Application of stationary wavelet packets decomposition based hilbert spectrum to nonstationary hydraulic turbine vibration signal analysis

The multi-band decomposition based on stationary wavelet packets transform avoids the defects inherent with Hilbert-Huang transform, such as the pseudo mode functions from empirical mode decomposition and the instantaneous frequency ripple of relatively high frequency intrinsic mode functions. The modification of Hilbert spectrum via stationary wavelet packets decomposition improves its resolution in analyzing the high frequency wide band signals, and enables it more suitable to process the complicated multi-component nonstationary signals. It is employed to analyze the nonstationary vibration signal of a hydroturbine during the shut-down and start-up transient processes. It is found that the main shaft vibration is mainly composed of the rotating frequency and its harmonics, and the rotating frequency is dominant. The comparison with Hilbert-Huang transform verifies its feasibility and effectiveness in analyzing the nonstationary vibration signals of hydroturbine during transient processes.