Client: Lanco Teesta Hydro Power Limited
Project: Teesta Hydro-Electric Project Stage-VI- (4X125 MW)
Location: Teesta River, Sikkim
About Lanco Teesta Hydro Power Limited (LTHPL)
LTHPL is a Special Purpose Vehicle (SPV) taken over by NHPC. LTHPL envisaged developing 500 MW Teesta – VI Hydro Project over Teesta river in the state of Sikkim. The SPV is presently owned by NHPC, A Govt. of India Enterprise.
About the Project
Teesta Hydro-Electric Project Stage-VI- (4X125 MW) is a runoff river scheme over Teesta river, currently under development by LTHPL in collaboration with DMR.
The project envisaged the construction of a concrete barrage across River Teesta with upstream floor level at El. 342.5 m above mean sea level and the pond level (FRL) at EL. 360.0 m. Design discharge of 610 cumecs for the power generation was proposed to be tapped through 84.4 m wide power intake located at the right bank side of the river at u/s of the barrage. The water conductor system comprises 13.7 Km. long twin headrace tunnel (modified horseshoe type having a diameter of 9.8 m) on the right bank of river Teesta, each with a surge shaft. From each surge shaft, there were two pressure shafts/penstocks bifurcated to an underground powerhouse having an installation of 4 units of 125 MW each. The project affords annual design energy generation of 2441 GWh in 90% dependable flow in a year.
DMR was requested in 2015 to undertake the hydraulic re-design of the Barrage, Desilting system, and Surge shafts to make it compliant with the technical requirements of the Central Electricity Authority (CEA) and Central Water Commission (CWC).
The barrage was re-designed for passing the Standard Project Flood of 11600 cumecs considering CWC requirements of the enhanced waterway. The design of the desilting chambers was adjusted keeping in view the limited available space. The hydraulic design of the surge shafts conformed to the code requirements.
The re-designs of barrage and surface desilting chambers were required to be innovatively planned to ensure all technical requirements of CWC & CEA and were also required to be verified in the hydraulic model studies conducted in an independent reputed laboratory which was challenging. To consider operating the project at FRL (EL 360 m ) during the monsoon period for the effectiveness of the reservoir for silt trapping & effectiveness of desilting basins.
Value added by DMR
The re-design work of the project components by DMR has been substantiated as under:
- The design of the Barrage was made compliant with regulatory requirements by adding an additional bay of 15 m width for an additional discharging capacity of 2500 cumecs.
- The extra requirement of space for the barrage was met by modifying the dimensions of desilting chambers.
- The modified dimensions of desilting chambers were agreed to be based upon the requirement of 90% efficiency of 0.3 mm particle removal.
- The revised arrangement of desilting chambers was tested in the hydraulic model at IRI, Roorkee.
- The reservoir flushing studies for the barrage were also tested in the model by considering the reservoir at FRL during the monsoon.
- The surge tank needed modification with respect to orifice size, the bottom elevation of the pool, and the requirement of surge galleries to satisfy the stringent IS code conditions.
“The re-design of the project components by DMR led to successful approval of the designs which were stuck-up due to non-compliance of technical requirements and codal provisions. The core expertise and experience of the DMR team were evident from its willingness to go the extra mile for the project. The successful completion of the scope entrusted to DMR under various constraints proved the mettle of the team.”