行为和瞬态分析的建模。因此，一维模型的基本管道是来自控制方程，即动量和连续性方程。使用适当的数值方案导致一个离散模型的管道组成的T形等效电路。通过与控制方程的解析解比较，确定了管道离散模型在频域中的精度。建模方法扩展到液压元件，如阀门，调压室，调压井，空气容器，空化发展等，然后，建模的弗朗西斯，冲击式和轴流转浆式水轮机瞬态分析的目的。该建模基于涡轮机静态特性的使用。液压元件模型在EPFL软件SIMSEN中实现，该软件用于电气装置的仿真。水力模型的验证后，在水力发电厂的瞬态现象进行了研究。看来，无论是液压或电气部分的标准单独的研究是有效的设计目的，而完整的水电模型是必要的涡轮机调速器的优化。本文件的第二部分涉及弗朗西斯涡轮机发电厂中可能的共振或运行不稳定性的建模和分析。对弗朗西斯涡轮机运行固有激励源的审查表明，尾水管和转子-定子相互作用压力波动是主要问题。由于在低频下尾水管中产生的空化涡带引起的部分负荷压力波动的模型已经建立，因此重点放在较高频率的现象上，例如较高的部分负荷压力波动和转子与定子的相互作用或满载不稳定性。进行了三次水声调查。(i)本文采用水声模拟和高速流动显示的方法研究了缩尺模型弗朗西斯涡轮机在高部分负荷下的压力脉动。通过仿真指出了涡绳激励引起的试验台共振现象，同时通过可视化突出了空化涡绳在共振频率下的特殊运动和形状。提出了可能的激发机制的描述。(ii)对某4 × 400 MW抽水蓄能电站全负荷运行时的压力和功率波动进行了研究。整个系统的建模，包括液压回路，旋转惯量和电气安装提供了一个解释的现象和相关的条件的出现。建立了满负荷涡带的非线性模型，并进行了定性验证。(iii)在缩尺水泵水轮机模型的情况下研究了转子-定子干扰（RSI）。本文提出了一种基于定、转子间流量分配的模拟方法。该模型提供了无叶间隙中RSI压力波动模式，并能够预测蜗壳和内收管中的驻波。所提出的一维建模方法能够对水力发电厂的动态行为进行模拟、分析和优化。该方法已被证明是适当的瞬态和周期性现象的模拟能力。这种调查可以在项目的早期阶段进行，以评估可能的动态问题，并选择适当的解决方案，确保设施的最安全和最佳运行。
Hydropower represented in 1999 19% of the world electricity production and the absolute production is expected to grow considerably during the next 30 years. Francis turbines play a major role in the hydroelectric production due to their extended range of application. Due to the deregulated energy market, hydroelectric power plants are increasingly subjecting to off design operation, start-up and shutdown and new control strategies. Consequently, the operation of Francis turbine power plants leads to transients phenomena, risk of resonance or instabilities. The understanding of these propagation phenomena is therefore paramount. This work is a contribution to the hydroacoustic modelling of Francis turbine power plants for the investigation of the aforementioned problematic. The first part of the document presents the modelling of the dynamic behavior and the transient analysis of hydroelectric power plants. Therefore, the one-dimensional model of an elementary pipe is derived from the governing equations, i.e. momentum and continuity equations. The use of appropriate numerical schemes leads to a discrete model of the pipe consisting of a T-shaped equivalent electrical circuit. The accuracy in the frequency domain of the discrete model of the pipe is determined by comparison with the analytical solution of the governing equations. The modelling approach is extended to hydraulic components such as valve, surge tanks, surge shaft, air vessels, cavitation development, etc. Then, the modelling of the Francis, Pelton and Kaplan turbines for transient analysis purposes is presented. This modelling is based on the use of the static characteristic of the turbines. The hydraulic components models are implemented in the EPFL software SIMSEN developed for the simulation of electrical installations. After validation of the hydraulic models, transient phenomena in hydroelectric power plants are investigated. It appears that standard separate studies of either the hydraulic or of the electrical part are valid only for design purposes, while full hydroelectric models are necessary for the optimization of turbine speed governors. The second part of the document deals with the modelling and analysis of possible resonance or operating instabilities in Francis turbine power plants. The review of the excitation sources inherent to Francis turbine operations indicates that the draft tube and the rotor-stator interaction pressure fluctuations are of the major concern. As the modelling of part load pressure fluctuations induced by the cavitating vortex rope that develops in the draft tube at low frequencies is well established, the focus is put on higher frequency phenomena such as higher part load pressure fluctuations and rotorstator interactions or full load instabilities. Three hydroacoustic investigations are performed. (i) Pressure fluctuations identified experimentally at higher part load on a reduced scale model Francis turbine are investigated by means of hydroacoustic simulations and high speed flow visualizations. The resonance of the test rig due to the vortex rope excitation is pointed out by the simulation while the special motion and shape of the cavitating vortex rope at the resonance frequency is highlighted by the visualization. A description of the possible excitation mechanisms is proposed. (ii) A pressure and power surge measured on a 4 × 400 MW pumped-storage plant operating at full load is investigated. The modelling of the entire system, including the hydraulic circuit, the rotating inertias and the electrical installation provides an explanation of the phenomenon and the related conditions of apparition. A non-linear model of the full load vortex rope is established and qualitatively validated. (iii) The rotor-stator interactions (RSI) are studied in the case of a reduced scale pump-turbine model. An original modelling approach of this phenomenon based on the flow distribution between the stationnary and the rotating part is presented. The model provides the RSI pressure fluctuation patterns in the vaneless gap and enables to predict standing waves in the spiral case and adduction pipe. The proposed one-dimensional modelling approach enables the simulation, analysis and optimization of the dynamic behavior of hydroelectric power plants. The approach has proven its capability of simulating properly both transient and periodic phenomena. Such investigations can be undertaken at early stages of a project to assess the possible dynamic problems and to select appropriate solutions ensuring the safest and optimal operation of the facility.