Energy

Nam Theun I HPP

Nam Theun I HPP

Laos

The 650 MW Nam Theun 1 HPP is located at Nam Kading River, approx. 33 km upstream of its confluence with the Mekong River and 270 km from Vientiane in Central Laos (Boli khamxai province).

The main structure of this project is the 177 m high curved gravity RCC dam that supports a centrally located 6 bays gated crest spillway with a conventional concrete chute and flip bucket capable to spill a flood of 23,500 m3/s, located in a narrow gorge with reasonable geological conditions.

The powerhouse is located on an excavated platform on the left bank of the river, about 450 downstream of the dam with 3 turbine generator Francis units (2x260 MW for EGAT and 1x130 MW for EDL) located in two deep circular shafts and a pressure  (tunnel/shaft)  power waterway common to all three units to be driven through the left abutment of the dam  from a large self-starting outdoor power intake located upstream of the dam.

The inherent advantage of this solution is because the powerhouse is separate from the dam site, it allows works to progress on various locations at the same time with far less disruption of construction works during the high water periods.

The diversion tunnel located on the right bank is designed to only pass the design floods of the Nam Kading River during the dry season while allowance is made for overtopping of the two cofferdams and the dam construction site during the high floods of the rainy season.