ELEMENTS OF Hydraulic POWER PLANTS

D. KANAKARAJAASST. PROFESSOR

AITSTIRUPATI

Hydraulic Machines

Initially the water of the river is in Catchments Area. From catchments area the water flows to the dam. At the dam the water gets accumulated . Thus the

potential energy of the water increases due to the height of the dam .

When the gates of the dam are opened then the water moves with high Kinetic Energy into the penstock.

Through the penstock water goes to the turbine house.

Since the penstock makes water to flow from high altitude to low altitude, Thus the Kinetic Energy of the water is again raised.

In the turbine house the pressure of the water is controlled by the controlling valves as per the requirements.

The controlled pressurized water is fed to the turbine. Due to the pressure of the water the light weight turbine

rotates. Due to the high speed rotation of the turbine the shaft

connected between the turbine and the generator rotates . Due to the rotation of generator the ac current is

produced. This current is supplied to the powerhouse . From powerhouse it is supplied for the commercial

purposes.

No fuel charges. Less supervising staff is required. Maintenance & operation charges are very low. Running cost of the plant is low. The plant efficiency does not changes with age. It takes few minutes to run & synchronize the plant. No fuel transportation is required. No ash & flue gas problem & does not pollute the

atmosphere. These plants are used for flood control & irrigation

purpose. Long life in comparison with the Thermal & Nuclear

Power Plant.

The initial cost of the power plant is very high. Takes long time for construction of the dam. Generally, Such plant’s are located in hilly area’s far

away from load center & thus they require long transmission lines & losses in them will be more.

Power generation by hydro power plant is only dependant on natural phenomenon of rain .Therefore at the time of drought or summer session the Hydro Power Plant will not work.

PURPOSES OF MULTIPURPOSE HYDROPROJECT

For irrigation of agricultural land.For navigation.For fisheries and tourism.For flood control.For civil water supply.For generation of electricity.

Components of hydel schemeThe principal components are:

1. Forebay2. Intake structure3. Penstocks4. Surge tank5. Turbines6. Power house7. Draft tube8. Tail race

PRIMARY ELEMENT’S CATCHMENTS AREA RESERVOIR DAM PRIME MOVERS DRAFT TUBES POWER HOUSE & EQUIPMENTSAFETY DEVICE’S SPILL WAY’S SURGE TANK TRASH RACKintake house.

water way.Tail race or outlet water way.

BASIC ELEMENTS OF HYDEL POWER PLANT

• Reservoir• Dam• Trace rack• For bay• Surge tank• Penstock• Spillway• Turbine• Powerhouse

The whole area behind the clam training into a stream as river across which the dam has been built at suitable place is called catchments area

A reservoir is employed to store water which is further utilized to generate power by running the hydroelectric turbines.

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.

A dam is a barrier which confines or raise water for storage or diversion to create a hydraulic head.

Dam’s are generally made of concrete, Stone masory, Rockfill or Timber

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.

• Dam are classified based on following factors:a) Functionb) Shapec) Construction materiald) Designa) Based on function the dam may be called as storage dam, diversion dam or detention dam.b) 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.d) According to structural design the dam maybe classified as:i. Gravity damii. Arch damiii. Buttress dam

Types of Dam:1. Masonry Dams.2. Earth Dams.The masonry dams are of three major classes:a) Gravity dam.b) Buttress dam.c) Arched dam.

d) Gravity dam:Resist the pressure of water by its weight.Construction of material used for his dam, is solid masonry or concrete.

Types of Dam:1. Masonry Dams.2. Earth Dams.The masonry dams are of three major classes:a) Gravity dam.b) Buttress dam.c) Arched dam.

d) Gravity dam:Resist the pressure of water by its weight.Construction of material used for his dam, is solid masonry or concrete.

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

type of dam is selected.

Arch Dams

• Arch shape gives strength• Less material (cheaper)• Narrow sites• Need strong abutments

Arch DamMonticello Dam impounds Putah Creek west of Sacramento, California. The solid concrete structure stands 93 m (304 ft) tall. The dam’s arched upstream face transfers some of the pressure from its reservoir, Lake Berryessa, onto the walls of the canyon.

Multiple Arch DamBartlett Dam impounds the Verde River northeast of Phoenix, Arizona. Like all multiple arch dams, Bartlett Dam makes use of a series of arches supported by buttresses to withstand the pressure of the water in its reservoir, Bartlett Lake. Each of the dam’s 10 concrete arches has a 7-m (24-ft) radius and measures 2 m (7 ft) at the base and just 0.6 m (2 ft) at the crest. The thick base provides additional strength at the bottom of the reservoir, where the water pressure is most intense.

Concrete Gravity Dams

• Weight holds dam in place

• Lots of concrete (expensive)

Flat Slab Buttress DamLake Tahoe Dam impounds the Truckee River in northern California. Like all flat slab buttress dams, it has a flat slab upstream face supported by a series of buttresses on the downstream side. Lake Tahoe Dam measures 5.5 m (18 ft) tall and 33 m (109 ft) long. It was completed in 1913 to raise the water level in Lake Tahoe, a natural lake, to provide additional water for crop irrigation..

Buttress Dams

• Face is held up by a series of supports

• Flat or curved face

EARTH/ Embankment Dams

• Earth or rock• Weight resists flow of

water

Intake structure• Water conveyed from forebay to

penstocks through intake structures.• Main components are trash rack and

gate.• Trash rack prevent entry of debris.

Water Ways.

1. 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.

2. 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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Spillway

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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.

• Modern dams use (1) vertical lift gates, (2) traitor (radial)• gates, (3) wheeled gates, (a) roller gates, (b) drum or cylindrical• gates and (c) butterfly valves etc.

Pressure tunnel: It is a passage that carries water from the reservoir to the

surge tank.

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1. Crest control2. Crest gates3. Sluice gates and valves.

Surge tank • additional storage for near to turbine, usually

provided in high head plants.• located near the beginning of the penstock.• As the load on the turbine decreases or during load

rejection by the turbine the surge tank provides space for holding water.

Surge Shaft• Surge shaft is located at the end of tunnel . • It is a well type structure of suitable height

and diameter to absorb the upcoming and lowering surges in case of tripping and starting of the machine in the power house.

• The surge shaft is provided with gates to stop flow of water to the penstock if repairs are to be carried out in the penstock or inlet valves.

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 :o 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

40

• surge tank over comes the abnormal pressure 

in the conduit when load on the turbine falls and acts as a reservoir during increase of load

on the turbine.

Penstock• Penstocks are the water conductor conduit of suitable

size connecting the surge shaft to main inlet valve• It allows water to the turbine through main inlet valve.• At the end of the penstock a drainage valve is provided

which drains water from penstock to the draft tube.• In case of long penstock and high head, butterfly valve

is provided just before the penstock.• It takes off from the surge shaft in addition to spherical

valve at the end of the penstock acting as the main inlet valve.

Penstock thickness: • The thickness of penstock depend on water head and hoop

stress allowed in the material.t

Where,t= Penstock thicknessd= Dia of penstock= Permissible stressp= Pressure due to water including water hammer.

Number of penstockA 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.

Penstock Protection Valve

The Penstock protection valves are provided after the surge shaft to facilitate maintenance of the penstocks. The valves are of butterfly type. The BF valve are operated hydraulically with provision of pressure accumulators in case of power failure.

Forebay • Enlarged body of water provided in

front of penstock.• Provided in case of run off river plants

and storage plants.• Main function to store water which is

rejected by plant.• Power house located closed to dam

penstock directly take water from reservoir, reservoir act as forebay.

Water Intake Structure• It consists of gated structure at the

dam/Barrage to control the flow of water and provided with gates along with hoisting arrangement.

• Normally these gates remain open and allows water to flow to the tunnel /channel as the case may be until and unless water conductor system is taken under shut down for repair and maintenance.

Pressure Shaft

• When the water conduits in the Surge shaft and Main Inlet valve are not exposed to the atmosphere and buried in the ground/concrete due to its high pressure, these are called Pressure shaft.

Main Inlet Valve• Main inlet valve works as the gate

valve/isolating valve in the water conductor system.

• It is located before turbine and allows water flow from penstock to turbine.

• MIV acts as closing valve and cuts the flow of water during an emergency trip.

• They are of following type.• Butterfly valve (upto 200 m head)• Spherical valve (more than200m head)

BUTTERFLY VALVE

BUTTERFLY VALVE

SPHERICAL VALVE

Turbines

• turbines are used to convert the energy water of falling water into mechanical energy.

• water turbine is a rotary engine that takes energy from moving water. 

• flowing water is directed on to the blades of a turbine runner, creating a force on the blades.

• Since the runner is spinning, the force acts through a distance n this way, energy is transferred from the water flow to the turbine. 

• The principal types of turbines are:1)    Impulse turbine2)    Reaction Turbine

Kaplan

Francis

Draft tube• is a pipe or passage of gradually

increasing cross sectional area, which connect to the exit to tail race.

• it reduces high velocity of water discharged by the turbine.

• draft tube permits turbines to be installed at a higher level than the tail race level, which help the maintaince and repair of turbines.

Draft Tube• Draft tube is located between lower ring of turbine

and tail race . It conveys water after discharge from runner to tail race tunnel.

• Draft tube (DT) gates are provided for isolating the Power house and tail pool before taking maintenance of the turbine.

• The DT gates are provided with hoisting mechanism.

• The DT gate may be a single piece or a combination of more than one piece

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(1) 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%.

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.

Spill Way’s is a kind of canal provided besides the dam.

Spill Way’s is used to arrange the excess of accumulation of water on the dam because excess accumulation of water may damage the dam structure

1. Over flow spillway2. Chute or trough spillway3. Side channel spillway4. Shaft spillway5. Siphon spillway'.

The amount of electricity that can be generated by a hydropower plant depends on two factors:• flow rate - the quantity of water flowing in a given time; and• head - the height from which the water falls.The greater the flow and head, the more electricity produced.

Flow Rate = the quantity of water flowing Head = the height from which water falls

Power generation

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:i. Turbinesii. Generatorsiii. Governorsiv. Relief valve for penstock settingv. Gate valvevi. Transformervii. Switch board equipment and instrumentsviii. Oil circuit breakerix. Storage batteriesx. Outgoing connectionsxi. Cranesxii. Shops & offices

The surface power house has been broadly divided into three subdivisions which is separatedfrom the intake as mentioned below :(a) Substructure ;(b) Intermediate structure ;

(c) Super-structure.

Tail water level or Tail race:o 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.

GENERATOR

• Hydro generator is coupled to the turbine and converts the mechanical energy transmitted by the turbine to electrical energy• Generators can be of:

• Suspended type • Umbrella type

• Main Generator components include:• Stator• Rotor• Upper Bracket • Lower Bracket• Thrust Bearing & Guide Bearings• Slip Ring & Brush Assembly• Air Coolers• Brakes & Jacks• Stator Heaters

GOVERNOR

• Used for controlling the guide vanes by detecting turbine speed & its guide vane opening in order to keep turbine speed stable or to regulate its output.

• The performance of the governor dominates the controllability of the power plant and quality of electrical power produced .

AUXILIARIES ATTACHED WITH HYDEL POWER PLANT.

(A)Electrical instruments

• Generator• Exciter,transformers• Switch gears• Other instruments of

control room

(B)Mechanical instruments

• Shaft coupling,journal bearings,thrust bearings

• Lubricating oil system• Cooling system• Brake system for

generator-turbine shaft

Because water delivery is the first priority, electricity produced at Arizona Falls is used mainly to supplement high electricity demands in the summer.

Hydropower is an important renewable energy source world wide...

we can experience new, renewable technologies with the power of water!

Even here in our desert home,

Advantages of hydropowerIt is a clean and safe source of energyThey are self sustainingThey create habitat for more types of fishThey can act as a flood controllerThey are the most efficient energy source running from 90-95% efficiency

Other forms of HydropowerTidal power: electricity generated by turbines moved by the tides. This is still in experimental stages.Ocean thermal power: power generated by the thermal expansion of the ocean. This can only be used in a location like the Gulf stream.Geothermal power: natural steam is used underground to turn turbines. This is limited to location which have these phenomenon.

Advantages of hydropowerIt is a clean and safe source of energyThey are self sustainingThey create habitat for more types of fishThey can act as a flood controllerThey are the most efficient energy source running from 90-95% efficiency

1 Itaipu Brazil/Paraguay

12,600 1984

2 Guri Venezuela 10,300 19683 Grand Coulee United

States6,480 1942

4 Sayano-Shushensk

Russia 6,400 1980

5 Krasnoyarsk Russia 6,000 19686 La Grande 2 Canada 5,328 19827 Churchill Falls Canada 5,225 19718 Bratsk Russia 4,500 19649 Ust-Ilim Russia 4,500 1974

10 Tucurui Brazil 4,245 1984

Rank Name of Dam Location

Rated Capacity (Megawatts)

Year of Completed

World’s Largest DamsBy Power Generating Capacity

1 Owen Falls Uganda 204,800 19542 Kariba Zimbabwe

/Zambia180,600 1959

3 Bratsk Russia 169,270 19644 Aswan High Egypt 168,900 19705 Akosombo Ghana 148,000 19656 Daniel Johnson Canada 141,852 19687 Guri

(RaulLeoni)Venezuela 136,000 1986

8 Krasnoyarsk Russia 73,300 19679 W.A.C. Bennett Canada 70,309 196710 Zeya Russia 68,400 1978

Rank Name of Dam Country

Storage Capacity Cubic Meters

Year of Completed

World’s Largest DamsBy Storage Capacity

1 Rogun Tajikistan 335 19892 Nurek Tajikistan 300 19803 Grand Dixence Switzerland 285 19614 Inguri Georgia 272 19805 Boruca Costa Rica 267 19906 Vaiont Italy 262 19617 Chicoasen Mexico 261 19808 Manuel M.

TorresMexico 261 1981

9 Alvaro Obregon

Mexico 260 1946

10 Mauvoisin Switzerland 250 1957

Rank Name of Dam CountryHeight (m)

Year of Completed

World’s Largest DamsBy Height