Koyna Hydroelectric Project
The Koyna Hydroelectric Project is the largest completed hydroelectric power plant of India. It is a complex project consisting of total four dams with the largest Dam built on Koyna River known as Koyna Dam hence the name Koyna Hydroelectric project. The project uses potential of water from Koyna River. The project site is situated in Satara district near Patan. The village Helwak near the dam was later known as Koynanagar.
The total Installed capacity of the project is 1,960 MW. The project consists of 4 stages of power generation. All the generators are located in the underground Powerhouses excavated deep inside the surrounding mountains of the Western Ghats. A dam foot powerhouse also contributes to the electricity generation. Due to the project's electricity generating potential the Koyna River is considered as the life line of Maharashtra.
The Koyna River’s hydro-electric potential undertook a general survey of hydro-electric possibilities in India in the first decade of the 20th century. After the first World War, a hydro-electric project on the Koyna river was investigated by the Tata Group. The 1928 financial crisis caused the project to be shelved. However after the independence of India, it was taken over by Government of Maharashtra. In 1951 Koyna dam division started to look into the project. The project got approved in 1953 and work commenced in early 1954.
The project is composed of four dams with major contributors Koyna Dam and Kolkewadi Dam. The water from Shivasagar reservoir formed by koyna dam is used for electricity generation in 1st, 2nd and 4th stages. This water is drawn from head race tunnels situated underground below the reservoir. Then it travels through vertical pressure shafts to the Underground Powerhouses. The discharged water from these stages is collected and stored in Kolkewadi Dam situated near village Alore at a lower level than Koyna dam. The water is drawn from penstocks of Kolkewadi dam to an underground power station in the 3rd stage and then discharged to the Arabian sea.
|Stage||Unit Number||Installed Capacity (MW)||Date of Commissioning||Status|
|Stage I||1||70||1962 May||Running |
|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 IV||16||250||1981||Running |
Besides this dam foot powerhouse part of power plant also produces 40 MW through 2 generating units of 20 MW each. Totaling 1960 MW in all. Details of each stage is given below.
Stage I and II
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 8 Pelton turbine units. Each of the two stages has 4 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 Navja into the head race tunnel. Then it travels towards the surge tank. It is further divided into 4 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 during this period which is used to generate electricity by the water which is discharged from the Koyna dam for irrigation purpose. It has 2 Francis turbine units of 20 MW capacity 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 a weir was proposed to divert the water coming out of Tail Race Tunnel of Stage I & II. But it was later observed that the water still had some hydraulic head of about 120 m which could be used. To use this head, a dam known as Kolkewadi Dam was constructed at this location. It serves the purpose of forming a balancing reservoir and maintaining the head. This dam impounds the tail race water from the first and second stages. This water is drawn through penstocks through the dam and electricity is generated by 4 Francis turbine units with a capacity of 80 MW each. The tail race water from these stages, which comes almost at sea level, is then flows through a cannel and joins the Arabian Sea near Chiplun.
The installed generating capacity of this stage is 320 MW.
Later in the 1980s, the electricity demand of the Maharashtra state increased tremendously which resulted in inadequate power supply in peak hours of demand. Considering need of power, the Planning Commission accorded approval to Stage IV with installation capacity of 4 × 250 MW. Thus, one more stage called Stage-IV was added to power system of Stage I and II, thus converting the Koyna Power Station into peaking power Station Complex with load factor of about 18.7%. This scheme also draws water from the existing Shivasagar reservoir same as 1st and 2nd stages.
A nonconventional intake system by piercing the lake from bottom by blasting the rock plug using dynamites is done for this stage. This double lake tapping process was done for this stage, the first of its kind in Asia, on 13 March 1999.
The water in head race tunnel is directly drawn from the reservoir and delivered to the head surge tank. Then four pressure shafts take the water vertically downward. The four huge Francis turbine units of capacity 250 MW each generate electricity and tail race water is taken into the Kolkewadi dam reservoir through tail race tunnel. A revolutionary Gas Insulated Switchgear system is used in the Underground 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 the electric grid.
Salient features of Koyna hydro-electric project
|Stage I & II||Stage III||Stage IV|
|Catchment area||891.78 km2 (344 sq mi)||25.04 km2 (10 sq mi)||Capacity of stage I & II is utilised|
|Capacity||2797.00 mm3||36 mm3|
|Max. height above foundation||103.02 m||63.30 m|
|Length||807.72 m||497.00 m|
|2. 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 Horse shoe shape|
|Discharge capacity||164 m3/s||170 m3/s||260 m3/s|
|3. Pressure Shafts|
|Length(each)||616 m||192 m||590 m|
|4. 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|
|5. Switch yard||4572 m||340 m||134 m × 18 m under ground|
|6. Load Factor||60%||24%||18% (1 + 2 & 4)|
• The water used for generation of electricity joins Arabian sea near Chiplun while the water which is discharges through the spillways of the dam in monsoon season joins the Bay of Bengal through Krishna River.
• All the components of the project such as Powerhouses, Head race and tail race tunnels, Pressure shafts are constructed underground.
• The modern Gas Insulated Switchgear system is used in 4th stage of the project
To utilise more water from the Shivasagar reservoir, another dam foot powerhouse is being constructed on the left bank of the dam. This Powerhouse will employ a pumped storage scheme. Also lake tapping is proposed for the intake system.
The impounded water of the Koyna Dam though has submerged a significant amount of Rain forest of the Western Ghats, it has helped a lot to the surrounding forest by supplying water all round the year. Hence a wide biodiversity of plants and animals is observed in the evergreen forest surrounding the reservoir area.
Koyna Wildlife Sanctuary
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 are Dhup (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 deers; pythons and cobras; common langurs and Indian Giant Squirrels. Many species of birds are found in the sanctuary including brown capped woodpecker; Asian Fairy Bluebird; and Crested Goshawk.
Another attraction of the sanctuary is Vasota Fort which lies deep in the forests and is located at a height of 1,120 m (3,675 ft) above sea level. The legend states that the fort was constructed by Malwa king Raja Bhoja in 1170.
Nehru Memorial park
When the project work was almost nearing completion, on 10 April 1960, the then Prime Minister of India Pdt. Jawaharlal Nehru visited Koyna Project. To commemorate this event a tablow was unveiled at his gracious hands on the right flank hillock of Koyna Dam. This project came up with an idea of immortalising 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 an auditorium named 'Yashogatha' (meaning: story of success) which reviles 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 the monsoon 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.
- Koyna Dam
- Koyna Wildlife Sanctuary
- List of power stations in India
- List of conventional hydroelectric power stations
- india-reports.com (india-reports.com) http://www.india-reports.com/articles/ElectricityInIndia/electricity_india_hydroelectric_largest_powerplant.aspx
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- "Under water lake tapping at Koyna project". Retrieved 29 December 2012.
- "Rane triggers lake tapping at Koyna". indianexpress.com (indianexpress.com). 1999-03-14.
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