Khimti Power Plant
Khimti I Hydropower Plant is built with private sector funding as a “BOOT” agreement (Build, Own, Operate, and Transfer) with GON. Construction commenced on 26th June 1996 and Commercial Operation commenced on 11th July 2000.
HPL operates the plant and sells electricity to Nepal Electricity Authority (NEA). The plant will be transferred to GON at the end of the 50 year license period. At the end of the first Power Purchase Agreement NEA will purchase a 50% share in the Khimti Power Plant for a nominal fee.
The Khimti I Hydropower Project site is located in the Janakpur Zone, Central Development Region, some 100 km east of the Kathmandu. Khimti Khola forms the boundary between Ramechhap and Dolakha Districts. Access to the site is by the existing Jiri road 175 kilometres from Kathmandu.
The plant is a “run of the river” hydro-electric power generation plant designed for an installed generating capacity of 60,000 kilowatts and annual production of 350 million kilowatt-hours of electrical energy (350 GWh).
The site is located in Dolakha and Ramechhap District. The power plant utilizes a drop from 1270 to 586 meters above sea level in Khimti River, a tributary to the Tamakoshi River.
Construction work on the Khimti I Hydropower Project was started in early 1993 by the Butwal Power Company Limited and then gained momentum upon Financial Closure in June 1996. The major structures of the project include the Head-works (intake, de-silting basin), 7900m long headrace tunnel with 4 construction audits, 1000m long penstock tunnel, 900m access tunnel and 1470m long tailrace tunnel through a 6700m3 underground power house.
The civil design and construction works of the project were carried out under a contract by a consortium of NCC Tunnelling, formly Statkraft Anlegg (Norwegian company) and Himal Hydro (Nepali company). A consortium of Alston Power, formerly ABB Kraft and Kvarner Energy along with Nepal Hydro & Electric (Pvt) Limited carried out all electro-mechanical work. Similarly a consortium of Statkraft Engineering and BPC Hydro Consult had managed the project on behalf of HPL.
The project holds the record for achieving the highest national tunneling productivity; it has the longest headrace tunnel and penstock in the country. It is also the first project in Nepal to implement a Total Quality Assurance Scheme during construction. Above all, it is the first major hydropower project in Nepal to be completed within the original schedule despite very difficult tunneling conditions and other problems encountered.
The project utilizes a gross head of 684m in the Khimti River between the intake, at elevation 1270m, and the tailrace water in the Tamakoshi River at an elevation of 586m. Total length of the waterways including headrace and tailrace tunnel is in excess of 11km.
Hydraulic works consists of a low diversion dam, which leads the water through de-sanding chambers into the headrace tunnel. The tunnel is 7620m long with an 11.5 square meter cross section, and ends in a surge chamber, from where a 898m long, 45 degree inclined penstock shaft, with steel lining embedded in concrete, leads to the powerhouse. A 1418m long free flow tailrace tunnel with cross section of 15square meters brings the water into the Tamakoshi River. An 890m long tunnel with a cross section of 22 square meters provides access to the underground powerhouse at Kirne in the Tamakoshi Valley, just upstream of the confluence with the Khimti River.
The hydraulic works commence with the head-works (intake) consist of a low concrete/boulder sill structure in the steep river, diverting water to a two chambered settling basin. The basin is located in the open and clears of floods on the right river banks. It also includes a flushing system. De-sanding is particularly important in the “young himalayan mountains” with large amounts of loose material and heavy monsoon rain. This challenge has been solved in a relatively short geographical area through a flushing system called the S4. After the water leaves the flushing system it is lead into the headrace tunnel.
The tunnel is 7885m long with a nominal 11.5 m2 cross section and ends in a surge chamber from where a 1000m long 45 degree inclined penstock shaft with steel lining embedded in concrete leads to the powerhouse. A 1433m long free flow tailrace tunnel with a cross section of 15.5 m2 brings the water into the Tamakoshi River.
An 890m long tunnel with a cross section of 22 m2 provides access to the underground powerhouse at Kirne in the Tamakoshi Valley, just upstream of the confluence with the Khimti River.
The installation in the powerhouse consists of five double jet pelton turbines with runners fitted on the extended shaft of the 12,000 kilowatts, 750 RPM alternators. The power is transferred at 10.5 kilovolts from the generators through the cables in the access tunnel to the outdoor transformers where the voltage is stepped up to 132 kilovolts for supply to the national grid and to 33 kilovolts for local supply.
The outdoor switchyard is located near the powerhouse access tunnel portal at Kirne Besi. The total annual production is in excess of 350GWh.
|Catchment Area||358 km2||Average Precipation (Jiri)||2,212mm|
|Average flow at intake||31.5m3/s||Minimum daily discharge||3.5m3/s|
|Probable maximum flood (PMF)||3,900m3/s||Firm flow (90% exceedence)||4.11m3/s|
|Diversion weir crest elevation||1,272 m||Diversion capacity||11.65 m3/s|
|Diversion height||~ 2.5 m||De-sanding chambers||2 (two)|
|Chamber dimensions||90m x 12m x 2m|
|Headrace tunnel – Length||7,885 m|
|Steel lined penstock – Length||1,000 m (inclined)||Steel lined penstock Diameter||1.8-2.0 m|
|Tailrace tunnel – Length||1,433 m||Access tunnel – Length||890 m|
|Powerhouse, Turbine, Generators etc.|
|Number of Units||5||Number of units||5|
|Rated capacity||12.5 MW||Rated capacity||14.2 MVA|
|Running speed||750 rpm|
|Maximum static head||677 m||Transformers|
|Design head (net, full load)||660 m||Number of units||3|
|Rated flow at design head||2.15 m2/s||(2 x 28.4 MVA and 1 x 14.2 MV)|
|Power and energy output|
|Installed capacity||60 MW (net capacity after auxiliary use.)|
|Energy||350 GWh/yr (approx annual energy generation)|