Hydraulic Turbine Definition:
Hydraulic Turbine is a device that converts the energy in a stream of fluid into mechanical energy by passing the extreme through a system of fixed and moving blades and causing the wheel to rotate.
In simple terms, the Turbine is like Power producing machines.
Water turbine was developed in the 19th Century and widely used for industrial power prior to electrical grids. This is mostly used for electric power generation. They harness clean and renewable energy sources.
Flowing water is directed on the Blades of a turbine runner, creating a force on the blades.
Since the runner is spinning, the force acts through a distance. In this way, the energy is transferred from the water flow to the turbine.
Hydraulic Turbine Classification:
1. According to the type of energy at Inlet:
- Impulse Turbine: The energy is in the form of kinetic. e.g: Pelton wheel, Turbo wheel.
- Reaction Turbine: The energy is in the form of both Kinetic and Pressure. e.g: Tubular, Bulb, Propeller, Francis turbine.
2. According to the direction of flow through Runner:
- Tangential flow: water flows in a direction tangential to the path of rotational, i.e. Perpendicular to both axial and radial directions.
- Radial outward flow e.g: Forneyron turbine.
- Axial flow: Water flows parallel to the axis of the turbine. e.g: Girard, Jonval, Kaplan turbine.
- Mixed flow: Water enters radially at the outer periphery and leaves axially. e.g: Modern Francis turbine.
3. According to the head under which the turbine works:
- High head, (Impulse turbine. e.g: Pelton turbine.)
- Medium head, (Reaction turbine. e.g: Francis turbine.)
- Low head, (Reaction turbine. e.g: Kaplan turbine, propeller turbine.)
4. According to the specific speed of the turbine:
- Low specific speed, (Impulse turbine. e.g: Pelton wheel.)
- Medium-specific speed, (Reaction turbine. e.g: Francis wheel.)
- High specific speed, (Reaction turbine. e.g: Kaplan and Propeller turbine.)
Let’s know the Impulse turbine in details:
The impulse turbine changes the velocity of the water jet.
The jet impinges on the turbine curved blade which changes the direction of the flow. The resulting change in momentum (impulse) causes a force on the turbine blades.
Since the turbine is spinning, the force act through a distance (work) and the diverted water flow is left with diminished energy.
Prior to hitting the turbine blades, the water pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine.
No pressure changes occur at the turbine blades, and the turbine doesn’t require housing for operation.
- Newton’s second law describes the transfer of energy for impulse turbine.
- Impulse turbines are most often used in a very high head application.
- This turbine works at atmospheric pressure.
- The Impulse turbines are- Turgo, Jornal, Banki, Girad and Pelton Turbine.
Reaction turbines are acted on by water which changes pressure as it moves through the turbine and gives up its energy. They must be encased to contain the water pressure (or suction), there must be fully submerged in the water flow.
- Newton’s third law describes the transfer of energy for the reaction turbine.
- Most water turbines used a reaction turbine.
- They are used in low and medium head application
- This turbine works above the atmospheric pressure.
- The Reaction turbines are- Thompson, Francis, Kaplan, Fourneyron and Propeller Turbine.
Hydraulic Turbine Working Principle:
So, the working principle of this turbine is, according to Newton’s law, A force is directly proportional to the change in momentum. If there is any change in momentum of fluid then a force is generated.
The hydraulic turbine blades (in case of Pelton wheel) are provided against the flow of water which changes the momentum of it.
As the momentum is changing, a resulting pressure force generated which rotates the rotor or turbine.
As the change in momentum high, the force generated is high, which increases energy conversion.
So the blade or buckets are designed so that it can change the maximum momentum of the water.
This turbine is used in a hydroelectric power plant.
Hydro-Electric Power Plant:
In 2012, hydroelectric power plants contributed about 16% of the total electricity generation in the world.
Hydroelectricity is the most widely used form of renewable energy. It is a flexible source of electricity and also the cost of electricity generation is relatively low.
It consists of the main 6 parts:
Dam and Reservoir:
The dam is constructed on a large river in hilly areas to ensure sufficient water storage at height. The dam forms a large reservoir behind it.
The height of the water level (called a water head) in the reservoir determines how much potential energy is stored in it.
Water from the reservoir is allowed to flow through the penstock to the turbine.
The amount of water that is to be released in the penstock can be controlled by a control gate. When the control gate is fully opened, the maximum amount of water is released through the penstock.
The potential energy of the water is converted into kinetic energy as it flows down through the penstock due to gravity.
Water from the penstock is taken into the water turbine. The turbine is mechanically coupled to an electric generator. The kinetic energy of the water drives the turbine and consequently, the generator gets driven.
A generator is mounted in the powerhouse and it is mechanically coupled to the turbine shaft.
When the turbine blades are rotated, it drives the generator and electricity are generated which is then stepped up with the help of a transformer for the transmission purpose.
Surge tanks are usually provided in high or medium head power plants when a considerably long penstock is required.
A surge tank is a small reservoir or tank which is open at the top. It is fitted between the reservoir and the powerhouse. The water level in the surge tank rises or falls to reduce the pressure swings in the penstock.
Difference between Impulse and Reaction turbine:
|SL NO||IMPULSE TURBINE||REACTION TURBINE|
|1||All hydraulic energy is converted into kinetic energy by a nozzle.||Only some amount of the available energy is converted into kinetic energy.|
|2||It requires very little maintenance.||Here it’s required more maintenance.|
|3||The degree of reaction is zero.||The degree of reaction is between ‘0’ & ‘1’|
|4||It needs a low discharge of water.||It needs medium and high discharge of water.|
|5||Water flow is a tangential direction to the turbine wheel.||Water flow is a radial and axial direction to the turbine wheel.|
|6||Here is having more hydraulic efficiency.||It’s having relatively less efficiency.|
|7||Impulse turbine operates at high water heads.||It operates at medium and low heads.|
|8.||An example of an impulse turbine is the Pelton wheel.||An example of a reaction turbine is Francis, Kaplan turbine.|
|9||Flow regulation is done by means of a needle valve fitted into the nozzle.||Flow regulation is carried out by means of guide vane assembly.|
|10||The turbine is always installed above the tailrace and there is no draft tube used.||In the reaction turbine, the turbine is generally connected to the tailrace through a draft tube which is gradually expanding passage.|
|11||The turbine doesn’t run full and air has free access to the bucket.||Water completely fills at the passage between the blades and while flowing between the inlet and outlet sections does work on the blades.|
|12||Water is admitted only in the forms of jets. There may be one or more jets striking an equal number of buckets simultaneously.||Water is admitted over the entire circumference of the runner.|
Hydraulic Turbine Advantages:
- This is a renewable energy source. The water-energy can be used again and again.
- This turbine having high efficiency.
- The running cost of the Hydraulic turbine is less as compared to other turbines.
- Since Dams are used. So it is used for power generation.
- The environmental pollution system is negligible here.
- This is easy to maintain.
- The main advantages of the Hydraulic turbine are that at the turbine place, the people can visit and come across all the main parts in detail. This is like an open system.
Hydraulic Turbine Disadvantages:
- The Installation or Initial cost is very high. This system or plant takes several decades to produces the profit.
- It can develop at only a few sites where the proper amount of water is available.
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