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  1. 1. What is Hydroelectric Power?  Hydroelectricity is a term referring to the electricity generated by hydro power  A hydropower development is essentially to utilize the hydraulic power possessed by the water flowing in a stream and to develop from it electric power through hydraulic turbines coupled to electric generators  The total amount of hydroelectric power that would be made available from a stream depends on continuous flow rate of the stream and the head possessed by the flowing water
  2. 2. Lay out of typical hydroelectric power scheme
  3. 3. Comparison of Hydroelectric and Thermal Power Plants Criterion Hydroelectric Power Plant Thermal Power Plant 1. Initial cost and life expectancy Higher initial cost due to costly infrastructure such as dam, spillway, et., and its location at a place far off from the consumer or load centre Lower initial cost due to its proximity to consumer or load centre Higher life expectancy, may be about 50 years Lower life expectancy 2. operation, maintenance and repair (OMR) cost Low OMR cost due to no fuel cost High OMR cost due to costly fuel and the cost of fuel transport Less maintenance and repair cost and staff needed for operation is less High maintenance and repair cost and staff needed for operation is more Water is replenished every year an put to non-consumable use. However, supply of water may be erratic year after year Non-replenishable source Low taxes due to its location in remote areas High taxes due to its location near cities
  4. 4. Criterion Hydroelectric power plant Thermal power plant 3. Transmission losses More due to long transmission lines Less due to short transmission lines 4. Pollution No problem of pollution or ecological unbalance later Causes air pollution as well as stream pollution resulting in ecological imbalance unless cooling towers or cooling ponds are provided No waste product and hence no problem of its disposal Problem of haulage and disposal of waste product viz., smoke, ash etc. 5. Actuating time A few seconds to 3 to 4 minutes depending on the length of conduit About 30 minutes Quite suitable to take up peak load Not suitable for use as peak load plants
  5. 5. Selection of Suitable Types of Turbines S.No Head in meters Type of turbine Specific speed 1 300 or more Pelton wheel, single or multiple jet 8.5 to 47 2 150 to 300 Pelton or Francis 30 to 85 3 60 to 150 Francis or Deriaz 85 to 188 4 Less than 60 Kaplan or Deriaz 188 to 860
  6. 6. Advantages of Hydroelectric Power Fuel is not burned so there is minimal pollution Water to run the power plant is provided free by nature Hydropower plays a major role in reducing greenhouse gas emissions Relatively low operations and maintenance costs The technology is reliable and proven over time It's renewable - rainfall renews the water in the reservoir, so the fuel is almost always there
  7. 7. Disadvantages of Hydroelectric Power High investment costs Hydrology dependent (precipitation) In some cases, inundation of land and wildlife habitat In some cases, loss or modification of fish habitat Fish entrainment or passage restriction In some cases, changes in reservoir and stream water quality In some cases, displacement of local populations
  8. 8. Classification of Hydel Plants 1. Classification based on storage characteristics  Run-off river plants - Utilize the minimum flow of a river - Do not have appreciable storage on the u/s side - Suitable only on perennial rivers
  9. 9.  Storage plants - It has an upstream storage reservoir - Continuous firm power generation is possible  Pumped storage plants - Power is generated during peak hours, but during off-peak hours water is pumped back from the tail water pool to head water pool for future use - Primarily meant for assisting an existing thermal or other hydel plant
  10. 10.  Tidal plants - Works on the principle that there is a rise in sea water during high tide period and fall during the low ebb period - The tidal range, i.e. the difference between high and low tide levels is utilized to generate power
  11. 11. 2. Classification according to functional basis  Base load plants - These are the plants which are capable of substantially continuous operation in the base of the load curve throughout the year  Peak load plants - It is a hydel plant designed and constructed primarily for taking care of the peak load of a power system 3. Classification based on the basis of head  Micro head plants – H = 10 m to 20 m  Low head plants – H <= 30 m  Medium head plants – H = 30 m to 250 m  High head plants – H > 250 m
  12. 12. Important Terms Connected With Hydropower  Water Power Potential - It is the amount of power generated when Q cumecs of water is allowed to fall through a head difference of H meters and is given by: P = η γ Q H  Normal Water Level (NWL) - It is the highest elevation of water level that can be maintained in the reservoir without any spillway discharge  Minimum Water Level (MWL) - It is the elevation of the water level which produces minimum net head on the power units (i.e. 60% of the design head)
  13. 13.  Rated Head – The head at which the turbine functioning at full gate opening will produce a power output, equal to that specified on the name plate of the turbine.  Gross Head – It is the difference in water level elevation at the point of diversion of water for the hydel scheme and the point of return of water back to the river.  Operating Head – It is the difference between the elevation of water surface in the fore-bay and the tailrace after making due allowance for approach and exit velocity heads  Net Head or Effective Head – It is the difference of head at the point of entry and exit of turbine and includes the respective velocity and pressure heads at both places
  14. 14.  Installed Capacity – It is the total capacity in kilowatts or million kilowatts of all the turbine generator units installed in a power house.  Dependable Capacity – It is the load carrying capability of the power house with respect to the load characteristics during a specified time interval  Load Factor (LF) – It is defined as the ratio of the average load over a certain period of time to the peak load during the same period  Utilization Factor (UF) or Plant Use Factor Average load over a certain period Peak load during that period Load Factor  Water actually utilized for power production Water available in the river UF 
  15. 15.  Capacity Factor or Plant Factor – It is the ratio of average output of the plant for a given period of time to the plant capacity or, it can also be defined as:  Firm Power – The net amount of power which is continuously available from a plant without any break on firm or guaranteed basis.  Secondary Power – The excess power available over the firm power during the off peak hours or during monsoon season  Power Factor – It is the ratio of actual power in kilowatts to the apparent power in kilo volt amperes (KVA) Energy actually produced in a given time Max. energy that can be produced by the plant during the same time CF 
  16. 16. Principal Components of a Hydroelectric Scheme  The fore-bay  Intake structure  Penstocks  Surge tank or surge chambers  Turbines  Power house  Draft tube  The tailrace
  17. 17. Components of a Hydroelectric Power Plant
  18. 18. 1. Forebay  An enlarged body of water provided just in front of the penstock  It is provided in the case of run-of-river plants and storage plants when the power house is located far away from the dam  The main function of forebay is to provide a small balancing storage upstream of the power house 2. Intake structures  The water from the reservoir or forebay is let into the penstocks through intake structure  The main components of an intake structure are trash racks and gates  Trash rack is provided to prevent the entry of debris into the water passage of hydropower plant  The gates are provided to control the entry of water into the penstocks
  19. 19. 3. Penstocks  Penstocks are the pipes of large diameter used for conveying water from the reservoir to the turbines  A sufficient water depth should be provided above the penstock entrance to avoid formation of vortices which may carry air into the penstock and result in lowered turbine efficiency and undesirable pressure surges 4. Surge tanks  A surge tank is a cylindrical open-topped storage tank which is connected to the penstock at a suitable point.  These are provided to relieve the penstocks of excess pressure caused by water hammer  They also provide additional supply of water when the turbines are in need of more water on account of increased load  A surge tank should be provided as close to the power house as is possible
  20. 20. 4. Power house  It is a structure which houses the various hydraulic and electric equipment  The various hydraulic equipments are turbines, gates or gate valves, governors, etc.  The various electrical equipments are, generators, transformers, switching equipments, transmission lines and transmission structures 5. Turbines  The machine which converts hydraulic energy to mechanical energy, and finally to electrical energy 6. Tail race  A channel into which the water is discharged after passing through the turbines 7. Draft tube: - An elongated pipe connecting turbine to tail race
  21. 21. Example Problems Example 1: Three turbo-generators each of capacity 10000 kW have been installed at a hydel power station. During a certain period of load, the load on the plant varies from 12000 kW to 26000 kW. Calculate (i) total installed capacity, (ii) load factor, (iii) plant factor and (iv) utilization factor. Example 2 : During a low water week a river has an average daily flow of 32 m3/sec with a fluctuation during the day requiring a pondage capacity of approximately 15% of the daily discharge. a HEP is to be located on the river which will operate 5 days a week, 24 hours a day, but will supply power at varying rate such that the daily load factor is 55% corresponding to which the pondage required is equal to 0.2 times the mean flow to the turbine. On Saturday and Sunday all the flow is ponded for use on rest of the days.
  22. 22. Contd. If the effective head on the turbines when the pond is full is to be 25 m and the maximum allowable fluctuation in pond level is 1 m find (a) the surface area of the pond to satisfy all the operating conditions, (b) the weekly output at the switch board in kwh. Assume turbine efficiency 55% and generator efficiency 92%