CASE STUDY OF OPERATIONAL MODAL ANALYSIS (OMA) OF A LARGE HYDROELECTRIC GENERATOR

In the context of a study of existing generators ’ power increase, full instrumentation was installed on several high-power hydro-generators (> 60 MW). Some vibration measurement and analysis bases on FFT analysis were presented last year at CMVA annual symposium [1]. These results also included the measurements of the Operating Deflection Shape (ODS) to illustrate the dynamic motion of the stator during operation of the hydro-generator unit. This presentation will focus on the Operational Modal Analysis (OMA) of a high-power hydroelectric generator using a vector autoregressive ARMA model, employed in a short time manner in order to identify and survey the monitoring of excitation frequencies and modal parameters. A mode classification technique is developed for the discrimination of the most excited electromagnetic harmonics from natural frequencies and spurious modes. This discrimination allows for the monitoring of close modes, the frequency response function spectrum and of the operating deformation shapes due to electromagnetic excitations. The conclusion of these temporal analyses will be compared with standard FFT spectrum analysis