Hydro-Electric Power Plant

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Hydro-Electric Power Plant
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• Introduction
• One of the most widely used renewable source of
  energy for generating electricity on large scale
  basis is hydropower
• The power obtained from river or ocean water is
  called as hydropower.
• Hydropower is the renewable source of energy
  since water is available in large quantities from
  rain, rivers, and oceans and this is will be
  available for unlimited time to come.
• 30 of total power of the world is met by
  hydro-electric power.
• Total hydro-potential of the world id 5000 GW.

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Essential features of Hydro-Electric Power Plant

• The essential features of a water power plant are
  as below
• 1. Catchment area.
• 2. Reservoir.
• 3. Dam and intake house.
• 4. water way.
• 5. Power house.
• 6. Tail race or outlet water way.

• Catchment Area.
• The catchment area of a hydro plant is the whole
  area behind the dam, draining into a stream or
  river across which the dam has been built at a
  suitable place.

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• 2- Water reservoir
• In a reservoir the water collected from the
  catchment area is stored behind a dam.
• Catchment area gets its water from rain and
  streams.
• The level of water surface in the reservoir is
  called Head water level.
• Note Continuous availability of water is a
  basic necessity for a hydro-electric power plant.
  
• 3- Dam
• The purpose of the dam is to store the water and
  to regulate the out going flow of water.
• The dam helps to store all the incoming water. It
  also helps to increase the head of the water. In
  order to generate a required quantity of power it
  is necessary that a sufficient head is available.
  

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• Dam are classified based on following factors
• Function
• Shape
• Construction material
• Design
• a) Based on function the dam may be called as
  storage dam, diversion dam or detention dam.
• Based on the shape the dam may of trapezoidal
  section arch type.
• c) The materials used for constructing
  dams are earth, rock pieces, stone masonry.
• According to structural design the dam maybe
  classified as
• Gravity dam
• Arch dam
• Buttress dam

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Types of Dam

• Masonry Dams.
• Earth Dams.
• The masonry dams are of three major classes
• Gravity dam.
• Buttress dam.
• Arched dam.
• Gravity dam
• Resist the pressure of water by its weight.
• Construction of material used for his dam, is
  solid masonry or concrete.

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• Arch dam
• It resist the pressure of water partly due to its
  weight and partly due to arch action.
• Buttress dam
• Buttress supporting a flat slab.
• When cost of reinforced concrete is high such
  type of dam is selected.

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• Spillway
• Excess accumulation of water endangers the
  stability of dam construction. Also in order to
  avoid the over flow of water out of the dam
  especially during rainy seasons spillways are
  provided. This prevents the rise of water level
  in the dam.
• Spillways are passages which allows the excess
  water to flow to a storage area away from the
  dam.
• Gate
• A gate is used to regulate or control the flow of
  water from the dam.
• Pressure tunnel
• It is a passage that carries water from the
  reservoir to the surge tank.

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• Surge tank
• A Surge tank is a small reservoir or tank in
  which the water level rises or falls due to
  sudden changes in pressure.
• Purpose of surge tank
• To serve as a supply tank to the turbine when the
  water in the pipe is accelerated during increased
  load conditions and as a storage tank when the
  water is decelerating during reduced load
  conditions.
• To reduce the distance between the free water
  surface in the dam and the turbine, thereby
  reducing the water-hammer effect on penstock and
  also protect the upstream tunnel from high
  pressure rise.
• Water-hammer effect
• The water hammer is defined as the change in
  pressure rapidly above or below normal pressure
  caused by sudden change in the rate of water flow
  through the pipe, according to the demand of
  prime mover i.e. turbine

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• 4- Water Ways.
• Water ways are the passages, through which the
  water is conveyed to the turbines from the dam.
  These may include tunnels, canals, flumes,
  forebays and penstocks and also surge tanks.
• A forebay is an enlarged passage for drawing the
  water from the reservoir or the river and giving
  it to the pipe lines or canals.

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Penstock thickness

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Number of penstock

• A hydro Power Plant uses a number of turbine
  which are to be supplied water through penstock.
• To use a single penstock for the whole a plant.
• To use on penstock for each turbine separately.
• To provide multiple penstock but each penstock
  supplying water to at least two turbine.
• Factors for Selecting number of penstocks
• Economy.
• Operational safety.
• Transportation facilities.

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• 5- Power House.
• The power house is a building in which the
  turbines, alternators and the auxiliary plant are
  housed. Some important items of equipment
  provided in the power house are as follows
• Turbines
• Generators
• Governors
• Relief valve for penstock setting
• Gate valve
• Transformer
• Switch board equipment and instruments
• Oil circuit breaker
• Storage batteries
• Outgoing connections
• Cranes
• Shops offices

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• The surface power house has been broadly divided
  into three subdivisions which is separated
• from the intake as mentioned below
• Substructure
• Intermediate structure
• Super-structure.

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• Draft tube
• It is connected to the outlet of the turbine.
• It allows the turbine to be placed above the tail
  water level.
• 6- Tail water level or Tail race
• Tail water level is the water level after the
  discharge from the turbine. The discharged water
  is sent to the river, thus the level of the river
  is the tail water level.
• Electric generator, Step-up transformer and Pylon
  
• As the water rushes through the turbine, it spins
  the turbine shaft, which is coupled to the
  electric generator. The generator has a rotating
  electromagnet called a rotor and a stationary
  part called a stator. The rotor creates a
  magnetic field that produces an electric charge
  in the stator. The charge is transmitted as
  electricity. The step-up transformer increases
  the voltage of the current coming from the
  stator. The electricity is distributed through
  power lines also called as pylon.

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Classification of hydro-Electric power plant

• The classification of hydro electric power plant
  depend on the following factors
• Quantity of water
• It is following types.
• Run of river plant.
• Storage plant.
• Pumped storage.
• Availability of Head of Water
• Low head plant. Operating head lt 15m.
• Medium head plant. Operating head 15 to 50m.
• High head plants Operating head gt 50m.

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a) Low head plant

• Operating head is less than 15m.
• Vertical shaft Francis turbine or Kaplan turbine.
• Small dam is required.

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a) Medium head plant

• Operating head is less than 15 to 50m.
• Francis turbines.
• Forebay is provided at the beginning of the
  penstock.

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a) High head plant

• Operating head exceed 50m.
• Pelton turbines.
• surge tank is attached to the penstock to reduce
  water hammer effect on the penstock.

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• Advantages of hydel power plant
• Water is a renewable energy source.
• Maintenance and operation charges are very low.
• The efficiency of the plant does not change with
  age.
• In addition to power generation, hydro-electric
  power plants are also useful for flood control,
  irrigation purposes, fishery and recreation.
• Have a longer life(100 to 125 years) as they
  operate at atmospheric temperature.
• Water stored in the hydro-electric power plants
  can also be used for domestic water supply.
• Since hydro-electric power plants run at low
  speeds(300 to 400 rpm) there is no requirement of
  special alloy steel construction materials or
  specialised mechanical maintenance.

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• Disadvantages of hydel power plant
• The initial cost of the plant is very high.
• Since they are located far away from the load
  centre, cost of transmission lines and
  transmission losses will be more.
• During drought season the power production may be
  reduced or even stopped due to insufficient water
  in the reservoir.
• Water in the reservoir is lost by evaporation.

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• Draft Tube
• Reaction turbines must be completely enclosed
  because a pressure difference exists between the
  working fluid (water) in the turbine and
  atmosphere. Therefore, it is necessary to connect
  the turbine outlet by means of a pipe known as
  draft tube upto tailrace level.
• Types of Draft Tubes
• Conical Draft Tube.
• This is known as tapered draft tube and used in
  all reaction turbines where conditions permit. It
  is preferred for low specific speed and vertical
  shaft Francis turbine. The maximum cone angle of
  this draft tube is limited to 8 (a 4). The
  hydraulic efficiency of such type of draft tube
  is 90.

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• 2- Elbow Type Draft Tube.
• The elbow type draft tube is often preferred in
  most of the power plants, where the setting of
  vertical draft tube does not permit enough room
  without excessive cost of excavation.
• 3- Moody Draft Tube.
• This draft tube has an advantage that its conical
  portion at the center reduces the whirl action of
  water moving with high velocity centre reduces.

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Hydraulic Turbines

• Advantages
• Simple in construction.
• Easily controllable.
• Efficient.
• Ability to work at peak load.
• Work on load variation.
• Start from cold conditions pick up load at
  short time.
• Types of turbines
• Impulse
• Reaction

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• Impulse Turbine
• The passages are not completely filled, water
  acting on a wheel buckets is at atmospheric
  pressure and is supplied at few points at the
  periphery of wheel kinetic energy is supplied
  to the wheel.
• Casing
• Penstock
• Nozzle
• Runner
• Buckets
• Needle Valve
• shaft

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• Reaction Turbine
• Water passages are completely filled with water,
  water acting on wheel vanes is under pressure
  greater than atmospheric, water enter all around
  the periphery of wheel and energy is in the form
  of both pressure kinetic energy is utilized by
  the wheel.
• Essential parts
• Spiral casing
• Guide wheel
• Runner
• Draft tube
• Horizontal shaft type or vertical shaft type
  turbine
• Low medium head turbines

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Direction of flow of water

• Tangential flow turbine
• Radial flow turbine.
• Axial flow turbine.
• Mixed flow turbine.

Types of turbine Flow direction
Kaplan turbine Axial flow
Franics Turbine Radial inward or mixed flow
Pelton wheel Tangential flow
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Position of shaft

• Vertical shaft turbine.
• Horizontal shaft turbine.
• Head of water
• High head turbines.
• Medium head turbines.
• Low head turbines.
• Impulse turbines high head.
• Reaction turbines low medium heads.

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• Performance of water turbine
• Important parameter for any particular turbine
  are
• Discharge
• Head
• Efficiency
• Speed
• Power
• The turbine characteristic like unit power, unit
  speed unit discharge help in studying the
  performance of turbines.

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• Specific Speed
• The specific speed of a turbine is defined as the
  speed at which the turbine runs developing one
  B.H.P. under a head of one meter.
• The equation for the specific speed of a turbine
  can be obtained by using the principle of
  similarity.
• where D and N are diameter and speed of a turbine
  and H is the head acting on the turbine.
• where B is the height of the blade and Vf is the
  velocity of flow.
• Substituting the value of D in the above
  equation.

where P is the power developed.
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• Substituting the value of Q in the above
  equation, we get
• where C is constant depending upon the type of
  the turbine.
• If the turbine develops 1 B.H.P. under one meter
  head then
• C N N.
• where Ns is the specific speed as per the
  definition.
• Substituting the value of C in the above
  equation, we get

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SELECTION OF SITE FOR A HYDRO-ELECTRIC POWER PLANT

• The following factors should be given careful
  consideration
• while selecting a site for a hydro-electric power
  plant
• 1. Water Available.
• The recorded observation should be taken over a
  number of years to know within reasonable, limits
  the maximum and minimum variations from the
  average discharge. the river flow data should be
  based on daily, weekly, monthly and yearly flow
  ever a number of years. Then the curves or graphs
  can be plotted between tile river flow and time.
  These are known as hygrographs and flow
• duration curves.

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• 2. Water-Storage.
• The output of a hydropower plant is not uniform
  due to wide variations of rain fall. To have a
  uniform power output, a water storage is needed
  so that excess flow at certain times may be
  stored to make it available at the times of low
  flow. To select the site of the
• Dam, careful study should be made of the geology
  and topography of the catchment area to see if
  the natural foundations could be found and put to
  the best use.
• 3. Head of Water.
• The level of water in the reservoir for a
  proposed plant should always be within limits
  throughout the year.

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• 4. Distance from Load Center.
• Most of the time the electric power generated in
  a hydro-electric
• power plant has to be used some considerable
  distance from the site of plant. For this reason,
  to be economical on transmission of electric
  power, the routes and the distances should be
  carefully considered since the cost of erection
  of transmission lines and their maintenance will
  depend upon the route
• selected.
• 5. Access to Site.
• It is always a desirable factor to have a good
  access to the site of the plant. This factor is
  very important if the electric power generated is
  to be utilized at or near the plant site. The
  transport facilities must also be given due
  consideration.

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Hydrology

• It is natural science that deal with the
  distribution of water on land beneath the surface
  of earth.
• It deal with the solid, liquid vapour forms of
  water.
• Hydrologic cycle
• The various processes involved in the transfer of
  moisture from the sea to the land and back to the
  sea again constitute which is called hydrologic
  cycle.
• Hydrologic eq. is expressed as follows
• P R E
• Where,
• P perspiration
• R Run-off
• E Evaporation.

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• Perspiration
• It includes all the water that falls from atm. To
  the earth surface. Mostly perspiration is of two
  types.
• Liquid perspiration (rainfall)
• Solid perspiration (Snow, Hail storm)
• Run-off
• It is that portion of the perspiration which
  makes its way towards stream, lakes or ocean.
• Run-off occur only if the rate of perspiration
  exceed the rate at which water infiltrate into
  the soil after depression small and large on
  the soil surface get filled in the water.
• Evaporation
• Transfer of water from liquid to vapour state
• Transpiration
• Process by which water is released to the
  atmosphere by the plant.

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Assignment

• Topics 6.37 6.38(6.38.1, 6.38.2, 6.38.3,
  6.38.4)
• Examples
• 6.1 to 6.13, 6.15 to 6.20.

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Questions?