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1.1.Power Development under Srisailam Complex:-
The River Krishna is one of the major river systems in peninsular India and its basin has been and continues to be the cradle of civilization since ancient. Srisailam and Nagarjuna Sagar dams constructed one below the other on this river form two of the largest manmade lakes with combined gross storage of over 700 TMC ft. (20,000 million cubic meters). Such a system of two large reservoirs in cascade (one below the other) is unique. This affords development of Hydel Power in the conventional as well as pumped storage mode.
Srisailam dam forms the upper reservoir with a gross storage of 308 TMC ft (8700 million cubic meters). This dam has been constructed as a part of Srisailam Hydro Electric Project comprising the dam and a power station on the right bank with installation of 7 Nos., each of 110 MW Hydel units. This power station is presently in operation and contributes about 2300 million units of energy every year. Though originally conceived mainly as a hydroelectric project, irrigation projects have since been formulated and taken up for execution to draw water from Srisailam reservoir and feed parched lands in drought prone districts of Rayalaseema.
Nagarjuna Sagar Dam, which is about 100 KM downstream of the river from Srisailam forms the lower reservoir with a gross storage of 400 TMC ft. Taking advantage of the location of two large reservoirs one below the other, another project has been formulated and executed for development of peaking power by the principle of pumped storage operation. Srisailam Left bank Power Station is an underground power station with installation of 6 Nos., of each of 150 MW reversible type pump turbine motor generating units. This power station facilitates mopping up of surplus off peak thermal power in the system to supply it during peak hours. In addition it generates cheap conventional energy with monsoon surplus flows in the river. Stabilization of the grid and improving voltage are the additional advantages.
Brief details of the power Project are given in the following pages.
1.2.Working Process in Srisailam Right Bank Power House:-
The Main requirement for hydro-electric power plant is the availability of water in huge quantity at sufficient head and this requirement can be met by constructing a dam across a river. The schematic arrangement of a typical hydro-electric plant is shown in the following figure.
In Srisailam, an artificial storage reservoir is formed by constructing a dam across Krishna River. Near the bottom of the dam, there is a water intake. Trash Racks of 38meteis long are provided at the water intake to prevent the ingress of floating and other materials to the turbine. A Power tunnel of 720m long and diameter of 50 feet is taken off from the reservoir to the valve house at the start of Penstock. The valve house contains Bulk Head Gate for controlling water flow to the power station and automatic isolating valves for cutting off water supply in case the penstock bursts. A small storage reservoir called Surge tank (open at the top) is provided just before the valve house for better regulation of water pressure in the system to avoid the water hammer phenomenon.
From the reservoir the water is carried to valve house through power tunnel and from valve house to the water Turbine through pipes of large diameter 6.10m made of steel or reinforced concrete, called the Penstock. Gravity causes water to fall through the penstock inside the dam. At the end of the penstock there is a Francis reaction turbine which is turned by the moving water, converts Hydraulic Energy into Mechanical energy. The shaft from the turbine goes up into the 3-phase Alternator of capacity 122000KVA, which produces the power. The water after having done its useful work in the turbine is discharged to the tail race which may lead it to the river.
Each 11 kV phase of Alternator is fed to the primary of single phase 11/220 kV Step-Up transformer. The secondaries of the Transformers are connected to the 220 kV SWITCH YARD from where it is distributed as ten 220 kV feeders, two 132 kV feeders and five 11 kV feeders.
1.2.1. Main Control Room (MCR):-
The Control Room (or the operating room) is the NERVE CENTER of the power station. The various controls performed here are Voltage adjustment, load control, emergency tripping of turbines.etc. and the equipment and instruments housed in Control Room are Synchronizing equipment (Synchroscope), Voltage regulators, Ammeters, Voltmeters, Watt meters, Kwh meters, Kvarh meters, Temperature Gauges and other appliances, as well as Mimic diagram and suitable indicating equipment to show the opened and closed position of Circuit Breakers, Isolators..etc.,
1.3.Hydro Turbine:-
A hydro turbine converts the energy of flowing water into mechanical energy. A hydroelectric generator converts this mechanical energy into electricity.
The turbine is designed for direct coupling with three phase 50 Hz suspended type generator.