Experimental study of a Francis turbine under variable-speed and discharge conditions

Trivedi, Chirag; Agnalt, Einar; Dahlhaug, Ole Gunnar

doi:10.1016/j.renene.2017.12.040

Cited by 48 publications

(16 citation statements)

References 47 publications

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“…The Francis test-rig available at the Waterpower laboratory, Norwegian University of Science and Technology was used for the experimental studies [22]. The Francis test-rig was equipped with all required instruments to conduct model testing according to IEC 60193 [23].…”

Section: Methodsmentioning

confidence: 99%

The Rotor-Stator Interaction Onboard A Low Specific Speed Francis Turbine

Agnalt

Solemslie

Storli

et al. 2020

IJFMS

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Over the last years, several breakdowns in hydropower plants with low specific speed Francis runners have been reported. One of the main excitation forces in such runners is the pressure fluctuations originating from the rotor stator interaction. In this paper, the rotor-stator interaction has been analyzed utilizing pressure sensors onboard the runner. The pressure sensors were flush mounted in the hub of the runner and the signals were transmitted through a slip-ring system. The measurements have been analyzed relative to the runner angular position by utilizing an angular position sensor mounted to the shaft end. Measurements with different guide vane angle have been compared in order to study the potential flow interaction and the viscous wake effects for the pressure inside the runner. The results from the onboard pressure measurements found that the phase of the guide vane passing pressure seen by the onboard pressure sensors was independent of the guide vane opening. Hence, the potential flow interaction was found to be the dominant effect and no evidence from the viscous wake effect was found on the onboard pressure.

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Section: Methodsmentioning

confidence: 99%

The Rotor-Stator Interaction Onboard A Low Specific Speed Francis Turbine

Agnalt

Solemslie

Storli

et al. 2020

IJFMS

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“…The modeled turbine includes spiral casing with 14 stay vanes, 28 guide vanes, a runner with 17 blades and the elbow type draft tube. Detailed description of the test facility is presented in a previous publication [16]. Table 1 describes the boundary conditions and the numerical parameters enabled for the simulations.…”

Section: Test Casementioning

confidence: 99%

Numerical Study of a Francis Turbine over Wide Operating Range: Some Practical Aspects of Verification

2020

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Hydropower plays an essential role in maintaining energy flexibility. Modern designs focus on sustainability and robustness using different numerical tools. Automatic optimization of the turbines is widely used, including low, mini and micro head turbines. The numerical techniques are not always foolproof in the absence of experimental data, and hence accurate verification is a key component of automatic optimization processes. This work aims to investigate the newly designed Francis runner for flexible operation. Unsteady simulations at 80 operating points of the turbine were conducted. The numerical model consisted of 16 million nodes of hexahedral mesh. A SAS-SST (scale adaptive simulation-shear stress transport) model was enabled for resolving/modeling the turbulent flow. The selected time-step size was equivalent to one-degree angular rotation of the runner. Global parameters, such as efficiency, torque, head and flow rate were considered for proper verification and validation. (1) A complete hill diagram of the turbine was prepared and verified with the reference case. (2) The relative error in hydraulic efficiency was computed and the over trend was studied. This allowed us to investigate the consistency of the numerical model under extreme operating conditions, far away from the best efficiency point. (3) Unsteady fluctuations of runner output torque were studied to identify unstable regions and magnitude of torque oscillations.

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“…It has higher efficiency than alternative approaches and lower operating costs. Moreover, it can help to improve dynamic stability of the turbine at off-design condition [9]. The cavitation effect can be mitigated and the drive train can be simplified more.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Evaluation of loss effect on optimum operation of variable speed micro-hydropower energy conversion systems

et al. 2019

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This paper evaluates the effect of converter and generator losses on the maximum power point (MPP) of variable speed micro-hydropower energy conversion systems. As a case study, a semi-Kaplan micro-hydropower turbine with a permanent magnet (PM) generator and a back-to-back full converter is considered. Using the analytical model, different loss terms, such as converter losses, PM generator losses and mechanical losses are calculated at different shaft speeds. Then, the curves of turbine power and injected power to the grid are extracted as a function of turbine speed. It is shown that the maximum attainable power of the variable-speed hydropower system does not correspond to the MPP of hydraulic turbine. In other words, to get the maximum power from the whole hydropower system, it is necessary to consider power losses of the electric generator and power electronic interface between the turbine and the grid. These power losses can change the power-speed characteristics or MPP location of the hydropower system. According to this fact, the conventional MPP tracking (MPPT) algorithms which try to track the MPP of hydraulic turbines fail to extract the maximum power. Hence, a modified perturb and observe (P&O) MPP tracking algorithm is proposed for the variable speed hydropower systems to increase their efficiency. The modified tracking algorithm finds the "optimum MPP" automatically and without the extra calculations. Also, the injected power to the grid is increased 3.7% when the modified algorithm is applied to the studied case study. Finally, the validity of theoretical claims is verified by experimental tests on a 5 kW hardware prototype.

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Experimental study of a Francis turbine under variable-speed and discharge conditions

Cited by 48 publications

References 47 publications

The Rotor-Stator Interaction Onboard A Low Specific Speed Francis Turbine

The Rotor-Stator Interaction Onboard A Low Specific Speed Francis Turbine

Numerical Study of a Francis Turbine over Wide Operating Range: Some Practical Aspects of Verification

Evaluation of loss effect on optimum operation of variable speed micro-hydropower energy conversion systems

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