Feasibility Study, Detailed Engineering Design, Tender Documentation, and EIA of Sardi Khola Hydroelectric Project and Transmission Line including Access Road

Project Description

Sardi Khola is a small tributary of Seti River with a total Catchment area at intake of 27 km2, maximum elevation within catchment 4070m, has occasional snow cover. The Project was designed as a run of the river project with steel pipe as the main water conveyance system. The design hydrological parameters were:
• Design discharge = Discharge with 40% exceedance probability (Q40) = 2.14 m3/s
• Design flood(Flood,Q100) = 131 m3/s at intake, 160 m3/s at Powerhouse
• Dominant mineral distribution in the suspended sediment is Mica (>40%) with presence of Quartz <20% Available Design Head : The gross design head available is 250.3m and the net design head is 230.3m after the total maximum head loss of 20.0m, which is 8.0%. Headworks: Weir: Total 26m long, 2.5m high divided into two sections: i) 20m overflow section and ii) 6m under-sluice section with 2 bays of 2.5m each with a 1.0m pier in between Intake: Two rectangular orifice of size 1.50m width x 1.0m height Gravel Trap: 3.0m wide x 1.0m deep Approach canal: 2.0m wide x 1.5m deep Settling Basin: Length 20m plus transition (4m at inlet and 3m at outlet), 2 bays of 2m width and 3m depth, designed for 90% removal of particles equal and larger than 0.2mm size. Forebay: Length 30m x width 4m x depth 3m, designed to retain inflow volume for 3 minutes. Water Conveyance System As a result of study of possible alternatives, the optimal water conveyance system for the project resulted in a steel pipe of diameter 1.0m. The total length of the pipe from settling basin to the turbine is 2975m which is divided into two nearly equal sections of low pressure headrace pipe and high pressure penstock by introducing a fore-bay at mid-length. Powerhouse A surface powerhouse is designed at the right bank of the river at ward no. 6 of Sardi VDC. The area is the extension of flood plain privately owned and cultivated. Land acquision is required for this area only. Electro-mechanical Design Turbine: Two units of double jet horizontal axis Pelton turbines with axis at elevation 1298.00m. Nameplate capacity of each unit is 2 MW. Generator: The generator selected is a 3-phase horizontal shaft, ordinary type synchronous generator with a salient pole revolving field and AC brushless exciter. The cooling system shall be of the self-ventilating and recalculating type with water-cooled air coolers. The continuous rating of generators shall be 2400 kVA under following conditions: Rated Voltage 6.6 kV Rated current Frequency 50 HZ Rated power factor 0.85 lagging The rated speed of the Generator shall be 600 rpm. The generator shall be designed to withstand the maximum runaway speed of 1200 rpm for a period of 15 minutes. Direction of rotation shall be clockwise as viewed from end. Transformer Two nos of 2.7 MVA 6.6 kV three phase step up power transformers will be installed in the switchyard. Each of two generators will be directly connected to 2.7 MVA 6.6/33 kV three phase transformers. Each set of the two power transformers will be connected to 33 kV single bus bar systems through their individual 33 kV isolators and gas circuit breakers. Average annual energy generation is 22.106 GWh, out of which 3.553 GWh is dry season energy. Total Project Cost NRs. 650.114 million

Assignment Description

The services provided included the following: • Feasibility study and Environment Impact Assessment (EIA) of Transmission line • Survey and Investigation : This included detailed topographical survey, hydrological survey, geological survey • Review of past study document • Capacity optimization • Social & environmental study with action plan • Detailed Design of the Project • Civil Design • Electromechanical Design • Hydro-mechanical Design • Tender and Contract Document Preparation Civil design consisted in hydraulic and structural design of facilities for diversion of water, exclusion of sediment and conveyance of water from intake to the turbine and the design of powerhouse to accommodate the electro-mechanical equipment for power production. The design philosophy has remained to design these structures as small and light as is just required to serve the purpose and keep functional all the time with minimum closure. Electromechanical design consisted in selection of the type of turbine and number of units and determining the specification for the current generator, transformer and all appurtenant equipment.