Fluid–structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load

Müller, Andres; Favrel, Arthur; Landry, Christian R.; Avellan, François

doi:10.1016/j.jfluidstructs.2016.11.018

Cited by 98 publications

(60 citation statements)

References 23 publications

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“…When the flow rate in the machine is regulated to generate more or less electricity than in the BEP, a swirl in the flow at the turbine runner outlet appears, especially in Francis turbines, which for certain condition could lead to draft tube surge cavitation or vortex rope [3,4]. This phenomenon has been studied for many years [5,6], experimentally in laboratory and by means of CFD (Computational Fluid Dynamics) simulations.…”

Section: Introductionmentioning

confidence: 99%

“…However, when the vortex rope occurs over the BEP (more flow rate), the core is centered in the runner cone [5] rotating at the opposite direction than the runner. In this case, the convective or asynchronous component is less important than in the part load vortex rope, but it has a large synchronous component.…”

Section: Introductionmentioning

confidence: 99%

“…In this case, the convective or asynchronous component is less important than in the part load vortex rope, but it has a large synchronous component. This phenomenon is able to self-excite the natural frequencies of the hydraulic circuit [5] affecting the whole system stability. It is known as Overload Instability [9], and its consequences over the structure and the power swing are even larger than in the part load instability since the flow passing through the runner is larger, as well as the propagated pressure pulses.…”

Section: Introductionmentioning

confidence: 99%

“…Both part load and overload instabilities are dependent on the net head of the machine [5,6], especially on the lower reservoir level. Therefore, for different net heads, they can appear at different generating powers.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

et al. 2017

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Abstract:Hydropower plays a key role in the actual energy market due to its fast response and regulation capacity. In that way, hydraulic turbines are increasingly demanded to work at off-design conditions, where complex flow patterns and cavitation appear, especially in Francis turbines. The draft tube cavitation surge is a hydraulic phenomenon that appears in Francis turbines below and above its Best Efficiency Point (BEP). It is a low frequency phenomenon consisting of a vortex rope in the runner outlet and draft tube, which can become unstable when its frequency coincides with a natural frequency of the hydraulic circuit. At this situation, the output power can significantly swing, endangering the electrical grid stability. This study is focused on the detection of these instabilities in Francis turbines and their relationship with the output power swings. To do so, extensive experimental tests for different operating conditions have been carried out in a large prototype Francis turbine (444 MW of rated power) within the frame of the European Project Hyperbole (FP7-ENERGY-2013-1). Several sensors have been installed in the hydraulic circuit (pressure sensors in the draft tube, spiral casing, and penstock), in the rotating and static structures (vibration sensors, proximity probes, and strain gauges in the runner and in the shaft), as well as in the electrical side (output power, intensity, and voltage). Moreover, a numerical Finite Element Method (FEM) has been also used to relate the hydraulic excitation with the output power swing.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

et al. 2017

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“…When the pressure fluctuation passes through the flow passage parts and structures, the vibration of the unit, the period swing of the shaft, and the vibration of the head cover of the Francis turbine may be caused [6,7]. When the pressure fluctuation resonates with the water body in the pressure pipeline, it will cause the vibration, output oscillation of the hydropower generating unit, and even have an influence on the electric power system [8,9]. In recent years, some large and giant Francis turbines have been put into operation, whose size and specific speed have increased, while relative stiffness has weakened; hence the hydraulic instability problems have become more serious [10].…”

Section: Introductionmentioning

confidence: 99%

A Novel Multidimensional Frequency Band Energy Ratio Analysis Method for the Pressure Fluctuation of Francis Turbine

Wang

Liang

Yue

et al. 2018

Mathematical Problems in Engineering

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The pressure fluctuation has multiple influence on the steady operation of Francis turbine, and the impact degree varies with the operation condition. In this paper, for the analysis of pressure fluctuation in the Francis turbine, a novel feature extraction method of multidimensional frequency bands energy ratio is proposed based on Hilbert Huang Transform (HHT). Firstly, the pressure fluctuation signal is decomposed into intrinsic mode functions (IMFs) by EEMD. Secondly, the Hilbert marginal spectrum is utilized to analyze the frequency characteristics of IMFs. Then, according to the inner frequency of IMFs, each of them is divided into high, medium, or low frequency band which are constructed based on the frequency characteristic of the pressure fluctuations in the Francis turbine. Afterward, the energy ratio of each frequency band to the original signal is calculated, which is to realize the feature extraction of multidimensional frequency band energy ratio. Actual applications verify that this method not only can extract the time-frequency characteristics but also can analyze the condition feature of the pressure fluctuation. It is a novel method for extracting the feature of pressure fluctuation in the Francis turbine.

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Study of the inhibitory effect of a soft cushion on the propagation of pressure pulsation in pumped storage power stations

Yang,

Wang,

Yang

et al. 2023

Earthquake Engineering and Resilience

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High‐frequency pressure pulsations are hydraulic phenomena that are frequently observed in pumped storage power stations. These pulsations can propagate through the steel pipes, concrete lining, and the surrounding rock system, which in turn may have detrimental effects on the environment, such as noise pollution, and relocation of the local residents. This paper proposes a vibration‐damping concept that involves wrapping a local soft cushion layer outside the buried steel pipe; this layer could partially eliminate the pressure fluctuations in the headrace tunnel, thereby reducing the ground vibrations caused by the pressure pulsations. In this study, the finite element method was used to model the propagation of vibrations in the surrounding rock and fluid‐filled pipes, including static simulation of the structure, and dynamic simulation of the surrounding rock. The simulation results suggest that adding an appropriate local soft bedding layer can effectively reduce the ground vibrations by more than 60% and the possible surface noise within the standard vertical vibration norms. The inhibitory effect of the soft cushion on the propagation of vibrations is determined by the wrapping angle, thickness, and material of the bedding layer. This effect increases with increasing wrapping angle and thickness of the bedding layer, and decreases with increasing elastic modulus of the material. After the addition of the bedding layer between the steel pipe and concrete lining, the pressure in the inner pipe is primarily borne by the steel lining rather than the coupling of the steel lining, concrete lining, and the surrounding rock. Hence, the thickness of the part of the steel liner in contact with the soft bedding layer should be increased. In addition, the thickness variations in the steel pipe joints should be smooth to avoid stress concentration.

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Fluid–structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load

Cited by 98 publications

References 23 publications

Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

Power Swing Generated in Francis Turbines by Part Load and Overload Instabilities

A Novel Multidimensional Frequency Band Energy Ratio Analysis Method for the Pressure Fluctuation of Francis Turbine

Study of the inhibitory effect of a soft cushion on the propagation of pressure pulsation in pumped storage power stations

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