| Koyna Hydroelectric Project | |
|---|---|
 Koyna Dam | |
| Country |
|
| Location | Satara district, Maharashtra, India |
| Coordinates | 17°24′06″N73°45′05″E / 17.40167°N 73.75139°E /17.40167; 73.75139 |
| Status | Operational |
| Construction began | 1954 |
| Owners | Maharashtra State Water Resources Dept, Chief Engineer Electrical, Govt of Maharashtra |
| Operator | Maharashtra State Power Generation Company ltd |
| External links | |
| Website | www |
| Commons | Related media on Commons |
 | |
TheKoyna Hydroelectric Project is thelargesthydroelectric power plant inIndia.[1] It is a complex project with fourdams including the largest dam on theKoyna River,Maharashtra, hence the name Koyna Hydroelectric Project. The project site is inSatara district.
The Koyana Dam is situated near Koyananagar village. On river Koyana.
The total capacity of the project is1,960MW. The project consists of four stages of power generation. All thegenerators are located inunderground powerhouses excavated deep inside the mountains of theWestern Ghats. A dam footpowerhouse also contributes to theelectricity generation. Due to the project's electricity generating potential the Koyna River is considered as the life line of Maharashtra. The Sharavathi Pumped Storage Hydropower Project would be a larger project of 2000MWe in southern India and outside the Koyna plant.
The project takes advantage of the height of Western Ghats. Thus a very largehydraulic head is available over a very short distance.
In the early 20th century, there was a survey of the Koyna River as a potential hydro-electric source. After theFirst World War, a hydro-electric project on the Koyna river was investigated by theTata Group. The 1928 financial crisis caused the project to be shelved. In 1951 Koyna Dam division started to look into the project. The project was approved in 1953 and work commenced in early 1954. The second stage of the project was made using aWorld Bank loan (Project loan number 24-IN).[2]
The project is composed of four dams with the major contributors being theKoyna Dam andKolkewadi Dam. The water fromShivasagar reservoir was formed by the Koyna Dam and is used in the 1st, 2nd and 4th stages. This water is drawn from head race tunnels situated below the reservoir. Then it travels through vertical pressure shafts to theunderground powerhouses. The discharged water from these stages is collected and stored inKolkewadi Dam situated near village ofAlore. The water is drawn from thepenstocks of Kolkewadi Dam to an underground power station in the 3rd stage and then discharged to the Arabian Sea.
The electricity generated in all the stages is delivered to the mainelectrical grid. The project is run by theMaharashtra State Electricity Board.
| Stage | Unit number | Installed capacity (MW) | Date of commissioning | Status |
|---|---|---|---|---|
| Stage I | 1 | 70 | 1962 May | Running[3] |
| Stage I | 2 | 70 | 1962 August | Running |
| Stage I | 3 | 70 | 1963 January | Running |
| Stage I | 4 | 70 | 1963 February | Running |
| Stage II | 5 | 80 | 1967 June | Running |
| Stage II | 6 | 80 | 1966 November | Running |
| Stage II | 7 | 80 | 1966 June | Running |
| Stage II | 8 | 80 | 1966 March | Running |
| Stage III | 9 | 80 | 1975 July | Running |
| Stage III | 10 | 80 | 1976 January | Running |
| Stage III | 11 | 80 | 1977 May | Running |
| Stage III | 12 | 80 | 1977 | Running |
| Stage IV | 13 | 250 | 1981 | Running |
| Stage IV | 14 | 250 | 1981 | Running |
| Stage IV | 15 | 250 | 1981 | Running |
| Stage IV | 16 | 250 | 1981 | Running[4] |
Besides this dam foot powerhouse part of power plant also produces 40 MW through two generating units of 20 MW each, totalling 1960 MW. Details of each stage are given below.
The first stage of the project was approved in late 1953 and construction began in early 1954. Initially a two-stage construction was conceived. But the total generation capacity of the two stages was too large for load forecasts of that time. So a time lag of more than 10 years was proposed between the two stages. Within two years thereafter, it came to be noticed that the 10 years time tag between these two stages will not be affordable and to cope up with the power requirements, the two stages should be merged and both the stages should be constructed simultaneously. Hence, it was accepted that the two stages have to be executed as one.
The 1st and 2nd stages share same powerhouse with total eightPelton turbine units. Each of the two stages has four turbines having capacity of 65 MW each for 1st stage and 75 MW each for 2nd stage. The water from Shivasagar reservoir is taken through an intake structure known as Navja tower near village of Navja into the head race tunnel. Then it travels towards thesurge tank. It is further divided into four pressure shafts which run vertically downward delivering water to the turbines. Then the water is discharged into the tail race tunnel.
A dam foot powerhouse was also constructed which is used to generate electricity by the water which is discharged from the Koyna Dam forirrigation purpose. It has twoFrancis turbine units of 20 MW each. This powerhouse is run according to the irrigation requirements of the downstream areas.
The combined installed capacity of the two stages and the dam foot powerhouse is 600 MW.
Initially aweir was proposed to divert the water coming out of tail race tunnel of Stage I and II. But it was later observed that the water still had ahydraulic head of about 120 m which could be used. To use this head, theKolkewadi Dam was constructed at this location. It forms a balancing reservoir and maintains the head. This dam impounds the tail race water from Stage I and II. This water is drawn throughpenstocks and electricity is generated by fourFrancis turbine units with a capacity of 80 MW each. The tail race water from these stages then flows through a channel and joins theArabian Sea nearChiplun.
The installed generating capacity of this stage is 320 MW.
Later in the 1980s, the electricity demand of the Maharashtra increased tremendously resulting in inadequate power supply. The Planning Commission accorded approval to Stage IV with installation capacity of 4 × 250MW. Thus, one more stage called Stage IV was added to power system of Stages I and II, thus converting the Koyna Power Station into a peaking power station complex withload factor of about 18.7%. This scheme also draws water from the existingShivasagar reservoir same as Stages I and II.
A nonconventional intake system was created by piercing the lake from the bottom byblasting the rock plug usingdynamite.[5] This double lake tapping process was the first of its kind inAsia.[6]
The water in head race tunnel is directly drawn from the reservoir and delivered to the headsurge tank. Then four pressure shafts take the water downward vertically. The four hugeFrancis turbine units of 250 MW each generate electricity and tail race water is taken into theKolkewadi Dam reservoir through tail race tunnel. A revolutionary gas insulatedswitchgear system is used in theunderground powerhouse of this stage.
The installed capacity of this stage alone is 1000 MW. This stage is mostly used to cater for the peak hour demands of theelectric grid.
| Stage I & II | Stage III | Stage IV | |
|---|---|---|---|
| Dam | |||
| Catchment area | 891.78 km2 (344 sq mi) | 25.04 km2 (10 sq mi) | Capacity of stage I & II is utilised |
| Capacity | 2797 MCM | 36 MCM | |
| Max. height above foundation | 103.02 m | 63.30 m | |
| Length | 807.72 m | 497.00 m | |
| Intake works | |||
| Head race tunnel length | 3748 m | 4551 m | 4230 m |
| Intake tunnel diameter | 6.4 m circular | 7.4 m D shape | 7 m × 9.50 m horseshoe shape |
| Discharge capacity | 164 m3/s | 170 m3/s | 260 m3/s |
| Pressure shafts | |||
| Number | 4 | 4 | 4 |
| Length(each) | 616 m | 192 m | 590 m |
| Power house | |||
| Approach tunnel length | 864 m | 780 m | 988 m |
| Tail race tunnel length | 2215 m | 4543 m | 2314 m |
| Number of turbines | 4 (stage I) + 4 (stage II) + 2 (dam foot powerhouse) = 10 | 4 | 4 |
| Type of turbine | Pelton (stage I & II) Francis (dam foot powerhouse) | Francis | Francis |
| Installed generation capacity | 600 MW | 320 MW | 1000 MW |
| Switch yard | 4572 m | 340 m | 134 m × 18 m underground |
| Load factor | 60% | 24% | 18% (1 + 2 & 4) |
To utilise more water from theShivasagar reservoir, another dam foot powerhouse is being constructed on theleft bank of the dam. Thispowerhouse will employ apumped storage scheme. Also lake tapping is proposed for the intake system.
The impounded water of theKoyna Dam though has submerged a significant amount ofrain forest of theWestern Ghats, it has helped a lot to the surrounding forest by supplying water all round the year. Hence a widebiodiversity of plants and animals is observed in the evergreen forest surrounding the reservoir area.
Koyna Wildlife Sanctuary has dense forests with three major sections, Vasota, Maharkhor and Indavli Met, and the sanctuary is endowed with natural protective boundaries –Shivasagar Lake on one side, and the slopes of the Western Ghats on both the sides. This protective cover has enabled the emergence of a diverse variety of flora and fauna in the sanctuary. Some of the endangered species of trees found in the sanctuary areDhup (Boswellia serrata),Euphorbia longan, andElaeocarpus spp., apart from many other species of trees. The sanctuary has a diverse variety of fauna including tigers and panthers; gaurs and sambars; barking and mouse deer; pythons and cobras; commonlangurs andIndian giant squirrels. Many species of birds are found in the sanctuary including brown capped woodpecker;Asian fairy bluebird; andcrested goshawk.
Another attraction of the sanctuary isVasota Fort which lies deep in the forest and is located at a height of 1,120 m (3,675 ft) above sea level. The legend states that the fort was constructed byMalwa kingRaja Bhoja in 1170.
When the project work was nearing completion, on 10 April 1960, the thenPrime Minister of India Pt.Jawaharlal Nehru visited the Koyna Project. To commemorate this event a tableau was unveiled at his gracious hands on the right flank hillock of Koyna Dam.This project came up with an idea of immortalizing this place and this event by constructing a beautiful park and naming it as "Nehru Memorial Park". This park is a major attraction for tourists. An upstream side view of dam is visible from this garden. There is anauditorium named 'Yashogatha' (meaning: story of success) which relives a small element of the tremendous efforts taken by the engineers and workers associated with project.
Due to the large rainfall in the hilly region surrounding the reservoir, some beautiful falls are generated in themonsoon season. The largest of them is the Ozarda falls near Navaja village 10 km from Koyna. This is also a major attraction for tourists visiting in monsoon season.
