Transient analysis to air chamber and orifice surge tanks in a hydroelectric generating system during the successive load rejection

Abstract

Surge tank is an essential device to control hydraulic transient of a Hydroelectric Gnerating Systems (HGS)s. However, various types of surge tanks differently reflect in reducing water hammer and improve performance of HGS. This study aims to analyze the different performance of Air Chamber Tank (ACT) and Orifice Surge Tank (OST) during the successive load rejection process (SULRP). In this study, the mathematical model of the ACT is established and use to analysing the replacement the existing OST in Shitouxia Hydropower station consisting in three parallel unit system.A modified NSGA-II algorithm is used to perform multiple objective optimization ACT properties and to minimize pressure head in ACT and water head at the inlet of units. The optimization result indicates that the proper selection of initial indoor air height and delay time lead to the decrease maximum water head and fluctuation period in surge tank and falls in overspeed and pressure head at inlet of unit. The results show that, the diameter of ACT can be 2 m smaller than the existing OST and it can decrease the fluctuation period from 130 s to 110.7 s while slightly increasing the overspeed in the last unit. The increasing delay time of the closing guide vane of last unit decreases the water fluctuation in ACT and OST and the maximum water fluctuation in OST and ACT reduce with slope −6.2% and −15% when ΔTd is in range of [14,25] seconds. Finally, the optimized dimension of ACT and OST provides essential guidance for decision-makers to deal with hydraulic transient in SULRP.