Hydroelectric power plants convert potential and kinetic energy of water into electricity.
In hydroelectric production, potential energy of water is created by the construction of large dams. The dams hold the water at a greater height than the water level at the turbines.
Water is the greatest contributor of renewable energy to the world electricity generating system.
The common unit of measurement used to indicate the installed capacity of a hydroelectric power station is Megawatts.
Types of hydroelectric power plants
Based of design, hydro electric power plants are broadly divided into 2 types;
- Impoundment power plant
- Diversion power plant.
In the impoundment type of power plant, All water coming into the plant is dammed. The dammed water creates the head needed to power the hydro plant.
In the diversion type, the water coming to the plant is partially dammed, some water is allowed to flow back into the river immediately while the rest is used to power the hydro plant.
Head and tail water
In a hydro power plant system, the dammed water upstream is known as Head water and the water on the other side of the dam is known as Tail water. The difference between the top of the head water and that of the tail water is called pressure head.
Components of hydroelectric power plant
Trash rack; when water is coming fresh from the dam it needs to be cleared of big debris such as wood , plastic bags etc. the duty of the trash rack is to remove these.
Inlet gate; after water have been processed to remove debris, it then passed through the inlet gate. The inlet gate is used to regulate water flow into the turbines
Water conductors; water conductors are equipment used to convey water within the hydo electric power system. Example include; penstock, draft tube, scroll case, spill way, canals etc.
Penstock; the main pipe that conveys water to the turbine is known as penstock. It is a pressurized water conductor.
Spill way; a spillway is a water conductor used to prevent overflow of dammed water
Runner; the runner is part of the turbine system and it rotates as water from the penstock passes through it at high pressure
Power house; the power house houses the turbine, electric generators, transformers and other electric generating equipment
Open air switch yard; when the electrical transmission equipment is installed in open air, it is called an open air switch yard.
How a hydroelectric turbine works
Water with high pressure head on the upstream side of the dam is lead through large penstock pipe. Before the water get to the turbine it passes through a scroll case. The scroll case is a large curved pipe that helps the flowing water to efficiently rotate the turbine. The turbine is connected to the generator through a shaft. so as the turbine rotates, the connected generator also rotates producing electricity.
Advantages of hydroelectric power plant.
- It is a completely green process
- It is a very efficient way of generating electricity.
Disadvantages of hydroelectric power plant
1. It is always necessary for settlement around the dammed area relocate. This is because water required to run hydroelectric plants is extremely large and dammed water will cause flooding of the settlement.
2. It is capital intensive. This is because the hydro dams constructed are extremely large.
Types of hydro power plants
- Impoundment type power plant. This type of power plant utilizes a dam to impound large amount of flowing river water. The dammed water is the potential energy necessary to power the hydro plant. The different type of dams that could be used include; gravity, reinforced concrete, buttress, rock filled or earth dams.
- Diversion type power plant( run of the river). In this case, the river water is partially dammed, only part of the flowing water is utilized to produce electricity.
- Tidal water plant. This process works based on tidal action of water. it helps create a height difference on either side of the turbine, this pressure difference cause water to flow through the turbine rotating it.
- Pumped storage power plant. This type of plant basically consists of very large reservoir of water held at a very high level. The stored water is then made to flow downwards through a penstock pipe to run the turbine and generate electricity. After reservoir is depleted, the water is pumped back again and the whole process is repeated. Pumped storage power plant is a type of standby power generator.Its acts as a supplement and is usually made available to the national grid during peak hours
Types of turbines
Broadly of two types;
- Reaction turbine
- Impulse turbine
The reaction turbine are pressure turbines. When water flow through this turbine, it creates a pressure differential which causes the turbine to rotate.
Impulse turbine are pressure-less turbines. It rotates due to the kinetic energy given to it by a jet of water as its hits the blades.
Types of turbine runners
There are many types of turbine runners, however, the 3 most commonly used are;
- Kaplan runner
- Francis runner
- Pelton runner
Kaplan runners are types of turbine runners that can operate with medium to high water flows and efficient at low pressure heads. Kaplan runners are reaction runners because the pressure difference of the water flowing through the blades causes it to rotate.
Francis runners are reaction runners and can operate within a wider range of pressure heads than the Kaplan runners.
Pelton runners are only adequate for very high flows and operates within a narrower range compared to the Kaplan and Francis runners.