SUNKOSHI HYDROPOWER PLANT

1. Introduction

This is a report on field visit to Sunkoshi Hydropower station located at 81 km east from Kathmandu in Sindhupalchowk district. The powerhouse was commissioned in January 1972 with a friendly cooperation of the Water Conservancy and Electric Power Ministry of the People’s Republic of China and Government of Nepal. The cost of the project was approximately NRs. 109.37 million including transmission line up to Kathmandu. The cumulative generation of the station has reached 2,027.46 GWh in 2011/12 from the first run. The station has generated 60.36 GWh in FY 2010/11 and 66.38 GWh in FY 2011/12 with an increase of 9.99%. The station has a share of 1.59% of the total energy in the INPS in 2011/12.

2. Objective

ü  to know about the components of ROR hydropower project form intake to powerhouse

ü  to know how the components were laid and their working

ü  to know about the threats to hydropower project like landslide etc.

3. Salient features of Sunkoshi Hydropower Plant

The salient features of sunkoshi Hydropower station as obtained from the NEA website are :

Type	Run off River, Medium head plant
Location	Sindhupalchowk
Installed capacity	10.05MW
Annula design generation	70 GWh
River discharge	88 m3/s
Design discharge	39.9 m3/s
Maximum net head	30.5m
Length of canal	2.653 Km
Daily regulating pond capacity	67000 m3
Forebay capacity	18000 m3
Diameter of penstock	2.54m, 3 nos. with 13.3 m3/s discharge in each
Turbine Generator set	3 nos.
Shaft configuration	Vertical
Turbine	Type : Francis (Model HL123a-LJ-140) Output : 3530KW Speed : 300 rpm
Generator	Type : Synchronous, 3 phase (Model : TS 325/36-20) Capacity : 4000 KVA Rated voltage : 6.3 KV, 50Hz Rated current : 361 A Rated power factor : 0.85
Transmission Line	66KV, Single circuit
Project Inception date	End of 1968
Project placed in service	January 1972
Project financed by	People’s Republic of China and Government of Nepal
Project Cost	NRs. 109.37 million(including transmission line)

4. Components of Sunkoshi Hydropower Plant

The Components of Sunkoshi hydropower station visited are:

1. Dam

2. Intake

3. Headrace Canal

4. Settling basin

5. Spillway

6. Peaking pond

7. Forebay

8. Penstock

9. Power house

10. Tailrace canal

Each components are explained below :

            4.1 Dam

            The dam of sunkoshi consists of six radial gates as outlet gate with hoist for opening and             closing of gates when required. The dam increases the head, enough to divert the water                         towards intake. About 10% water are let pass towards the downstream of river for as an                       environment flow.

                        Radial gate : It is most common and economical type of gate. The radial gate is                                              operated by rotating around its hinge about horizontal axis. Opening and                                               closing of gate is controlled at the hoist above it. While opening it                                                         occupies less space than that of vertical gate.

                        Divide wall : The divide wall is provided to prevent cross current i.e. for one                                                directional flow.

                        Undersluice : Undersluice gates are provided to flush the sediments downstream                                               of river.

           

            4.2 Intake

               It is  a hydraulic structure constructed to withdraw required amount of discharge from river.           There are 4 side intakes in sunkoshi hydropower station. At entry, trash rack has been provided            to prevent entry of logs, floating bodies, dead   animals, etc.

                       

            4.3 Headrace Canal

            A canal is provided to convey the water from intake to forebay. A side canal has also        been provided which comes into use during cleaning of settling basin. The length of      canal is 2.653 Km.

           

            4.4 Settling basin

            The settling basin is one of the most efficient devices for hydropower schemes,    constructed on the head race canal for removal of sediment load upto 0.2mm diameter          particles from flowing water which cannot be trapped by gravity trap.

            The settling basin of sunkoshi consists of enlarged section at entrance to reduce the        velocity and hence the turbulence so that the bed load gets settled. Baffle walls are also          provided to facilitate the reduction of velocity. The settling basin is of hooper type. The        section of the basin becomes converging into similar shape and size of headrace         canal    at outlet.

           

            Flushing : When the sediments exceeds, deposited material tend to reduce X-                   sectional area of basin which increases the velocity ultimately decreasing the           trap     efficiency. So flushing should be done. In sunkoshi, three flushing gates are           provided with hoist for gate operation and flushing is continuous.

           

            4.5 Spillway

            To discharge the excess water, overflow spillway of ogee shaped has been provided at    downstream of settling basin.When water flows over the crest of spillway, it must         always remain in contact with or slide over the surface of spillway. The spilled water is          mixed with the river through the channel.

            4.6 Peaking Pond

            The peaking pond of the Sunkoshi Hydropower Plant is utilized during the dry (winter)     season when very low sediment concentration exists in the river. During the wet            (monsoon) season, the inlet gates of the peaking ponds are closed to stop the access of          sediment-loaded water. Since the peaking pond is located just upstream of the forebay             and is only used during the dry season, the annual sediment deposition rate in the peaking pond is low.

            4.7 Forebay

            A forebay or head pond is a temporary water storage, regulating reservoir provided at                downstream end of canal just at upstream of penstocks. At instance when turbine           rejects the load, it acts as a storage reservoir whereas it supplies water as a sort of     regulating reservoir when load increases.

           

            In sunkoshi, forebay has been provided just upstream of penstrock. A spillway has also    been provided at side of forebay to spill the excess water. The water spilled is mixed     into the river by dissipating its energy at stilling basin. Flushing gate has also been        provided to flush the sediments of forebay.

           

            Stoplogs has also been provided. It is a gate used to prevent the flow through spillway     or canal during the routine maintainence.

            4.8 Penstock

            Penstock is a pipe which carries water under pressure from forebays to turbine installed in powerhouse. Three penstock pipes has been provided in sunkoshi hydropower    station, each of diameter 2.5m and length 76m supported on saddle.

            4.9 Power house

            Power house is a multi-storeyed structure consisting of power generating equipments     like turbine, generator, switchboard, control room, etc. The net head is of 30.5m.

           

            In sunkoshi hydropower station, three turbine-generator units are provided. Water from            3 penstock pipe hit turbine. Control room is provided to manually control the power          generation. The type of turbine used is Francis turbine. It is reaction turbine and is used     for medium head hydropower project. In runner water enters radially and leaves axially    so it is also called “mixed flow turbine”. Major part of available water energy is    converted into kinetic energy at the entrance to runner and a considerable remaining        part is also utilized as pressure energy. Both kinetic and pressure energy are directly             converted into mechanical energy by turbine runner before generating electrical energy.

            Step up transformer is used to step the produced voltage of 6.3KV to 66KV.

           

            For control and protection device, there is 10 circuit breaker(3-generator,2-power           transfer,2-station supply and others 3 for local supply). MOCB(minimum oil circuit                beaker) has been replaced by VCB(Vacuum circuit breaker has been used). Natural air cooling, air forced cooling,water forced cooling are used as cooling system.

            4.10 Tailrace canal

            The function of tailrace canal is to discharge the water from powerhouse to river safely.