Analysis of transient pressure of pump-turbine during load rejection based on a multi-step extraction method

During the load rejection condition of the pump -turbines, the S-shaped characteristic would lead to intense pressure pulsations, thus threatening the safe operation of the pumped storage plants (PSPs). Extracting water harmer pressure (WHP) and pulsating pressure (PP) from the measured pressure signals is of great engineering significance. As a result, this study proposes a novel multi -step extraction framework for the WHP. First, a theoretical method for extracting WHP is developed by analyzing the transient properties of the pressure pulsations. Subsequently, a denoising strategy combining improved variational mode decomposition (IVMD) and multi -level wavelet denoising (MWD) is presented to reduce noise interference. The proposed IVMD is used to reduce wideband noise, and the MWD method is developed to reduce narrow -band noise within the IVMD decompositions. Finally, the proposed method's effectiveness is verified using spiral case inlet and draft tube inlet pressure signals acquired from a prototype pump -turbine of 375 MW. The results show that the proposed denoising method can effectively reduce noise interference and accurately extract WHP. This study provides an innovative and theoretically -based method for extracting WHP and PP, which has important engineering significance for the safe operation of PSPs.