Classification of Hydroelectric power plants

1. Chapter Two
Chapter Two
Classification of Hydroelectric Power Plants
By Yimam A.(MSc.)
December 16, 2020
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2. Chapter Two
Outline
1 Classification based on quantity of water available
2 Classification based on the availability of head of water
3 Classification according to the nature of load
4 Classification based on transmission system (interconnection)
5 Classification based on plant capacity
6 Classification according to purpose
7 Classification according to hydrological relation
8 Classification according to turbine characteristic i.e. specific speed.
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3. Chapter Two
Learning Objectives
At the end of this chapter the students should be able to:
Understand the classification of hydroelectric power plants based on quantity of water
available (water flow regulation), availability of head, power plant capacity, nature of
load characteristics, transmission system(interconnection), purpose, hydrological
relation.
Categorize the existing hydroelectric power plants in Ethiopia based on the above
classification.
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4. Chapter Two
Classification based on quantity of water available
Classification based on quantity of water available
The classification of hydroelectric power plants based on quantity of water available
(water flow regulation) is:
Run off river plants without pondage
Run off river plants with pondage
storage type plants(Impoundment plants)
Pumped storage plants
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5. Chapter Two
Classification based on quantity of water available
Run off river plants without pondage
Run off river plants without pondage
It doesn’t store water and uses as the water comes.
There is no control on flow of water so that during high floods or low loads water is
wasted while during low run off the plant capacity is considerably reduced.
Generating capacity primarily depending on the rate of flow of water.
During dry periods the power production will be very poor, since the water flow rate
will be low.
Due to non uniformity of supply and lack of assistance from a firm capacity the
utility of these plants are much less than those of other types.
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6. Chapter Two
Classification based on quantity of water available
Run off river plants with pondage
Run off river plants with pondage
Pondage: the collection of water behind a dam at the plant and increases the stream
capacity for a short period say a week.
Storage: collection of in up stream reservoirs and this increases the capacity of the
streams over an extended period of several months.
Usefulness of run off river is increased by pondage.
These plants may work satisfactorily as base load and peak load plants.
As compared to that without pondage, it is more reliable and its generating capacity
is less dependent on the flow rates of water available.
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7. Chapter Two
Classification based on quantity of water available
Storage type plants (Impoundment plants)
Storage type plants (Impoundment plants)
This type of plant, water is stored behind the dam and water is available throughout
the year even in dry season.
Storage type plant is one with reservoir of sufficiently large size to permit carry over
storage from the wet season to the dry season and thus to supply firm flow
substantially more the minimum natural flow.
This plant can be used as base load plant as well as peak load plant as water is
available with control as required.
The majority of hydroelectric power plants in our country are of this type.
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8. Chapter Two
Classification based on quantity of water available
Pumped storage plant
Pumped storage plant
Are employed at the places where the quantity of
water available for power generation is inadequate.
Water passing through the turbine is stored in the tail race pond.
During low load periods this water is pumped back to the head reservoir, which can
be used during peak load plants.
This water can be again used for generating power during peak load periods.
Pumping of water may be done seasonally or daily depending upon the conditions of
the site and the nature of the load on the plant.
Usually interconnected with steam or diesel power plants.
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9. Chapter Two
Classification based on quantity of water available
Pumped storage plant
Cont.....
Figure: Pumped storage plant
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10. Chapter Two
Classification based on quantity of water available
Pumped storage plant
Cont.....
The water leaving the turbines of hydro electric power plant is stored in tail-race
pond.
This water is pumped back to the head race reservoir by means of reversible pump
turbine sets and is used for power generation at the peak load time.
Pumped storage plants are generally inter connected with other plants such as steam
power plants.
The off peak capacity of steam power station can be used for pumping water in the
head reservoir.
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11. Chapter Two
Classification based on quantity of water available
Pumped storage plant
Cont.....
Advantages of pumped storage plants are as follows:
The capital cost of pumped storage plant is low as compared to other peaking units.
There is a great deal of flexibility in the operational schedules of the system.
A pumped storage plant can pick up load rapidly and is dependable.
They operate at higher load factors and improve the overall efficiency of the system.
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12. Chapter Two
Classification based on the availability of head of water
Classification based on the availability of head of water
The difference in elevations between the water level in forebay and tail bay is called
head.
Water must fall from a higher elevation to a lower one to release its stored energy.
Three categories of hydro power plant based on design head values are
High-head (100m and above)
Medium-head (30m to 100m)
Low-head (less than 30m)
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13. Chapter Two
Classification based on the availability of head of water
High head power plants
High head power plants
Figure: High head power plants
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14. Chapter Two
Classification based on the availability of head of water
High head power plants
Cont.....
A hydel plant with a water head of more than 100 meters is termed as a high head
plant.
The main dam, spillway, and power house stand at widely separated locations. Water
flows from the reservoir through a tunnel and penstock to the turbines.
In this case, the water from the main reservoir is carried through tunnels up to the
surge tank, from where it is taken through the penstock.
Since the water head is very high the effect of water hammer is too severe in such
plants, it is essential to provide a surge tank in the water line at appropriate location.
The surge tank takes care of the increasing and decreasing water levels during the low
demand and high demand periods, respectively.
The Francis and Pelton wheel turbines are most suitable for high head plants.
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15. Chapter Two
Classification based on the availability of head of water
Medium head power plants
Medium head power plants
Figure: Medium head power plants
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16. Chapter Two
Classification based on the availability of head of water
Medium head power plants
Cont.....
A hydel plant with a water head of in the range of 30 to 100 meters is termed as a
medium head power plant.
The forebay provided at the beginning of the penstock serves as water reservoir.
The water is generally carried in open canals from main reservoir to the forebay and
then to the power house through the penstock.
The forebay itself acts as the surge tank, and hence receives the excess water during
the low demand periods.
This type of plant commonly uses Francis turbines.
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17. Chapter Two
Classification based on the availability of head of water
Low head power plants
Low head power plants
Figure: Low head power plants
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18. Chapter Two
Classification based on the availability of head of water
Low head power plants
Cont.....
A plant with a water head of less than 30 meters is termed a low head plant.
No surge tank is required for this plant, dam itself discharge the surplus water from
the river.
In such plants, a small dam is constructed across a river to obtain the necessary
water head.
The excess water is allowed to flow over the dam, while the water head is made use to
run a hydraulic turbine.
This type of plant uses vertical shaft Francis or Kaplan turbine.
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19. Chapter Two
Classification according to the nature of load
Classification according to the nature of load
1. Base load plants :
These plants are required to supply constant power in the grid.
They run continuously without any interruption and are mostly remote controlled.
Base load plants run throughout the year
They operate at high load factors
Hydropower plants with ample storage are used as base load plants. e.g. storage
plants, run-off river plants without pondage.
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20. Chapter Two
Classification according to the nature of load
Classification according to the nature of load
2. Peak load plants:
Plants which supply the power during peak loads are known as peak load plants.
They only work during certain hours of a day when the load is more than the average.
Peak load plants run for a few hours in the year and operate at low load factors. e.g.
pumped storage plants, run-off river plants with pondage.
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21. Chapter Two
Classification according to the nature of load
Cont....
Figure: Load duration curve
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22. Chapter Two
Classification based on transmission system (interconnection)
Classification based on transmission system (interconnection)
A Isolated (off-grid) power plants
Whenever a hydropower plant is set up in a remote area in order to meet the local
demands then such a hydropower plant is known as Isolated(off-grid) system.
B Interconnected (on-grid) power plants
Whenever the hydropower plant is set up to meet the demands of areas which are at a
fair distance from the plant, then the transmission of power takes through the grid
system. Such a setup is referred to as connected to grid.
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23. Chapter Two
Classification based on plant capacity
Classification based on plant capacity
I Large-hydro: > 100 MW feeding into a large electricity grid
II Medium-hydro: 15 - 100 MW usually feeding a grid
III Small-hydro:1 - 15 MW - usually feeding into a grid
IV Mini-hydro: 0.1 - 1 MW either stand alone schemes or more often feeding into the
grid.
V Micro-hydro: From 5 - 100 kW usually provided power for a small community or
rural industry in remote areas away from the grid.
VI Pico-hydro: < 5 kW remote areas away from the grid.
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24. Chapter Two
Classification according to purpose
Classification according to purpose
A Single Purpose:
When the whole soul purpose of a project is to produce electricity then such a project is
known as a single purpose hydro power project.
B Multi Purpose:
When the water used in hydropower project is to be used for other purposes is known as
multi purpose hydro power project.
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25. Chapter Two
Classification according to purpose
Cont....
Purpose of multipurpose hydro project
For generation of electricity.
For irrigation of agricultural land.
For navigation.
For fisheries and tourism.
For flood control.
For domestic water supply.
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26. Chapter Two
Classification according to hydrological relation
Classification according to hydrological relation
A Single Stage:
When the run off from a single hydropower plant is diverted back into river or for any
other purpose other than power generation, the setup is known as Single Stage.
B Cascade System:
When two or more hydropower plants are used in series such that the runoff discharge of
one hydro power plant is used as an intake discharge of the second hydro power plant
such a system is known as cascade hydropower plant.
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27. Chapter Two
Classification according to hydrological relation
Cont....
Figure: (a) single stage hydropower development scheme (b) cascade or multistage hydropowerBy Yimam A.(MSc.) Chapter Two December 16, 2020 27 / 29

28. Chapter Two
Classification according to turbine characteristic i.e. specific speed.
Cont....
Classification according to turbine characteristic i.e. specific speed.
i) High specific speed
ii) Medium specific speed.
iii) Low specific speed
Classification according to topography
i Low land
ii Hilly area
iii Mountainous region
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29. Chapter Two
Questions
Thank You!
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