At a glance at elements
Hydroelectric power needs a huge construction site that contains many elements that fulfill the requirement of generation. Elements of hydroelectric power plants are Storage reservoir, Dam, Forebay, Spillways, Intake, Surge tank, Penstock, Draft tube, Tailrace, Turbine
The elements required for a hydroelectric power plant contain a Storage reservoir for water storage, a Dam to raise the head, and an intake structure for control and regulation purposes.
Penstock is a conduit system that carries the water from intake to the waterwheel. The Turbine is coupled with a generator to generate electricity. And a Draft tube.
Storage reservoir
Storage reservoir is used to store the water which is used as a fuel in hydroelectric power plant.
The main function of the storage reservoir is to store water during the excess flood (mostly in monsoon season) and supply it during the lean flow periods (long summers).
There are two types of storage reservoir natural reservoir and artificial reservoir.
Natural reservoir: Natural reservoir is generally lakes situated in high mountains or created by natural process.
Artificial reservoirs: artificial reservoirs are man-made dams constructed across the rivers.
The capacity of reservoirs depends on the head available for the power plant also the difference between run-offs during high and lean flows; generally, low head plants requires a large storage reservoir
Dam
There are two functions of a dam:
- To raise the water surface of the stream to create an artificial head
- The dam is also used as a water storage facility or pondage (small water storage behind river hydroelectric power plant).
Dams are the most expensive element of a power plant constructed with concrete or stone masonry and earth or rocky fill.
Choice of the dam is made according to the foundation conditions, the material used, transportation availability, and other hazards such as earthquakes.
The material used for construction dams is divided into two types: masonry dam and earth dam.
Masonry dam
Masonry dams are generally narrow cannels and can be classified into the following types
Solid gravity dam: construction material used for a solid gravity dam is concrete. The height of the dam is not generally very high and depends upon subsoil conditions.
Arch dam: these are curved shape dams where the narrow canyon width is available; however, it provides inherent ability against sliding.
Deck dam: the deck dams are constructed where the foundation is weak and an earthquake-prone site. It is generally inclined upstream to face water surges that create downward force and provides stability against over tuning or sliding.
Earth dam
Earth dams are constructed in the wide valley area and have a wide base; the height of the earth dam is comparatively high. It is comparatively less costly and can be erect easily. Mainly made from rock fills and sand.
Forebay
Forebay acts as a regulating reservoir for temporarily storing water during the light load period, just above the intake to store fluctuations. It acts like a pond behind a diversion dam which provides water during light load due to this wastage of excess water reduces. And plant functions effectively.
Forebays are generally in the form of an enlarged section of cannels.
Spillways
Spillways are the safety valve of the hydroelectric power plant.
The main function of spillways is to discharge water overflow to down the streamside when the reservoir is full.
It provides safety to the plant by discharging the overflow water so that excess water pressure does not hamper the dam.
It is generally made from concrete. Water discharges through opening shut off by metal control gates.
To maintain the water level in the reservoir, we need to control the degree to which gates are opened so that headwater discharge to the tailrace can be regulated.
Intake
Intake includes handworks structure at intake of conduits, tunnels/flumes. It is generally present before the turbine to prevent the intake of flumes and dust of water to the machines.
It prevents flumes, ice, and floating logs and diverts debris and ice into turbines. The intake structure consists of booms, screens/trash rocks sluices. The booms are used to prevent ice and floating logs by diverting them into bypass chutes. And the screen/trash to prevent the entrance of debris.
Surge tank
The surge tank is a small storage reservoir for receiving rejected flow and relive the conduit pipe (penstock) from excess water hammer pressure.
You might have thought we already have the reservoir, dam and Forebay then why do we need a surge tank?
A load of generators fluctuates from time to time. The reduction in load on the generator coupled to the turbine causes governs to close the turbine gates, which causes an increase in the pressure of penstock. This increase in pressure results in the water hammering phenomenon result could burst the penstock.
The same happens when the load on the generator increases. It causes the excess flow of water with high pressure on the penstock, creating a negative hammering phenomenon and damaging the penstock.
Suppose the water is stored in the surge tank. In that case, this surge tank is connected to penstock in negative and positive hammering conditions. Water flows through the surge tank. It causes smooth flow, which prevents hammering.
Penstock
Penstock is a close conduit that connects the Forebay or surge tank to the scroll case of the turbine.
In simple words, it is used as a pathway conductor for water from the water source to the turbine.
Draft tube
The draft tube is generally used for conveying water from the waterwheel to the tailrace. It connects a powerhouse (a building containing generators, turbines, accessories, and other miscellaneous) to the tailrace.
Tailrace
a race for discharging water that is wastage or already used for generation through the draft tube to away from the plant.
Turbine
And the last one is turbines. We will discuss what turbines are and the types of turbines in our next blog.
