What is hydroelectric power plant? A dam is set for the collection of water and water is accumulated in front of the flowing water in hydro power plants. Collected and settled water mass has a potential energy. Water mass with potential energy is sent to turbines with a certain speed from above.
Potential energy in settled water turns into kinetic energy when it starts to flow down. Kinetic energy turns into mechanical energy when the flowing water has entered the turbines. And water rotates the turbines and this mechanical energy is converted into electricity with energy generators.
Briefly Hydroelectric Energy:
Accumulated water at the dam has potential energy. Water flowing from above has kinetic energy. It has mechanical energy when the water rotates the turbines. It is in the form of electricity during the generation of electricity from the generator with the rotation of the turbines.
Potential Energy > Kinetic Energy > Mechanical Energy > Electric Energy
What Are Hydroelectric Power Plant Units? How Do They Work?
Hydroelectric power plants consist of 8 sections in total. These sections are Dam, Water Intake Section, Forced Pipes, Valves and Penstock, Filters, Turbines, Generators and Distribution Tables. Now let’s explain these sections in details.
1. Hydroelectric Power Plant Dam Section
One of the most important sections of hydroelectric power plants is the dam section. Parts which makes up the dam are as follows:
b) Filler and Penstock
d) Waste Outlet
e) Energy transmission sections
These are the parts that make up the dam section. Hydroelectric power plants are divided into 3 groups depending on their dam body and structure.
- Fill Dams (Rock Fill Dams)
- Concrete Dams (Made of Concrete)
- Mixed Type Dams (They have both filler and concrete body)
2. Water Intake Section
Water inputs are made to take the water to be used in the electricity generation phase to the suitable locations of the hydroelectric power plants. Water channels, pipes, force tunnels and cover are located in this section.
Water intake section is the adjustable section to supply sufficient amount of water at required speed for the electricity generation. Also, it is the section where materials, which can damage the forced pipes and turbines, such as stone, sand, and gravel in the water is kept.
3. Forced Pipes
Pressurized pipes between the turbine and the water channels are called forced pipes. The most important feature of the forced pipes used in hydroelectric power plants is the fact that they have a role to increase the pressure of water received water channels.
Forced pipes are produced from steel materials. And the parts that approach the water turbine of these pipes are smaller in diameter. This is due to increasing the water pressure.
Forced pipes make up the most of the cost of hydroelectric power plants.
4. Valves and Penstocks
Pipe safety valve is placed at the inlet and turbine valve is placed at the outlet of the forced pipes. If there may be any breakdown, tear or slip in the forced pipe, water entry will be prevented by closing the safety valve placed at the inlet of the pipe during the maintenance phase.
The types of valves used in hydroelectric power plants are as follows;
- Sliding Valve,
- Ball Valve,
- Conical Valve,
- The butterfly valve,
- Pressure Reducer Valve.
Forced pipe safety valves are butterfly type valves. Water is cut with sliding valve and conical valve when the turbine is stopped and it is necessary to supply for irrigation and other purposes. Pressure reducer valves are used to adjust the pressure in high-drop hydropower plants.
Filters prevent turbines from being damaged by keeping objects such as sand, gravel, stone, and wood in dam water by being placed to the intake ports of the hydroelectric power plants. The icing is prevented by supplying hot water to filters in order to prevent the filters from freezing in winter.
Turbines are the sections which convert the kinetic energy of water to mechanical energy. There are different turbine types according to the flow rate, fall, and pressure of the water. Turbine types used for hydroelectric power plants are as follows;
- Kaplan Turbines,
- Francis Turbines,
- Pelton Turbines.
These are the turbine types used in hydroelectric power plants.
a) Kaplan Turbines
Kaplan turbines are the most suitable turbines for low-drop and high flow rates. Their yields are quite high and this is because they have a very wide range of usage.
It is placed vertically together with alternator shafts. The winglet amount on the propeller is between 3 and 8. The winglets of these turbines are not fixed.
They are structurally similar to the Francis turbines. However, winglets are automatically adjusted with a servo motor connected to the rotor body that operates with oil pressure according to the varying load on Kaplan turbines.
If the load is fixed, fixed winglet Kaplan turbines are preferred.
The rotor diameter can be up to 10 meters in larger units. And turbine outlets can vary between 10 MW and 235 MW.
Operating principle of Kaplan turbines is ensured with the reaction force generated by the acceleration of the water at the rotor outlet but not with the thrust power of the water. In general, their structure is low and have two types of worm and non-worm.
b) Francis Turbines
Another turbine type used in hydroelectric power plants are Francis Turbines. These turbines are divided into three depending on their speed. These are fast, medium fast and slow. They are used in drops up to 300 meters and generally in medium-pressure hydroelectric power plants.
The operating principle of these turbines is the same as the working principle of Kaplan turbines. It operates with the pressure force with when the entrance and exit of the water to the rotor. Rotor wings in these turbines are fixed.
c) Pelton Turbines
Pelton turbines are impulse type turbines. These turbines are used at drops more than 300 meters. So they are used in hydro power plant with high-drop and low operating flow rate.
The yield of the Pelton turbines is very high.
Water is converted to water jet at the outlet by letting the water pass through suitable shape and diameter pipes in these turbines and kinetic energy is converted into mechanical energy in the turbine rotor by being sprayed onto the rotor blades in the form of a container. The generated energy varies depending on the sprayed energy amount.
The highest yield in Pelton turbines achieved when the rotor speed is half of the water jet speed.
Generators are machines that convert mechanical energy into electrical energy. Generators consist of two main parts as stator and rotor.
The rotor of the generators in hydro power plants is rotated by the movements of the turbine. The continuous flow that passes through excitation windings of the rotor creates a constant magnetic field. This magnetic field creates rotary magnetic field effect on stator with the rotation of the rotor. 3-phase voltage induction with a phase difference of 120 degrees between them occurs in rotating magnetic field windings on stator windings.
8. Distribution Tables
Auxiliary units are used in hydroelectric power plants for the continuity of the production and safety of the plant. Control rooms are built in the plants in order to check these units and all production is monitored and managed from these rooms.
Also, values such as current, voltage and hydro power generated by the hydroelectric power plant are constantly monitored.
Excitation systems, regulators, control and safety systems and communication systems are used in these control rooms.
Advantages of Hydroelectric Power Plants
Some of the advantages of hydroelectric power plants are as follows;
- No fuel costs,
- The number of employed workers is low,
- Energy unit cost is low,
- It does not suffer yield loss,
- Its structure is simple and robust,
- Maintenance costs are low,
- It adapts to load changes,
- The loss rates are very low,
- It does not pollute the environment.
The World’s Largest Hydroelectric Power Plants
1. Three Gorges Dam Hydroelectric Power Plant (China, 22.500 MW production capacity)
2. Itaipu Dam Hydroelectric Power Plant (Brazil-Paraguay, 14,000 MW production capacity)
3. Xiluodu Dam Hydroelectric Power Plant (China, 13,800 MW production capacity)
4. Guri Dam Hydroelectric Power Plant (Venezuela, 10.235 MW MW production capacity)
5. Tucuruí Dam Hydroelectric Power Plant (Brazil, 8,370 MW production capacity)