EIA: Lao PDR - Asian Development Bank

EIA of The Nam Ngiep 1 Hydropower Project Draft Report: Chapter 2
valve section needs to be limited to within 10 m /s under any conditions in order to avoid
harmful vibrations. Considering these conditions, one (1) row of 0.8 m diameter discharge
pipe and two (2) sluice valves, each 1.1 m in diameter, are installed inside the dam body.
The upstream slide valve is for back-up. The sill level of the gate chamber is set at EL.
244.600 m, which is lower than MOL 296.0m and higher than the assumed sedimentation
level of EL. 233.0 m. The discharge is designed for a 5.5 m 3
/s discharge of riparian release.
2.4.8 MAIN POWER STATION
The layout of main power station and the spillway are designed so that they are closer to the
river center, considering that water from the spillway and the tailrace merge into the river.
The upstream end of the main power station elongated from the dam axis is 143.5 m long.
The main power station, a four-storey building, is approximately 25.0 m long, 62.5 m wide,
and 47.2 m high. The tailrace is 48.5 m long.
Two (2) Francis turbine units will be installed at the main power station, which will
generate energy for delivery to EGAT. (Table 2-2)
Table 2-2 Turbine Technical Data
Main Power Station
Type of turbines Francis turbine Vertical shaft
Number of turbines 2 (synchronous)
Nominal rotational speed 214 rpm
Nominal capacity at substation 272.0 MW (to be revised)
Generator terminal voltage 16.5 kV
Transformer Special three-phase Set-up to 230 kV
All generating units will be isolated and protected from the pressurized water supply by
inlet valves within the main power station. Draft tube gates of Francis turbine units will also
permit the isolation of a unit for inspection and maintenance, allowing the other units to
remain in service.
Power supply to the main power station, including the power generating equipment, will
be tapped from each of the Francis unit’s busbars through auxiliary transformers.
The power transformers will be arranged next to the power station building. The power
transformers of the main power station will be connected to the 230kV substation by means
of overhead lines.
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