Water column separation under one-after-another load rejection in pumped storage station

Abstract

A pumped storage power station operates on the principal of multiple pump-turbines sharing one tunnel. However, safety is a concern, particularly under one-after-another load rejection of multiple pump-turbines. In this study, we have implemented a model experiment based on water column separation experiment under the condition of one-after-another load rejection of a pumped storage model experimental platform with two pump-turbines sharing one tunnel. The results show that the unit with water column separation, which is Unit # 2, has the worst moment when it rejects full load 0.8 s after Unit #1. At this condition, the wall pressure of the draft tube of unit # 2 attains the vapor pressure and reverse water hammer pressure attains the maximum value of 6.8 m during water column bridging. However, the reverse water hammer pressure was 290 m in prototype unit. Under one-after-another load rejection, water column separation occurs when the draft tube attains the second extreme value, and the unit located in the turbine braking condition area. It was observed that the pressure pulsation frequency of the draft tube after one-after-another load rejection is composed of two parts. First, pressure pulsation frequency caused by swirling flow with a value of 0.4 f/fn and second, a broadband of 40–200 Hz generated by the reverse water hammer due to water column bridging and structural response of the unit.