For civil Engineers

1. Hydropower
Salik Haroon Abbasi
Civil Engineer U.E.T Lahore

2. Hydraulic Structures Fourth Edition
P. Novak, A.I.B. Moffat and C. Nalluri
School of Civil Engineering and
Geosciences,
University of Newcastle upon Tyne, UK
R. Narayanan
Formerly Department of Civil and
Structural Engineering, UMIST,
University of Manchester, UK
Reference:

3. Hydropower
Hydropower is extracted from the natural
potential of usable water resources, and
about 20% of the world’s power
requirement is at present derived in this
way

4. Any water resources development of which a hydropower scheme may
form part has environmental and social impacts, which must be taken into
consideration at the initial planning stage. Also, legal and political
implications must be carefully considered.
One of the most important factors affecting any hydropower
development is the cost of the scheme. With the rising costs and shortage
of resources, economic comparisons with various energy sources – oil,
coal, nuclear, gas and other renewable energy resources have to be made.
In this, the fact that, unlike the ‘fuel’ costs of the hydropower plant, the
costs of fuel for power generation by a conventional thermal plant rise at
least with inflation makes hydroelectric plants economically
advantageous, particularly in the long term.

5. Power Demand
The power demand is defined as the total load which consumers
choose, at any instant, to connect to the supplying power system.
The system should have enough capacity to meet the expected
demand, in addition to unexpected breakdowns and maintenance
shutdowns

6. Base load
Base Load is the load continuously exceeded
Average load
Average load is the area under the curve divided by the time.
The load factor
The load factor over a certain period is the ratio of the average load to the
peak load and is expressed as a daily, weekly, monthly or yearly value.
It must be appreciated that low load factors represent a degree of
inefficiency, as sufficient capacity in the form of generating machinery

7. A typical demand curve

8. Power Generation Pattern of the
Pakistan (2004)
Access of population to electricity in Pakistan = 62%

9. Classification of Energy Resources
Renewable Energy: These are sources of energy produced continuously
in nature and will not get exhausted eventually in future. e.g., Hydel
Energy, Solar Energy, Tidal Energy, Geo-thermal Energy and Biomass.
Non-Renewable Energy: These are sources will get exhausted
eventually in future. e.g., Energy from Fossil Fuel.
Conventional Energy: Fossil Fuels, Hydel Power, Nuclear Energy Non-
Conventional Energy: Solar Energy, Wind Energy, Tidal Energy, Ocean
Thermal Energy, Geothermal Energy and Biomass. Commercial
Energy: Coal, oil, gas, Hydel Energy, Nuclear Non-
Commercial Energy: Wood, wastes etc

10.  Based on net yield of energy:
 Primary Energy Source: The energy source which provides a net
source of energy.
E.g. coal, natural gas, uranium, oil.
 Secondary Energy Source: From this source, the yield of energy is
less than input.
E.g. Solar, Wind, Tidal, Water Energy.
 Supplementary Energy Source: If the net energy yield provided by
the energy source is zero, it is called supplementary energy source.
E.g. thermal insulation.

11. Some fundamental definitions
The gross head, H0
The gross head, H0, at a hydroelectric plant is the difference in water level
between the reservoir behind the dam and the water level in the tail race.
The effective or net head
The effective or net head, H, is the head available for energy production after
the deduction of losses in the conveying system of the plant
The water falling from a high-level source drives turbines, which in turn drive
generators that produce the electricity. The hydraulic power is given by
PgQH/1000 (kW)

12. The hydraulic efficiency of the plant
The hydraulic efficiency of the plant is the ratio of net head to gross
head (i.e. H/H0)
Overall efficiency
The overall efficiency is equal to the hydraulic efficiency times the efficiency of
turbine and generator
The installed capacity of a hydroplant
The installed capacity of a hydroplant is the maximum power which can be
developed by the generators at normal head with full flow.

13. The unit of electrical power is the kilowatt, and that of the electrical
energy, defined as the power delivered per unit time, is the kilowatt-
hour (kWh).
Primary, or ‘firm’, power
Primary, or ‘firm’, power is the power which is always available, and which
corresponds to the minimum streamflow without consideration of storage
. Secondary, or surplus, power
Secondary, or surplus, power is the remainder and is not available all the time..
Secondary power is useful only if it can be absorbed by relieving some
other station, thus affecting a fuel (thermal) saving or water saving (in
the case of another hydrostation with storage).

14. Hydropower plants capture the energy of fallingwaterto
generate electricity. A turbineconvertsthe kinetic energy of
falling water into mechanical energy. Then a generator
converts the mechanical energy from the turbine into
electrical energy

16. Essential Elements of Hydropower Station
 Interception of water
 Conveyance of water
 Power Station
 Safe Disposal of used water
 Transmission of electricity
 Best conversion rate (~90%) due to the direct transformation of hydraulic forces
to electricity

17. Types of Hydropower
 Run-of-River Plant (Local Development)
 A weir or barrage is built across the river and the low head is used to
generate power.
 It has very limited storage capacity and can only use water when
available
 Its firm capacity is low, because water supply is not uniform throughout
the year, but it can serve as a base load plant

19. (b) Diversion canal plant
Sometimes topographic, geological and hydrological conditions and
environmental and economic considerations may favour diversion-type
power development schemes. The flow from the impounded water in the
river upstream of the barrage is diverted into a power canal which rejoins
the river further downstream (Fig.12.3), with the power station located
either next to the intake, or within the canal, or at the outlet. A rocky
stretch of the river containing rapids, where regulation could be difficult,
may be avoided by this type of layout. A fall of considerable height can be
developed by means of a diversion canal in a river valley with a relatively
steep slope.

20. Diversion canal plant

21.  Storage Plant
 The dam structure is separated from the power station by a
considerable distance over which the water is conveyed, generally by
a tunnel and pipeline, so as to achieve medium or high heads.
 The reservoir storage upstream of the dam increases the firm
capacity of the plant substantially, depending upon the run-off and
power requirements.
 The plant may be used as a base-load and/or peak-load installation.

22. Storage plant layouts (remote type)

23. Pumped storage plant
Where the natural annual run-off is insufficient to justify a conventional
hydroelectric installation, and where it is possible to have reservoirs at the head-
and tailwater locations, the water is pumped back from the lower to the headwater
reservoir. This kind of plant generates energy for peak load, and at off-peak
periods water is pumped back for future use. During off-peak periods excess
power available from some other plants in the system (often a run-of-river,
thermal, or tidal plant) is used in pumping the water from the lower reservoir.
A pumped storage plant is an economical addition to a system which
increases the load factor of other systems and also provides additional
capacity to meet the peak loads

24. Pumped storage plant

26. Head classification of hydropower plants
(a) Low-head plants
These plants have a gross head of less than about 50m and are usually of the run-
of-river type, with or without pondage, the power house being an integral part of
the dam or barrage. Tidal power plants are also low-head plants. The discharges
are usually large in low-head plants
(a) Medium-head plants
These plants may be either locally or remotely controlled, with a head of about
50–300m, and some of the well known large medium-head
(a) High-head plants
Most of the high head plants (head#300m) are of the remote-controlled type

27. Streamflow data essential for the assessment of water-power
potential
The gross head of any proposed scheme can be assessed by simple surveying
techniques, whereas hydrological data on rainfall and run-off are essential in
order to assess the available water quantities The following hydrological data
are necessary: (a) the daily, weekly or STREAMFLOW DATA
monthly flow over a period of several years, to determine the plant capacity
and estimated output which are dependent on the average flow of the
stream and its distribution during the year; (b) low flows, to assess the
primary, firm, or dependable power.

28. Streamflow data analysis
A typical streamflow hydrograph, including a dry period from which the
frequency of occurrence of a certain flow during the period can be calculated
The flow duration curve is a plot of the streamflow in ascending or
descending order (as ordinate) and its frequency of occurrence as a
percentage of the time covered by the record (as abscissa). Losses due to
evaporation and leakage from the proposed reservoir, and flow rates relating
to low-water management downstream of the reservoir and to any other
water demand, have to be taken into account in arriving at the regulated flow
duration curve.

30. Power duration curve
If the available head and efficiency of the power plant are known, the flow
duration curve may be converted into a power duration curve by changing
the ordinate to the available power (i.e. gQH).
The power which is available for 95% to 97% of the time on the reservoir
regulated schemes is usually considered to be the primary or firm power, and the
area of the power duration curve under the minimum amount of flow available
for 95% to 97% of the time thus gives the total amount of the primary power.
Primary power is not necessarily produced continuously

31. Flow–power duration curve (power scale multiplying factor

32.  Mass Curve: is the curve of accumulated total inflow
against time.
 Demand Curve: is the curve of accumulated total demand
against time.

33. The specific speed, Ns
. It is defined as the speed at which a geometrically similar runner would
rotate if it were so proportioned that it would develop 1kW when
operating under a head of 1m, and is given by
Ns NP1/2/H5/4
where N is the rotational speed in revolutions per minute (rev min1), P is
the power developed (kW), and H is the effective head (m).

34. The speed factor
The speed factor, , is the ratio of the peripheral speed, , of the buckets
or vanes at the nominal diameter, D, to the theoretical velocity of water
under the effective head, H, acting on the turbine:
/(2gH)1/2 DN/(84.6H1/2).

36. Components of hydropower plants
The various appurtenances connecting the construction and operation of
hydroelectric power plants are as follows: dams (storage or diversion type
control works); gates; valves; intakes; waterways (open channel or lowpressure
tunnel head race); high-pressure pipes (penstocks); fish passes

37. Head race
The head race is a conveyance for water from the source (reservoir or
river) to the power plant in the form of a canal (open waterway), tunnel
(low-pressure conveyance) or penstock (high-pressure conveyance) . The
open waterway usually terminates in a forebay which is an enlarged body
of water from which the penstocks convey the water to the turbines in the
power house.

38. Types of hydraulic turbines
ImpulsTurbines
All of the available potential energy (head) of the water is converted
into kinetic energy with the help of a contracting nozzle (flow rate
controlled by spear-type valve provided at the delivery end of the
pipeline (penstock). After impinging on the curved buckets the water
discharges freely (at atmospheric pressure) into the downstream
channel (called the tail race). The most commonly used impulse
turbine is the Pelt Large units may have two or more jets impinging at
different locations around the wheel.

39. Reaction Turbines
only a part of the available energy of the water is converted into kinetic
energy at the entrance to the runner, and a substantial part remains in the
form of pressure energy

40. Generators
The generator is an electrical machine coupled to the turbine shaft (either
horizontally or vertically). The alternating current (a.c.) synchronous generator is
widely used in hydroelectric power production practice. It has two elements, a
magnetic field consisting of an assembly of electromagnets (poles) which rotates
(hence rotor), within a stator (stationary unit) which is a system of conductors
(armature windings). The relative displacement between the rotor and the stator
induces an alternating electromotive force

41. Transformers
The transformers connecting the power source (generators) and the
receiving circuit (transmission lines) step up the voltage for transmission,
thus reducing the power loss and permitting the use of smaller conductors
(cables) in the transmission line. The transformers are usually located in
outside switchyards adjacent to the power house, as a necessary
precaution to avoid high voltage and other hazards.

42. Power house
The power house structure can be divided in two sections, a
substructure supporting the hydraulic and electrical equipment and a
superstructure housing the equipment. The substructure is usually a
concrete block with all the necessary waterways formed within it. The
scroll case and draft tube are usually cast integrally (especially in large
low-head plants) with the substructure with steel linings.
The superstructure usually houses the generating units and exciters, the switch
board and operating room

43. Tail race
The tail race is the waterway into which the water from the turbine units is
discharged (through draft tubes if reaction-type units are used). It may be very
short and if the power house is close to the stream the outflow may be
discharged directly into it. On the other hand, if the power house is situated at
a distance from the stream the tail race may be of considerable length. Proper
tail race design ensures, especially in low-head plants, that more of the plant
gross head is available for power development.

44. Surge tanks
Their primary purpose is the protection of the long pressure tunnel in
medium- and high-head plants against high waterhammer pressures
caused by sudden rejection or acceptance of load. The surge tank
converts these fast (waterhammer) pressure oscillations into much
slower – and lower – pressure fluctuations due to mass oscillation in
the surge chamber

45. Importance of Hydropower
 Hydropower is a renewable source of energy
Hydropower uses the energy of flowing water, without depleting it,
to produce electricity; therefore, all hydropower projects – small or
large, run-of-river or storage –meet the definition of renewable.
 Hydropower supports the development of other
renewable energies
Hydropower facilities with reservoirs offer unique operational flexibility in that they can
respond immediately to fluctuating demand for electricity. Hydropower’s flexibility and
storage capacity make it the most efficient and cost-effective way to support the
deployment of intermittent renewables such as wind or solar power
Reference:

46.  Hydropower fosters energy security and price stability
River water is a domestic resource and, unlike fuel or natural gas, it is
not subject to market fluctuations; moreover, hydropower is the only
major renewable source of electricity, and its cost-effectiveness,
efficiency, flexibility and reliability help optimize the operation of
thermal plants.
 Hydropower can reduce pollution
Hydropower plants produce no air pollutants. Very often, they replace
fossil-fuelled generation, thereby reducing acid rain and smog. Moreover,
hydropower projects do not generate any toxic by-products

47.  Hydropower improves electricity grid stability and
reliability
The management of electricity grids depends upon fast, flexible
generation sources to meet peak power demands, maintain level
system voltages and quickly restore service after a blackout. Electricity
generated from hydropower can be placed on the grid faster than any
other energy source. Hydropower’s ability to go from zero power to
maximum output rapidly and predictably makes it exceptionally good at
meeting changing loads and providing ancillary electrical services that
maintain the balance between electricity supply and demand.

48.  Hydropower helps fight climate change
The life cycle of hydropower produces very small amounts of
greenhouse gases (GHGs). By offsetting GHG emissions from gas, coal
and oil fired power plants, hydropower can help slow global warming.
Although only 33% of potential hydro resources have been developed,
hydropower currently avoids burning 4.4 million barrels of oil-equivalent
daily, worldwide