International Journal of Science, Engineering and TechnologyAuthors: Rajeev Prasad, Vinod Jhinkwan
Abstract: The first filling of a Water Conductor System (WCS) is the most critical non-operational test for any large-scale underground hydropower or pumped storage project. This process validates the structural integrity, water tightness, and geo-mechanical interaction of the system with the surrounding rock mass under hydrostatic pressure for the first time. This paper presents the philosophy and step-by-step methodology adopted during the first filling of the water conductor system at the 1000 MW Tehri Pumped Storage Plant. It also provides valuable insights and reference information for conducting first filling operations in similar large-scale hydroelectric projects. As a critical pre-commissioning activity, the first filling is designed to test the integrity and performance of all hydraulic components under controlled conditions for the first time. The methodology adheres to Indian Standard codes (IS 12633:1989) and project-specific requirements, implementing a phased, step-wise approach to pressurize the system gradually. The process is segmented into four distinct stages: Stage 1 involves filling the Tail Race Tunnel (TRT) up to the downstream surge shaft; Stage 2 covers the Head Race Tunnel (HRT) from the intake to the Butterfly Valve Chamber (BVC); Stage 3 entails filling the pressure shafts from the BVC to the Main Inlet Valve (MIV); and Stage 4 completes the balance filling of the upstream surge shaft. This paper provides detailed volumetric computations, filling discharge rates, prescribed waiting periods for strata stabilization, and a complete timeline for each stage. The total cumulative filling time, inclusive of all mandatory stabilization gaps, is calculated for two potential upper reservoir level scenarios (EL. 775 m and EL. 780 m), ensuring a controlled and safe commissioning process for the Tehri PSP.
