Thursday, October 18, 2007

Type of Turbines

Hydro power plants can be classified in various way,

1.According to Construction Features

An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level.

A diversion, sometimes called run-of-river, facility channels a portion of a river through a canal or penstock. It may not require the use of a dam.

Pumped Storage
When the demand for electricity is low, a pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

2.According to Size of Hydropower Plants

Facilities range in size from large power plants that supply many consumers with electricity to small and micro plants that individuals operate for their own energy needs or to sell power to utilities.

Large Hydropower
Although definitions vary, DOE defines large hydropower as facilities that have a capacity of more than 30 megawatts.

Small Hydropower
Although definitions vary, DOE defines small hydropower as facilities that have a capacity of 0.1 to 30 megawatts.

Micro Hydropower
A micro hydropower plant has a capacity of up to 100 kilowatts (0.1 megawatts).

For some good pictures of various types of hydro power plants visit EERE : Department of Wind and Hydropower Technology Programme website

3.According to Hydro power Turbines

There are two main types of hydro turbines: impulse and reaction. The type of hydropower turbine selected for a project is based on the height of standing water—referred to as "head"—and the flow, or volume of water, at the site. Other deciding factors include how deep the turbine must be set, efficiency, and cost.

All types of turbines are classified into 2 large divisions.

A.Reaction B.Impulse

A.Reaction :

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), or they must be fully submerged in the water flow.

Newton's Third Law i.e 'Every Action has Equal and Opposite Reaction' describes the transfer of energy for reaction turbines.Most water turbines in use are reaction turbines. They are used in low and medium head applications.

B.Impulse :

Impulse turbines change the velocity of a water jet. The jet impinges on the turbine's curved blades which reverse the flow. The resulting change in momentum impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy.

Prior to hitting the turbine blades, the water's pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades, and the turbine doesn't require a housing for operation.

Newton's second law describes the transfer of energy for impulse turbines.

Impulse turbines are most often used in very high head applications.

Examples :

Reaction turbines:

Impulse turbines:

4.According to Head or reservoir level

Ludins propose classification of hydro-plants based on head.

1.Low Head Plants : Less than 15 m head
2.Medium Head Plants : 15 m - 70 m
3.High Head Plants : 71 m - 250 m
4.Very High Head Plants : Above 250 m

Hydro power plants can also be classified based upon location,operation and turbine placement.

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