Abstract: Based on the one-dimensional transient flow theory and the method of characteristics, two mathematical models, one for simulating the surge tank and the other for the pressure reducing valve, are developed and applied to a hydropower station with a long distance diversion pipeline. We simulate and compare the combination scheme of a single surge shaft and a pressure reducing valve with the scheme of a single surge shaft, considering the working principle of the surge shaft and the pressure valve and the control requirements of limiting the unit speed increasing rate and volute end peak pressure during the load rejection of all the units. It reveals that the combination scheme can reduce these two controlled factors significantly and effectively. In addition, we analyze the operation safety of the station adopting different types of pressure reducing valves, and determine the opening and closing rules of the valve and the principle of valve diameter selection.

Key words: hydropower station, protective measures, surge shaft, pressure reducing valve, valve diameter, opening and closing rules