hydro electric power station - 123seminarsonly.com · 2013-02-20 · hydro electric power station...
TRANSCRIPT
Hydro electric power station • a generating station which utilizes the potential energy of water at a high level for generation of electrical energy is known as hydro-electric power station.
• water head is created by constructing a dam across a river or lake.
• water is led to water turbine
• potential
• energy is converted into kinetic energy
• kinetic energy is converted to the mechanical energy by allowing the water to flow through the hydraulic turbine runner
• becoming more popular because limited oil reserves
• importance due to flood control, storage of water for irrigation, and water for drinking.
• The generation of electric energy from falling water is only a small process
-Hydrological cycle” or rain evaporation cycle”
This cycle is shown in figure.
• The input to this cycle is the solar energy.
• Due to this, evaporation of water takes.
• On cooling, these water vapours form clouds. Further cooling makes the clouds to fall down in the form of rain, and snow etc; known as precipitation
• Before a water power site is considered for development, the following factors must be thoroughly analyzed
-1. The capital cost of the total plant.
-2. The capital cost of erecting and maintaining the transmission lines and the annual power loss
-3. The cost of electric generation compared with steam, oil or gas plants which can be conveniently set up near the load center.
• Inspite of the above factors, following advantages which make these suitable for large interconnected electric system:
-1. The plant is highly reliable and its maintenance and operation charges are very low.
-2. The plant can be run up and synchronized in a few minutes.
-3. The load can be varied quickly and the rapidly changing load demands can be met without
any difficulty.
-4. The plant has no stand by losses. -5. No fuel charges. -6. The efficiency of the plant does not change
with age. -7. The cost of generation of electricity varies
little with the passage of time. • the hydro-electric power plants have the
following disadvantages also: -1. The capital cost of the plant is very high. -2. The hydro-electric plant takes much longer in
design and execution. -3. These plants are usually located in hilly areas
far away from the load center. -4. Transformation and transmission costs are
very high.
-5. The output of a hydro-electric plant is never constant due to An unpredictable change of
monsoons(A seasonal wind in southern Asia; blows from the southwest (bringing rain) in summer and from the northeast in winter) and their dependence on the rate of water flow in a river.
RUN-OFF -Defined as the total condensation of moisture that
reaches the earth in any form • includes all forms of rains, ice, and snow etc -Run-off = Total precipitation – Total evaporation • The unit of run-off are m3/s • Day-second meter • Rain-fall is measured in terms of centimeters of water
over a given area and over a given period (usually one year). • The portion of the total precipitation that flows
through the catchment area is known as “Run-off”. • The catchment area of a hydro site is the total area
behind the dam, draining water into the reservoir.
Factors Affecting Runoff 1.Nature of Precipitation
-Rains lasting a longer time results in larger run-off
-Humid atmospheres
2.Topography of Catchments Area
-Steep,
- The water will flow quickly and absorption and evaporation losses will be small
3.Geology of Area
-Rocky areas will give more run-off
4.Meteorology.
-Run-off increases with low temperature,
5.Vegetation.
-Evaporation and seepage are increased by cultivation
6.Size and Shape of Area.
- Large areas will give more run-off
HYDROGRAPH AND FLOW DURATION CURVE
• A hydrograph indicates the variation of discharge or flow with time.
• It is plotted with flows as
• ordinates and time intervals as abscissas.
• The flow is in m3/sec and the time may be in hours, days, weeks or months
THE MASS CURVE
• Indicates total volume of run-off in cubic meters upto a certain time.
• Or the mass curve is to compute the capacity of the reservoir for a hydro site.
• Abscissa can be day, month or year and cumulative volume of flow as ordinate
Storage of water
• Wide variations in flow of
• In order to ensure generation throughout the year.
Pondage
• Power demand fluctuates with time
• If power plant is away from reservoir
• Capacity of pond should be sufficient to coup with hourly changes for 24 hour.
ESSENTIAL FEATURES OF A WATER-POWER PLANT
• 1. Catchment area.
• 2. Reservoir.
• 3. Dam and
intake house.
• 4. Inlet water way.
• 5. Power house.
• 6. Tail race or
outlet water way.
2. Reservoir. -The purpose of the storing of water in the reservoir is to get a uniform power
output throughout the year 3. Dam -Are built to create head • Head -Water must fall from a higher elevation to a lower one to release its stored
energy. -The difference between these elevations (the water levels in the forebay and
the tailbay) is called head -high-head (800 or more feet) -medium-head (100 to 800 feet) low-head (less than 100 feet) 4. Inlet water way -the passages, through which the water is conveyed to the turbines from the
dam. tunnels, canals, forebays and penstocks and also surge tanks. - A forebay is an enlarged passage for drawing the water from the reservoir -Tunnels are of two types: pressure type and non-pressure type.
• 6. Tail Race or Outlet Water Way
-Tail race is a passage for discharging the water leaving the turbines
Constituents of hydro electric power plant
• Spillways
-when river flow exceeds the storage limits
• Surge tanks
-pipe to absorb sudden rises of pressure as well as to quickly provide extra water during a brief drop in pressure
-at high or medium head
• Penstocke
-A gate that controls water flow, or an enclosed pipe that delivers water to hydraulic turbines
-concrete: less than 30m
-steel : any head
-thickness increases with head or working pressure
Classification of Hydro Turbines
• Reaction Turbines – Derive power from pressure drop across turbine
– Totally immersed in water
– Angular & linear motion converted to shaft power
– Propeller, Francis, and Kaplan turbines
• Impulse Turbines – Convert kinetic energy of water jet hitting buckets
– High heads
– No pressure drop across turbines
– Pelton, Turgo, and crossflow turbines
Turbine Design Ranges
• Kaplan
• Francis
• Pelton
• Turgo
2 < H < 40 10 < H < 350 50 < H < 1300 50 < H < 250 (H = head in meters)
Efficiency of Hydropower Plants
• Hydropower is very efficient
– Efficiency = (electrical power delivered to the “busbar”) ÷ (potential energy of head water)
• Typical losses are due to
– Frictional drag and turbulence of flow
– Friction and magnetic losses in turbine & generator
• Overall efficiency ranges from 75-95%
Examples • A hydro electric generating station is supplied
from a reservoir of capacity 5*106m3/sec at head of 200meters. Find the total energy available in kWh if the overall efficiency is 75%.
Solution.
Q= 5*106m3/sec
H= 200meters
Efficiency= 75%
W=(5*106)(1000), (mass of 1m3 of water is 1000kg)
Electrical energy available=W*H*efficiency, watt-sec
Ex: it has been estimated that the min run off of approximately 94m3/sec will be available at a hydro electric project with head of 39m. Determine(1) firm capacity (2) yearly gross o/p. assume efficiency of the plant to be 80%
Sol:
Weight of water available, W=94*1000=94000kg/sec, Head=39m
Work done per sec=w*H=94000*9.81*39=35963kW
(1)Firm capacity=plant efficiency*gross plant capacity=0.8*35963=28770kW
(2)Yearly gross o/p=28770*8760=252*106kWh