Identification of instantaneous attributes of torsional shaft signals using the Hilbert transform

A systematic analytical procedure based on the concept of the analytic signal (AS) of Gabor is used to determine the time-varying attributes of torsional oscillations, namely the instantaneous amplitude and the instantaneous frequency. Methods for implementing the AS using the numeric Hilbert transform are given and criteria for characterizing nonlinear effects are discussed. The proposed methodology is demonstrated on the IEEE First Benchmark Model (FBM) for subsynchronous resonance studies. The AS analysis is performed on output data files generated by nonlinear simulations using the EMTP, but the method is general and is applicable to any nonlinear, nonstationary signal. Numerical results include the determination of the instantaneous frequency of torsional oscillation signals following large perturbations. Comparison of numerical results obtained by the proposed method with linear analysis techniques is provided.