The paper studies the hydraulic-mechanical coupling vibration (HMCV) performance of pumped storage power station (PSPS) with two turbine units sharing one tunnel (TTUSOT) based on overall transfer matrix. Firstly, the model of PSPS with TTUSOT is established by overall transfer matrix method. The overall transfer matrix is derived. Then, the effects of hydraulic parameters and mechanical parameters on vibration performance are analyzed. Finally, the HMCV performance under three operating conditions is studied. The results show that the HMCV is superposed by the nine orders of vibrations. The hydraulic parameters and mechanical parameters can affect specific orders of vibrations and change the stability. In overlapping interval, one value of surge tank area corresponds to two values of the 1st order of vibration. The operating condition affects the stable domain by changing the 2nd order of attenuation factor. When the 2nd order of attenuation factor increases from negative to positive with the increase of integral gain of governor, the stability of PSPS changes from stable to unstable. When the load changes are undertaken by two turbine units simultaneously, the situation of equal distribution of load changes has a better stability than that of unequal distribution of load changes. • Model of PSPS with TTUSOT is established by transfer matrix method. • Overall transfer matrix of PSPS with TTUSOT is derived. • Effects of hydraulic and mechanical parameters on vibration are revealed. • HMCV performance of PSPS under three conditions is studied. 

Hydraulic-mechanical coupling vibration performance of pumped storage power station with two turbine units sharing one tunnel

Hydraulic coupling vibration characteristics and control of hydropower station with upstream and downstream surge tanks

Vibrations are one of the major issues observed during the operations of Francis turbine as they are frequently operated outside their optimal operating range, with rapid load changes. In hydropower plants, vibrations occur in various parts which can be classified as: hydraulic civil parts such as reservoir, intake, dam, tail race etc. mechanical parts such as penstock, turbine, draft tube and shaft, and electrical parts such as generator and transformer. However, due to the sediments and cavitation problems, the regions around rotating parts such as turbine experiences severe vibration. In the cases where the turbines need to be operated with high sediment load, the vibration problems could be further aggravated due to sediment carrying flow and declination of the surface morphology after erosion. This paper is based on a literature review to explore the characteristic effects of erosion and cavitation which could result in losses, vibrations, fatigues on the turbine materials and oblivious turbine failure. The study aims to correlate the erosion and cavitation due to abrasion with the pressure fluctuations resulting in vibrations.

A review on erosion and erosion induced vibrations in Francis turbine

Vibration Fault Analysis of Hydropower Units Based on Extreme Learning Machine Optimized by Improved Sparrow Search Algorithm

Hydraulic vibration is a critical factor affecting the stability and health of the hydro-turbine generator unit (HGU). This paper investigates the nonlinear dynamic characteristics of the HGU occurring from the hydraulic vibration. First, using the turbulence flow model, the lift and drag coefficients of the asymmetric airfoil blades are calculated at different Reynolds numbers and angles of attack. Based on the lift and drag coefficients of the asymmetric airfoil blade, a novel nonlinear mathematical model of asymmetric hydraulic forces is proposed for the asymmetric airfoil blade. Then, combining mechanic and electric asymmetric excitations, a coupled nonlinear mathematical model of the HGU is built using Lagrange equations. Moreover, the correctness of this model is verified. Finally, dynamic behaviors of the HGU changing with attack angle, deviation of the outlet blade angle, outlet guide vane angle, and Reynolds number are analyzed by bifurcation diagrams. It is found that increasing the Reynolds number can enhance the hydraulic vibration, which can lead to more complex nonlinear bifurcation and chaotic motions. In addition, some interesting physical phenomena of HGU under critical ranges and values are obtained. More importantly, these results could give theoretical guidance in the designing and stability research of hydropower units.

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Nonlinear Hydraulic Vibration Modeling and Dynamic Analysis of Hydro-Turbine Generator Unit with Multiple Faults

To understand the hydraulic vibration characteristics in a traditional hydropower system and identify possible exciting sources that may induce serious hydraulic vibrations in the flow passage, experimental tests and numerical calculations were conducted for different operating conditions. The experimental results show that the pressure fluctuations are mainly related to the vortex rope phenomena in the draft tube, and the dominant frequency of pressure fluctuation is 0.2~0.4 times the runner rotational frequency (fn). The numerical results show all the attenuating factors are negative, which indicates the system itself is stable on the condition that all the hydraulic elements have steady operating performance. The free vibration analyses confirm that the frequency range of the vortex rope in the draft tube partly overlaps the natural frequencies of the hydropower system. Apart from the vortex rope, the runner rotational frequency is another common frequency that is approximately equal to the frequency of the 10th vibration mode. From the vibration mode shapes, it is inferred that a small disturbance in its frequency close or equal to a specific natural frequency of the vibration mode could induce large pressure oscillations in the tail tunnel. In light of the system’s response to different forcing frequencies, the vortex rope formed under off-design conditions and runner rotational frequency is verified to be the potential exciting source of a traditional hydropower system, and the frequency 0.2 fn is much more dangerous than other disturbances to the system.

Fei Yang

Papers

Hydraulic Vibration and Possible Exciting Sources Analysis in a Hydropower System