Transient studies for downstream expansion chamber

In an underground power development, tailrace surge tanks are usually provided to protect tailrace tunnel from water hammer effect due to fluctuation in load. These are located immediately downstream of turbines discharging into long tailrace tunnels under pressure. The hydraulic design of downstream surge tank in Tehri HPP has been done so as to keep the surges within reasonable limits i.e., to accommodate the maximum and minimum anticipated water level under worst conditions of operation. Computer-aided surge analysis was carried out to design the surge tank (expansion chambers) provided in downstream of turbines. This paper describes the necessity of downstream expansion chamber and reasons for omission of surge tank in upstream of the water conductor system in Tehri HPP, and gives the main dimensions and design parameters for downstream expansion chamber, design methodology for extreme transient levels for downstream expansion chamber provided in Tehri HPP.