PSI - Issue 5

Jaroslav Václavík et al. / Procedia Structural Integrity 5 (2017) 1349–1354 Jaroslav Václavík et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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The other task is to track the signal for finding of dynamic torsional impact events, which are characterized with peaks and following damped oscillations. These events are included in signal statistics and rainflow matrices. However, the resonance frequencies of the whole system are excited in these short intervals, which are not visible during stationary conditions. Therefore for each impact event and also for daily record the amplitude spectrograms are evaluated and stored. The final task is the evaluation of daily two-parametric histograms of torsional vibration amplitudes using rain flow method. These matrices are stored in daily files for further processing. Daily reports are generated automatically obtaining all evaluated data, and transferred through the LAN interface to the host computer. The daily files are further pos-processed to view the trends in torsional signal, the fatigue accumulation damage or the development of excited resonance frequencies. An example of captured torsional vibration response to electrical line fault is shown in Fig. 6 together with the spectrogram of this event. Several excited resonance frequencies are visible just in the moment of the response for a few seconds. These types of charts are included in each daily report. The time history of minimum and maximum values of torsional moment is presented in Fig. 7 for several years. Here, all non-standard events including long-term cuts off of the electric power system are good visible. The distribution of registered fault responses for four years of torque monitoring is shown in Fig. 8a. In Fig. 8b, the one-parametric rain-flow matrix is demonstrated for the same of time period. Here, the torque amplitudes are also recalculated to sheer stress amplitude in the cut of strain gauge positions in the shaft. In Fig. 9, an example of amplitude spectra and the spectrogram, obtained during shut down the turbine generator is demonstrated. Our effort is to find the blade responses in the spectrograms and track their frequency changes. 4. Results overview

Fig. 6. Example of torsional response to line fault a) time history; (b) spectrogram of the event.

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Fig. 7. Time history extremes of the monitored torque during three years