Hydroelectric Power Generation :
These convert energy of falling water (hydraulic) into Electrical energy. The entire arrangements can be divided into the following stages for the sake of simplicity :
1. Water reservoir.
2. Dam.
3. Valve house.
4. Penstock
5. Water turbine.
6. Alternator.
(Hydro Electric Power Station)
Hydro-electric plants may be classified according to the available head as:
(i) Hydroelectric Power Generation > Low head plants:
For such plants a small dam is constructed across the river to provide necessary head. The excess water is allowed to flow over the dam itself. No surge tank is required for such plants. In figure shows the arrangements of such a plant.
(Low Head Plant)
(ii) Hydroelectric Power Generation > Medium Head Plants:
The forebay provided at the beginning of penstock serves as water reservoir for such plants. In such plants water is generally carried in open channels from main reservoir to the forebay and then to the power house through the penstock. The forbay itself work as surge tank in this case. The common types of prime movers used in these plants are Francis, Propeller and Kaplan. General arrangement of such a plant is shown in the figure.
(Medium Head Plants)
(iii) Hydroelectric Power Generation > High Head Plants :
A typical arrangements for this type of plant is shown in the figure in such plants first of all water is carried from the main reservoir by a tunnel up to the surge tank and then from the surge tank to the power house in penstocks. For heads above 500 meters pelton wheels are used while for lower heads Francis turbine is used.
(High Head Plants)
Hydroelectric plants may also be classified as :
1. Hydroelectric Power Generation > Peak load plants :
A plant used only when the demand of power exceeds the limits of other power plants in the connected system.
2. Hydroelectric Power Generation > Base load plants :
Such plants have high load factors and continue to run for longer durations. Such plants must have enough availability of water. Peak load of such system may be shared by a diesel engine plant, gas turbine plant or even steam power plant
3. Hydroelectric Power Generation > Pumped storage plant :
Such plants are used when the quantity of water available for power generation is sufficient During peak period such plants generate power and the discharged water is collected in tail water pond. During off-peak hours, this water is pumped back to head water pond. Reversible turbines are used in these units so that the same unit can run as turbine for power generation and also as pump for pumping water.
Classification of Turbines:
(a) According to the action of water:
(i) Impulse turbines
(ii) Reaction turbines.
(b) According to the direction of flow:
(i) Radial outwards
(ii) Radial inwards
(iii) Axial flow
(iv) Mixed flow.
(c) Position of shaft:
(i) Horizontal
(ii) Vertical.
Following are the impulse turbines:
(i) Pelton wheel
(ii) Girard wheel
(iii) Jonal turbine
(iv) Banki turbine
(v) Turgo turbine.
Following are the reaction turbines:
(i) Fourneyron turbine
(ii) Francis turbine
(iii)Thomson turbine
(iv) Kaplan turbine
(v) Propeller turbine.
Performance of hydro turbine Turbines commonly used in hydro-power stations are Pelton wheel, Francis turbine and Kaplan turbine. The relative performance of these turbines is shown in the figure.
(Performance of Hydro Turbine)
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