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Sunday, January 3, 2016

Hydroelectric Power Plants

Introduction

Hydroelectric power plants convert energy available from flowing water into electricity. These power stations are suitable where water resources with sufficient head are available. When water is allowed to flow from the high elevation to a lower elevation, potential energy is transformed into kinetic energy, which is converted into electrical energy by the hydroelectric power plants.

The hydroelectric power plants can be divided into:
  1. Storage based power plants: these are the most common type and can produce electric power in huge quantities. A dam is built across the river bed creating a huge reservoir of water behind it.
  2. Run-off river or diversion power plants: A portion of a river or stream water is diverted to create a difference of elevation. These are small size plants and depend on availability of water for their operation.
  3. Pumped storage power plants: A pumped storage plant operates as a dual action water flow system. When the power demand in a power system is low, a part of energy generated by other power plants in the system is used to pump water from a lower level in front of a dam to a higher level behind the dam. In case of higher electric power demand the water behind the dam is used to produce electrical energy.The major functional parts are explained below. 
Dam or Reservoir

Stops the river's flow and forms a reservoir. The reservoir stores water during rainy seasons. It also helps to maintain a steady water head for the turbine to operate. The water level of the reservoir is called head race.

Tunnel

Tunnel is used to transport water from the reservoir to the generating station. It is normally made of RCC (Reinforced Cement Concrete).
Penstock


A penstock is a conduit that takes the water from the reservoir to the powerhouse. It is usually made of steel and is suitable for carrying water at medium to high pressure. For low-pressure penstocks, RCC pipes are also used.


(Photo courtesy http://sweetcrudereports.com)

Valve house


This is a facility to start or stop the water flow into the powerhouse for normal operation and for maintenance.
Surge tank

Surge tank is a small additional storage facility near the powerhouse. When the distance is more, non-uniform water intake to the powerhouse results in water hammering. The surge tank takes the sudden increase of pressure by allowing the water into it, when the water flow is stopped or reduced. Thus the surge tank functions as a pressure regulator in the water line.
Powerhouse

A powerhouse houses the turbine and the generator. The turbine converts the hydraulic energy from flowing water to mechanical energy. The generator, which is mechanically coupled to the turbine, converts mechanical energy to electrical energy. The used water from the turbine is released through the Tail race.

Factors to be considered:
  1. Quantity of water available
  2. Storage facility
  3. Head of water
  4. Accessibility
Advantages of hydroelectric power plants: 
  • No fuel is required for operating a hydroelectric power station. 
  • The generation cost is very low. 
  • Uses simple technology. 
  • Low start up time. 
  • It is a clean source of energy and no pollutants are generated. 
  • Generally hydro plants have longer life compared to other types. 
  • The dam and reservoir serve the purpose of irrigation and flood control also. 
Disadvantages of hydroelectric power plants:
  • It requires large area for installation. 
  • May affect the ecological balance of the area. 
  • High cost of construction. 
  • Long gestation period (time taken to get back returns after making the investment) 
  • The generation is weather dependent.
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