Feasibility of on board measurements for predictive maintenance in large hydraulic turbomachinery

Resumen

To progressively introduce predictive maintenance in large hydraulic turbomachinery (LHT) it is necessary to improve its vibration condition monitoring. The runner of the LHT is one of the elements more prone to suffer a critical failure. For that reason, the detection of its excitations is fundamental. Pump-turbines are a special type of LHT that work with higher heads than other LHT. Because of its design and operating conditions, the hydraulic interference between the moving runner blades and the fixed guide vanes (rotor-stator interaction RSI), generates large excitation forces at the blade passing frequency and its harmonics. These excitations act on the runner which may suffer large stresses and fatigue damage. At present, this fact limits the maximum head per stage what makes this topic of high interest for its design. For standard combinations of number of blades and guide vanes, the maximum amplitude in the RSI occurs normally at the second or third harmonic of the blade passing frequency which makes the RSI prone to produce resonance in the runner and nearby structures. At the moment it is not possible to calculate with precision the relative amplitude of the harmonics found in the RSI. It is neither possible to determine with accuracy the natural frequencies of the runner submerged in water. Therefore, there are uncertainties to determine the vibratory behavior of the runner and the rest of the LHT. The general objective of this thesis is to improve the condition monitoring based in vibration analysis in pump-turbines. In particular it is wanted to improve the detection of the excitations on the runner (especially the RSI). The first is to check the feasibility of using a new measuring position closer to the runner: the shaft (rotating reference).