Koyna Hydro-Electric – a Marvel of Engineering
Let the clichï¿½s of wonderment be summoned to describe it. A look-ever would be simply breathtaking. However it may be called, it is undoubtedly an amazing engineering feat – it is the Koyna Hydro-Electric Power Project, called the K.H.E.P. Carved in the majestic Sahyadri Hills of Western Maharashtra, the K.H.E.P. puts to full use the gift of nature – high hills resulting in considerable water-head and the steep tapers of the range towards the Arabian Sea – resulting in generation of hydro-electricity that forms the life of the Western grid. Its output has made Maharashtra self -sufficient; providing power to run industrialised demands and agricultural systems across vast stretches of the state.
A drive across the Koyna region, a scenic marvel, reveals a beautiful liaison between modern technology and nature. Caverns and tunnels, dug deep into the rugged hills, form the framework of this project – all replete with the most modern gadgets and protection systems. The project comprises of four stages – spread out in a region encompassing land in the Satara and Ratnagiri districts.
KOYNA 1ST & 2ND STAGES:
The first stage was developed at Pophali near Koyananagar. Work had commenced on the 16th of January 1954. Two years later began the staggering work of excavation of approach and ventilation tunnels. Stage 1 of the project has four generators of 70 MW and the 2nd stage of the project has four generators of 80 MW, both of which have been recently uprated.
The first two stages involved several developmental levels – including the construction of a concrete dam at Koyna, excavation of head-race and tail-race tunnels, filling of the Shivaji Sagar Lake, among other things. Construction is deep underground – an elucidation of the great civil engineering prowess that has gone into this massive undertaking. Penstocks, fortified with concrete and steel, run through the mountains to give the source for generation. There are four sets of transformers (each set having 3 transformers) each for the 1st and 2nd stages having capacity of 25 MVA for the 1st stage and 30MVA for 2nd stage with a step-up capacity of 11/138.6 KV. A spare is provided for each stage.
Cranes are situated underground, while machine halls, EVT, valve house, workshop and GIS (Gas Insulated Switchgear) are arranged intricately in the huge underground complex. The whole construction, well-ventilated and air-conditioned, is divided into three floors. Each floor has different equipment. On the lower-most floor are located the AEG-Germany-manufactured generators. All the maintenance and protection gadgets for the alternators are also present. Transformers, Italian-make in stage I and Japanese in stage II are mounted on the same floor.
The 2nd floor has the shaft section where the breaking system can be observed. Automatic controls and computerised monitoring are present on all sections. Several parameters like speed of turbine rotation, temperature of windings, output power levels and other things can be seen by the click of a mouse. There are auxiliary generators for excitation purpose and a DC power system to operate electronic equipment related to control and relay.
From the switch-yard exit two 220 KV double circuit transmission lines to Pedhambe near Chiplun and to Kandalgaon and New Koyna with one line leading to Karad.
The Shivaji-Sagar lade is the reservoir for this stage. The catchment area is about 892 square kilometres.
KOYNA STAGE 3:
This is located in Alore in Chilpun Taluka. This has a smaller catchment area of about 25 square kilometres.
The generators are manufactured by Bharat Heavy Electricals Limited (BHEL). The 3rd stage includes an emergency observation tunnel, amid remote highlands of the Sahyadri range.
4 vertical shaft Francis turbines coupled to 4 80 MW alternators form the power generating system.
KOYNA STAGE 4:
Stage 4 is a recent development of the Koyna Hydel Project. It is located at Kolkewadi. Construction began in 1985 and completed in about April 2000. The stage 4 is bewildering maze of caverns, situated several kilometres deep into the hills. A visit to this site is followed by traversing a nine-kilometre long well-lit approach tunnel. At the end of this tunnel towards the entrance of the powerhouse, the air is stale and nauseating. But the moment one enters the main gate, the atmosphere changes, thanks to a well-ventilated ambience served by air-conditioning systems running in pipes through a ‘ventilation tunnel’.
The interiors are exciting to observe – with equipment and machine systems galore – many of them unmatched all over Asia. This is what has made the powerhouse so efficient and economical, resulting in cheap electricity – a hallmark of this project.
The total construction area is about 144m(L) ï¿½ 45m(H). The whole construction has five distinct floors. The stage has a head of 510m. The water is directly taken from the Shivaji Sagar reservoir. Penstocks lead from the Koyna Dam. Lake tapping technology, which has been used for the first time in India, has made this possible. Francis turbine is used due to availability of sufficiently high head. This means 250 MW from each of the four French GEC – Alstom – Electromechanique – Belfort – manufactured alternators. The plant is also able to generate 310 MW for at least 1.5 hour for peak loads whenever necessary.
The five floors exhibit a vast array of modern equipment. The lowermost floor has the main control room which is fully computerised – that includes touch-screen panels and world-class power systems software. Every activity in the powerhouse is monitored. Winding temperature, water discharge, speed of alternator etc. can be observed with remarkable ease. Graphical views can be obtained without any hassle. Records are maintained up-to-date. There are two local control rooms which can also control several operations – these being under the command of the main control room.
Fire-fighting equipment is very sophisticated. Water-sprinkling system avoids overheating of the alternator. It produces 11 KV output to transformer. The output from the alternator is carried by octagonal conductors to the transformer. These conductors have the capacity to carry 13,200 A to the transformer. 100 MVA oil-cooled transformer with step-up capacity of 16/400 KV are used. They are manufactured by BHEL, Bhopal.
The plant has a unique underground switchyard using 400 KV XLPE cables, about 105m in length. SF6 circuit breakers, engineered to work underground for only the second time in India, are used in conjunction with the Japanese-manufactured cables.
Control cables are specially designed and fitted in a rectangular shaped hollow box. The aluminium conductor is of thickness 3-4 mm. It is insulated by asbestos-like material which is able to with stand very high voltages.
The penstock is about 590m long. Spherical and butterfly values control the flow of water to the runner. Two servomotors operate the valves – they are ? oil-operated and ?rd air-operated. The 131m high surge tank is completely dug in the mountain and connected to the penstock. The draft tube and discharge tunnels are so constructed that the runner can be closed down for maintenance without hindering the performance of the alternator.
Very remarkable about the stage 4 is the step-down substation. Built on French technology, it is unique in Asia. Most sophisticated equipment including isolators, SF6 circuit breakers and ultra-modern transformer bays make up this sub-station. This leads into a cable tunnel that forms yet another part of this astonishing labyrinth.
Consistent and reliable, efficient and economical, ultra-modern and environment-friendly – Koyna Hydro-Electric has rendered yeoman’s service to the nation by delivering power besides boosting up agricultural production by its provision for irrigational development. One of the biggest hydro-electric generation projects in India, Koyna is definitely one of the greatest technological achievements of our independent nation – beyond doubt, a marvel of engineering.