One of the most important procedures in evaluating the operational stability of a hydro unit is vibration measurement and analyses. The most important conclusion lies in the identification of permanent changes in the state as well as the determination of the type and location of changes. Any change in vibrational state can be related to the changes in the unit’s construction properties (bearing, stator, bracket/foundation stiffnesses and vibrating masses of rotating/non-rotating construction elements). Identification of these properties shows that they are very often different for a real hydro unit when compared to the designed properties. A procedure was developed based on which a hydro unit’s properties can be determined without the use of design data. In order to carry out the identification procedure it is necessary to conduct vibration measurements and analyses on all the bearings simultaneously. The results of the procedure are the oil film stiffness, stator stiffness, bracket/foundation stiffness, shaft stiffness and critical speeds.
As an example of the implementation of this procedure a reversible 180 MW hydro unit was used for which the bearing stiffnesses change significantly with thermal state (that is, stator and rotor thermal dilatations). Apart from the identification of the unit component’s stiffnesses, a procedure for the first critical speed (cold and hot) was conducted. The results have shown that the calculated parameters from measured data compared to the design parameters are significantly different. For this reason there are significant vibrational problems in the operating regimes for which unexpected resonance states occur. The identification procedure can be performed with post processed data (stored waveform/trends data) originating from multi-channel measurement devices/analyzers and can also be embedded into the continuous on-line diagnostic monitoring systems for real time monitoring.