To determine the source of oscillations a continuous vibration monitoring is required. Many of these causes, as in the case of cracks, are recognized by existing monitoring systems as deviations from the normal operating state only if it is already too late. The reason is the frequency range analyses currently integrated in existing Condition Monitoring Systems. For example, the amplitude and frequency variations within one shaft revolution characteristic of fracture formation are lost by averaging in Fast-Fourier-Transformation.
Methods in the area of signal analysis
In the recent past, signal analysis algorithms have been developed for non-linear and non-stationary vibrations which allow computation of the frequency domain information in each measurement step. This process facilitates the detection of breathing cracks, particularly in the transient operating state.
The improved time resolution of the frequency spectrum, however, is not sufficient to detect the crack because no unambiguous criterion for fracture detection yet exists. Rather, a classification problem for an extensive feature vector has to be solved: one separates the cracks from other structural effects.
A department of Uniper Anlagenservice provides services in the field of vibration monitoring on power plant turbines. We developed a software tool for the automatic detection of cracks on the basis of a conceptual analysis of the latest methods from the fields of signal analysis and crack classification.