Load Rejection Test and Numerical Prediction of Critical Load Case Scenarios for Pumped Storage Plant

A pumped storage plant (PSP) is by far the most cost effective and mature technology for energy storage at a large-scale, and therefore, this technology is rapidly being developed and deployed. A reversible pump turbine (RPT) is the vital component of a PSP, and whether a PSP can operate safely and stably mainly depends on the characteristics of the RPT. However, the existence of S-shaped characteristics of a RPT usually leads to severe water hammer and pressure pulsations during the transient processes of load rejection. Therefore, hydraulic transient analysis in a PSP is one of the most important issues for the prevention of undesirable pressure fluctuations in waterways. Theoretically, the most accurate method is to conduct on-site measurements of all possible load cases to obtain the extreme values of pressure. However, extreme operating conditions such as 2-stage load rejection pose serious threats to the safety of the water conveyance system, making it impossible to carry out field trials under such conditions. This paper gives the numerical prediction of extreme and critical load case scenarios from the simultaneous load rejection field test on a double unit of a PSP in China. The dynamic transient numerical model for load rejection of the PSP is developed by introducing the method of characteristics. The boundary conditions, such as the real adopted wicket gate closure law and parameters of the water conveyance system, are calibrated according to the field test data. Considering the large pressure pulsations in the PSP during load rejection, a proper pressure pulsations amendment is proposed as well. Eventually, the hydraulic behavior of the critical load cases are numerically investigated by the modified model. And the results are amended by the proposed pressure pulsations processing approach to predict whether the hydraulic parameters can satisfy the design criteria, which can ensure safe operation of the PSP in the future. The achievements of the study can serve as a reference for similar PSP projects.