Abstract
The transient process in the hydropower station with both surge tank and pressure regulating valve is quite complicated and also critical to operation safety. According to the pressure regulating valve working principle, the influence of the valve diameter on the unit speed and spiral case pressure was analyzed theoretically. Mathematical models of the surge tank and pressure regulating valve in the hydropower station were established based on the characteristic method. In a practical engineering, numerical simulation of large fluctuation and hydraulic disturbance transient process are conducted, verifying the correctness of the theoretical analysis. Based on the calculation results, three principles for selecting the valve diameter are concluded: first, making sure the unit speed meet the regulating guarantee requirements when guide vanes fast close; second, the maximum spiral case pressure of two times should be approximate to each other by controlling the superposition of surge wave and water hammer; third, the maximum flow of the valve should be as close to the rated flow of the turbine as possible. The principles are helpful for selecting the valve diameter in similar hydropower station.
Highlights
Load rejection transient process is a frequent occurrence in hydropower station
The transient process of hydropower stations with pressure regulating valves (PRV) instead of surge tank (ST) have been studied by many scholars, so empirical formula is available for the diameter selection of PRV [9]
The PRV commonly used in China is the TFW type, whose working principle is: when the unit load increases or remains unchanged, or the load rejection is less than 15% of the rated output, it stays closed; when the instant load rejection is more than 15% of the rated output, it fast opens to discharge flow, and slowly closes when the guide vanes are completely closed [13]
Summary
Load rejection transient process is a frequent occurrence in hydropower station. During the process, to control the unit speed, the guide vanes will close rapidly, which will cause large water hammer pressure in pipelines, threatening the safe operation of the station [1,2,3]. A big ST is hard to excavate because of the difficulty in technology and capital The transient process of hydropower stations with PRV instead of ST have been studied by many scholars, so empirical formula is available for the diameter selection of PRV [9]. The influence of PRV diameter on Hmax,s, Nmax,u, and the maximum rising rate of unit torque (Tmax,u) were analyzed theoretically in the load rejection transient process of the hydropower station with both ST and PRV. Based on the theoretical analysis and numerical simulation results, three principles for selecting the PRV diameter were summarized
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