The highest vibration levels in large pump turbines are, in general, originated in the rotor stator interaction (RSI). This vibration has specific characteristics that can be clearly observed in the frequency domain: harmonics of the moving blade passing frequency and a particular relationship among their amplitudes. It is valuable for the design and condition monitoring to count on these characteristics. A CFD model is an appropriate tool to determine the force and its characteristics. However, it is time consuming and needs highly qualified human resources while usually these results are needed immediately and in situ. Then, it is useful to determine these characteristics in a simple, quick, and accurate method. At present, the most suitable method indicates a large amount of possible harmonics to appear, without indicating the relative importance of them. This paper carries out a theoretical analysis to predict and explain in a qualitative way these frequencies and amplitudes. The theoretical analysis incorporates the number of blades, the number of guide vanes, the RSI nonuniform fluid force, and the sequence of interaction. This analysis is compared with the method currently in use, and both methods are applied to a practical case. The theoretical analysis gives a resulting force over the pump turbine, which corresponds well to the measured behavior of a pump turbine in terms of its frequencies and the relationship between their amplitudes. A corrective action is proposed as a result of the analysis and after it is carried out in one of the units, the vibration levels are reduced. The vibration induced by the RSI is predicted considering the sequence of interaction and different amplitudes in the interactions between the same moving blade and different stationary blades, giving a different and original interpretation about the source of the vibration characteristics. A successful corrective action is proposed as a consequence of this new interpretation.

At present, pumped storage is the only system to store huge amounts of energy. The surplus of energy in the electrical grid is used for pumping water from a lower to a higher reservoir (pump operation). At peak hours or in case of emergency this water goes down generating electrical energy (turbine operation). In the last years, due to the massive entrance of wind power, the number of start and stop cycles have increased dramatically as well as the operation at very low loads. In this new scenario more cases of damage have been reported and an effective vibration monitoring is necessary.\ud \ud Reversible pump-turbines (RPT) are high performance machines that have to change operation from pump to turbine mode (reversing runner rotation and flow direction) in a short time. Due to their special design characteristics (large power concentration) and operating conditions, they generate large pressure pulsations and forces when in operation.\ud In this paper the vibration monitoring of large RPT units have been analysed. The results obtained after 15 years of monitoring several power plants with this type of machines have been used for the analysis. In the last years, most of the supervised power plants have been monitored on-line remotely.\ud First the monitoring system used is described. The main types of excitation forces expected during the operation of these machines are studied especially the most characteristic and distinctive that are the pressure pulsations due to the rotor/stator interaction.\ud The vibration signatures measured in machines with different designs are analysed in detail and compared with the signatures of conventional turbines. The influence of the operation type (as a pump and or as a turbine) and on the power delivered has been studied and the changes of the signatures presented. After the analysis of the vibration signatures the procedure used for the selection of spectral bands is explained.\ud \ud The analysis of the results obtained with the monitoring is shown. First the evolution of overall levels and the comparison with vibration Standards is discussed. Second the main types of damage found are introduced. Damage in the generator, in bearings, in supporting structure and abnormal operation with cavitation are shown. The changes in vibration signatures and spectral bands for these types of damage are also given. Finally the specific case of damage in runners is introduced.Postprint (author's final draft

Spectral vibration analysis using the Fourier transform is the most common technique for evaluating the mechanical condition of machinery working in stationary regimen. However, machinery operating in transient modes, such as variable speed equipment, generates spectra with distinct frequency content at each time, and the standard approach is not directly applicable for diagnostic. The "order tracking" technique is a suitable tool for analyzing variable speed machines. We have studied the computed order tracking (COT), and a new computed procedure is proposed for solving the indeterminate results generated by the traditional method at constant speed. The effect on the accuracy of the assumptions inherent in the COT was assessed using data from various simulations. The use of these simulations allowed us to determine the effect on the overall true accuracy of the method of different user‐defined factors: the signal and tachometric pulse sampling frequency, the method of amplitude interpolation, and the number of tachometric pulses per revolution. Tests on real data measured on the main transmissions of a mining shovel were carried out, and we concluded that the new method is appropriate for the condition monitoring of this type of machine.