Abstract
Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.
Highlights
The results show that the transient characteristics of the cavitation are more complicated than the results of an ordinary steady-state cavitation calculation when cavitation occurs in the transient process, because the transient process will pass through many operating regions in a short time
The unit be stable in no-load operation, which a load rejection propulsations, the unit will will be stable in no-load operation, which is a is load rejection process
During the rejection load rejection process, the minimum pressure the draft tube is inlet is During the load process, the minimum pressure in theindraft tube inlet most most to occur the speed maximum moment, in the which the cavitation is present
Summary
Different from conventional power and pumping stations, a pumped-storage power station has a long water conveyance system, which means the transition process’s effect on the flow in the pump-turbine is more significant. The field test results show that there is a significant amount of pressure pulsations at the draft tube during the transition process [1,2]. Some power stations even suffer from structural damage due to severe unit vibration [3]. Luo X. et al [4] calculated and analyzed the runaway transient process of a tubular turbine, and found that a strong pressure pulsation was generated in the draft tube, at up to 104% of the test head, which threatened the safe and stable operation of the unit.
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