Transient characteristics of PAT in micro pumped hydro energy storage during abnormal shutdown process

Abstract

Pumps as turbines play an important role in micro pumped hydro energy storage (PHES) systems, which are widely applied in remote areas, and their operational safety can be significantly affected by the transient power-off process. The aim is to analyze the unsteady internal flow characteristics and time–frequency characteristics of the pressure fluctuations of the pump as turbine (PAT) after power-off process by using finite volume method (ANSYS CFX) and bidirectional test rig. During the transient process of power failure, internal flow instabilities were revealed by analyzing the flow field and turbulence kinetic energy. The results indicated that the flow field between the blades was extremely unstable during the brake mode. Additionally, the absolute values of the rotational velocity and flow rate were 1.21 and 0.93 times higher than the initial values, respectively, during the runaway mode. The pressure fluctuations were analyzed in the time-frequency domains using the continuous wavelet transform. The main frequency of pressure pulsation at the volute was related to the rotating speed owing to the rotor-stator interaction. This study revealed the transient flow features during the process of mixed-flow pump as turbine failure, which provides a fundamental theory for the safe transient operations of pump as turbine.