A look at Francis runner blades response during transients

Gagnon, Martin; Nicolle, Jonathan; Morissette, Jean-François; Lawrence, Mark

doi:10.1088/1755-1315/49/5/052005

Cited by 22 publications

(23 citation statements)

References 2 publications

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“…Frequencies and amplitudes are normalized similar to the turbine-1 cases by using Eqs. (5) and 6, respectively. Figure 13 presents a spectrogram of the pressure data during load acceptance from the 70% to the 90% load operating condition.…”

Section: -13mentioning

confidence: 99%

“…4 Furthermore, hydraulic turbines experience unstable flow conditions and high amplitude pressure pulsations during the transient cycles. [5][6][7][8][9][10] The pressure amplitudes are primarily dependent on the instantaneous rate of the guide vanes' movements and the runner's speed. 11,12 For the load acceptance cycle, the power output from the hydraulic turbine increases by opening the guide vanes.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the unsteady pressure pulsations in the prototype Francis turbines during load variation and startup

Trivedi

Gogstad

Dahlhaug

2017

Journal of Renewable and Sustainable Energy

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speed. For the start-up cycle, the guide vanes are initially opened by a few percentages from a completely closed position. As the discharge to the runner increases, the runner starts spinning at a synchronous speed to that of the corresponding turbine. The generator then is coupled to the grid network at a minimum load. After synchronization, the power output is further increased to the set value by increasing the discharge to the runner. Unsteady pressure measurements observed during the transient cycles of a Francis turbine model indicated that a turbine could experience more than twice the pressure amplitudes observed at the best efficiency point (BEP). 13-15 Pressure measurements in a draft tube indicated that high amplitude pressure oscillations occur during the load variation and start-stop cycles. The oscillations were nearly three times higher than that of the normal operating conditions. The literature indicated that the repeated transients affect the operating life of the turbine components. 16-19 During a transient condition, the turbine passes through a rapid pressure variation and experiences low-cycle fatigue. 20,21 The repeated fatigue loading to the runner blades initiate cracks where the blades are welded. 22 Pressure pulsations developed in a draft tube are primarily related to the vortex breakdown. The pressure pulsations are composed of two different phenomena that occur simultaneously at the same frequency, which may be synchronous (axial) and asynchronous (radial) types. 23,24 The synchronous component may have equal phase and amplitude in the runner and the draft tube. The pressure may be considered as a plane wave propagating to the hydraulic system through the draft tube. The asynchronous component is a pressure pattern that develops at the runner downstream and that rotates about the circumference of the draft tube. The rotation period is dependent on the circumference and the runner angular speed. The synchronous component may not be present at high load conditions. In a straight/conical draft tube, only asynchronous type pulsations exist. 25 Both synchronous and asynchronous types of pressure pulsations cause different impacts on turbine operation. It is important to analyze and distinguish such pulsations properly. During the steady-state operating condition of a turbine, the pulsations are periodic and may repeat over certain periods of time. 26-29 However, during load variation and start-stop, the pressure pulsations are non-repeating and largely dependent on the runner's instantaneous speed as well as guide vanes' apertures at that time. Recently, velocity measurement conducted by Goyal et al. 30,31 indicated that the vortex structure in the draft tube evolves over a certain time as the runner accelerates/decelerates. The study showed that, unlike a steady-state load, 32-35 amplitudes of both types of pressure pulsations vary with time as the load changes from one operating point to another. The frequency of synchronous pulsations appeared before the asynchronous pulsations during...

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Section: -13mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of the unsteady pressure pulsations in the prototype Francis turbines during load variation and startup

Trivedi

Gogstad

Dahlhaug

2017

Journal of Renewable and Sustainable Energy

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“…•Load change: During the transition from one steady operating condition to another and in order to generate more or less power depending the operator desire, the flow rate passing through the machine is modified by moving the wicket gates. Some references [85] state that this transi tion can be neglected in terms of fatigue analysis and do not consider it [68,81], while some reviews show the importance of take it into account [86].…”

Section: Static Stresses Characteristic Influence Of Head and Loadmentioning

confidence: 99%

“…The acceleration of the unit until its nominal speed is one of the critical operating conditions [57,68,85,88]. Due to its damaging characteristics, in the last years, a lot of research has been performed in the optimization of the start-up process, which can decrease notably the static and dynamic stresses during this transient phenomena [57,68,85,86,89].…”

Section: Start Upmentioning

confidence: 99%

Fatigue life estimation of Francis turbines based on experimental strain measurements: Review of the actual data and future trends

Presas

Luo

Wang

et al. 2019

Renewable and Sustainable Energy Reviews

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Due to the massive entrance of new renewable energies such as wind or solar, hydraulic turbines have to work far from its designed point and withstanding multiple transients, such as starts and stops, that shorten the useful life of the machine and cause fatigue damages. The present paper reviews the complex problem of fatigue in Francis turbines particularly focused on the experimental data available for static and dynamic stresses. For this purpose, many researches, which include different Francis turbines covering a wide range of design head and power, have been considered. The experimental stresses characteristics measured with strain gauges installed on the turbine runner and obtained from previous works have been analyzed for the different operating conditions and transient states occurring in the normal life of actual Francis units. The actual computational capabilities and techniques typically used to estimate such stresses have been discussed in detail. Potential future techniques to simplify complex strain measurements on the turbine runner, computational and statistical methods to estimate turbine stresses are reviewed in this paper. Finally, the relative damage of the different operating conditions and useful life estimation of the turbine, based on past strain measurements of the runner, are addressed.

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“…Since deep part load could be eliminated as a source of those cracks, it was assumed that either start-up, shutdown or some unknown phenomena lead to the cracks. From recent literature (Gagnon et al [5] & [6]), it is assumed that the start-up process can be responsible for the observed kind of cracks. To get more information, extensive measurements have been performed on the Group 2 of the power plant.…”

Section: Introductionmentioning

confidence: 99%

On-board measurements at a 100 MW high-head Francis turbine

Ttizschkau¹,

Hasmatuchi²,

Decaix³

et al. 2019

Wasserwirtsch

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The Francis turbine runners of the four ternary groups of Grimsel 2 power plant in Switzerland showed fatigue cracks at the runner blades much earlier than expected. To find the source of these cracks, strain gauges and accelerometers were used to get information about the harmful stresses on the runner during operation. It is observed that the speed no-load operation during the start-up and the shutdown processes of the turbine impose large stresses on the runner blades.

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A look at Francis runner blades response during transients

Cited by 22 publications

References 2 publications

Investigation of the unsteady pressure pulsations in the prototype Francis turbines during load variation and startup

Investigation of the unsteady pressure pulsations in the prototype Francis turbines during load variation and startup

Fatigue life estimation of Francis turbines based on experimental strain measurements: Review of the actual data and future trends

On-board measurements at a 100 MW high-head Francis turbine

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