Empirical findings on the transmission of draft tube instabilities along the penstocks of hydraulic plants

29th IAHR Symposium on Hydraulic Machinery and Systems

Héraud, Jean^1 ; Lecomte, Bruno^2 ; Comelli, Mathieu^3 ; Lowys, Pierre-Yves^4 ; Pavic, Goran^5

Hydromechanics Engineer, EDF DTG MPSH, 21 Av. Europe, Grenoble

38040, France^1

Senior Engineer, EDF DTG MPSH, 21 Av. Europe, Grenoble

38040, France^2

Hydromechanics Engineer, GE Renewable Energy Hydro Solutions, Hydromechanics COE, Avenue Léon Blum, BP 75, Grenoble

82, 38041, France^3

Senior Consulting Engineer, Dynamic Systems, GE Renewable Energy Hydro Solutions, Avenue Léon Blum, BP 75, Grenoble

82, 38041, France^4

LVA, INSA de Lyon, Villeurbanne

69621, France^5

关键词: Dynamic pressures;    Empirical findings;    Frequency ratios;    Mechanical fatigue;    Pressure fluctuation;    Pressure oscillation;    Production plant;    Statistical approach;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/240/5/052034/pdf
DOI  :  10.1088/1755-1315/240/5/052034

来源: IOP

【 摘 要 】

On EDF hydraulic production plants equipped with Francis turbines, there have been related some cases of significant pressure fluctuations detected in the upper parts of the penstock when units were operating in the high load pressure surge zone. There was no decrease of the Peak-to-Peak pressure fluctuations along the penstock in the upstream part as it could be expected. To understand the phenomenon, on site tests have been carried out using innovative non-intrusive dynamic pressure sensors in many points along the penstock allowing the analysis of upward and downward waves and their "interferences". These interferences cause in some cases standing waves for which the envelope of pressure oscillations along the penstock exhibits nodes and anti-nodes whose positions are relatively fixed along the penstock for a given operating point of the turbine. It appears that the ratio [Frequency of surge]/[Natural frequency of the penstock] conditions directly the number of nodes. This point is important because upper zones of the penstock close to the surge tank have generally not been designed to withstand high values of pressure fluctuations. For high number of ratio (3, 5, 7...), long term operation may induce mechanical fatigue of the penstock. A statistical approach was performed based on the dynamic signal databases of EDF and GE comprising data analysis of 21 occurrences of strong axial pressure surges of high load. It seems that certain values of the frequency ratio favour this resonance. This emphasizes the role of water exchanges between the rope and the penstock (complementarily with the draft tube) in establishing the conditions of resonance.