Hydro Electricity 29-01-13 Fn

7/28/2019 Hydro Electricity 29-01-13 Fn

1/87

6/15/2013 M L SHESHADRI 1

HYDRO ELECTRICITY

The Three Gorges Dam is the largest operating hydroelectric power station, at 22,500 MW.


2/87


HYDRO ELECTRICITY

Hydro power, hydraulic power, hydro electric power orwater power is the power that is derived from the forceor energy of falling or flowing water which may be

harnessed for useful purposes.

Since ancient times, hydro power has been used forirrigation and the operation of various mechanical

devices, such as watermills, sawmills, textile mills, dockcranes and domestic lifts.


3/87


HYDRO ELECTRICITY

Since the early 20th century, the term hydro electricity isused almost exclusively in conjunction with the modern

development of hydro electric power, the energy ofwhich could be transmitted considerable distancebetween where it was produced to where it isconsumed.

There are several mature forms of water power in wideusage currently. Most hydro power is used primarily togenerate electricity.


4/87


HYDRO ELECTRICITY

Another previous method used to transmit energy hademployed atrompe, which produces compressed airfrom falling water, that could then be piped to othermachinery at a distance from the energy source.

Waters power is manifested in hydrology, by the forceof water on the river bed and banks of river. When ariver is in flood, it is at its most powerful, and moves thegreatest amount ofsediment. This higher force results in

the removal of sediment and other material from theriver bed and banks of the river, locally causing erosion,transport and, with lower flow, sedimentationdownstream.


5/87


HYDRO ELECTRICITY

Hydro electricity is the term which refers to electricitygenerated by hydro power; the production of electricalpower through the use ofgravitational force of falling orflowing water.

It is the most widely used form ofrenewable energy.

Compared to other sources of energy hydro electricity ismore environment friendly.

World wide, an installed capacity of 1010 GW suppliedhydro electricity in 2010.

Hydro electricity account for 21% of renewable sources.


6/87


HYDRO ELECTRICITY

History of hydro electricity development

1878worlds first hydro electric scheme at Cragside,England.

1881 Schoelkopf power station-1 near Niagara Falls inthe U.S. side

1882 Edison hydro electric plant at Appleton with anoutput of 12.5 kilowatts

1889 there were 200 hydro electric stations in the U.S.

At the beginning of the 20th century, many small hydroelectric power plants were constructed by commercialcompanies in mountains near metropolitan areas.


7/87


HYDRO ELECTRICITY

After the administration introduced regulations for hydro electricitydevelopment, large dams were built to meet the irrigation and floodcontrol needs.

Hoover dam 1928 and Bonneville Dam 1937 are examples.

Hoover Dam 1345 MW was the largest in 1936;Grand coulee Dam 6809MW eclipsed it in 1942;Itaipu Dam in South America with 14000 MW was the largest in1984;The Three Gorges Dam in China with 22,500 MW surpassed all thesein 2008

Countries like Norway, Congo, Paraguay and Brazil are meeting theirelectricity needs with 85% hydro electricity.


8/87


HYDRO ELECTRICITY

Generating methods of hydro electricity

Conventional hydro electric schemes by building damacross the river.

Under ground hydro electric scheme

Pumped storage scheme

Run of the river scheme

Tidal power plant

Compressed air from water falling in a column


9/87


HYDRO ELECTRICITY

Conventional hydro electric schemes bybuilding dam across the river.

The potential energy of water held in the reservoirformed due to construction of dam is utilized to drive awater turbine which is coupled to the generator toproduce electricity. The water from the reservoir is led to

the turbine using heavy pipes called penstock. Thepower potential is dependent on the difference in heightof water in the reservoir and the tail water outlet of theturbine called head.


10/87


The Ffestiniog Power Station can generate 360 MW of electricity within 60

seconds of the demand arising.


11/87


The Bhakra Dam 1325 MW


12/87


The Narmada Dam 1450 MW


13/87


The Srisailam Dam 1670 MW


14/87


The Hoover Dam in the United States is a large conventional dammed-

hydro facility, with an installed capacity of 2,080 MW.


15/87


The Grand Coulee Dam 6809 MW


16/87


The Itaipu Dam 14,000 MW


17/87


Turbine row at Los Nihuiles Power Station in Mendoza, Argentina


18/87


HYDRO ELECTRICITY

Under ground hydro electric scheme

An underground power station makes use of a largenatural height difference between two waterways, suchas a waterfall or mountain lake. An underground tunnelis constructed to take water from the high reservoir tothe generating hall built in an underground cavern nearthe lowest point of the water tunnel and a horizontaltailrace taking water away to the lower outlet waterway.

HYDRO ELECTRICITY


19/87


HYDRO ELECTRICITY HYDRO ELECTRIC POWER GENERATION

underground power house


20/87


HYDRO ELECTRICITY Pumped storage scheme

This method produces electricity to supply high peak demands by

moving water between reservoirs at different elevations.

At times of low electrical demand, excess generation capacity isused to pump water into the higher reservoir.

When there is higher demand, water is released back into the lowerreservoir through the turbine.

Pumped storage schemes currently provide the most commerciallyimportant means of large scale grid energy storage and improve thedaily capacity factor of the generating system.

Run of the river schemeRun of the river hydroelectric stations are those with small or noreservoir capacity, so that the water coming from upstream must beused for generation at that moment, or must be allowed to by passthe facility.

V ti l K l T bi ( t VERBUND A t i H d P )


21/87


Vertical Kaplan Turbine (courtesy VERBUND-Austrian Hydro Power)

Tyson turbines (fixed propeller)


22/87


Horizontal Bulb turbine. (courtesy VERBUND-Austrian Hydro Power).


23/87


A micro-hydro facility in Vietnam


24/87


Pico hydroelectricity in Mondulkiri, Cambodia

HYDRO ELECTRICITY


25/87


HYDRO ELECTRICITYTidal power plant

Tidal power is extracted from the Earths oceanic tides; tidal forcesare periodic variations in gravitational attraction exerted by celestialbodies.

It is a renewable source and most predictable as compared to solarand wind energy.

Tidal stream generators make use of the kinetic energy of movingwater to power turbines, in a similar way to wind turbines.

Tidal barrage make use of potential energy of the head betweenhigh and low tides.

Dynamic tidal power exploits the interaction between potential andkinetic energies in tidal flows.

Research in this area is going on.

HYDRO ELECTRICITY


26/87


HYDRO ELECTRICITY

Compressed air from water falling in a column

A falling column of water is purposely mixed with air bubblesgenerated through turbulence at the high level intake.

This is allowed to fall down a shaft into a subterranean high roofedchamber where the compressed air gets separated from water and

becomes trapped.

The height of the falling water column maintains the air pressurewhile an outlet submerged below the water level in the chamberallows water to flow back to the surface at a slightly lower level

than the intake.

A separate outlet in the roof of the chamber supplies thecompressed air to the surface.


27/87


HYDRO ELECTRICITY Sizes and capacities of hydro electric facilities Large : 500 MW to more than 10 GW

(large hydroelectric projects supply public electricity network. The threegorges dam is the largest operating hydroelectric station at 22,500 MW)

Medium : 10 MW to 500 MW(medium hydroelectric projects serve a large community through a regional

grid or industrial plant)

Small : up to 10 MW(small hydroelectric projects serve a small community or industrial plant)

Micro : up to 100 KW(serves small isolated communities and complements solar photovoltaic

energy especially in winter where solar energy is minimum)

Pico : up to 5 KW(serves small remote communities that require only a small amount ofelectricity to power light, TV, Radio etc,.)


28/87


HYDRO ELECTRICITY

Advantages

Elimination of cost of fuel.

Long economic life (50 to 100 years).

Dam can be constructed for multiple purposes to provide a usefulrevenue stream to offset the cost of dam operation.

Irrigation , aquaculture, water sport and tourism are possible withmulti purpose hydro electric projects.

Since hydro electric projects do not burn fossil fuels, they do notdirectly produce carbon dioxide.

HYDRO ELECTRICITY


29/87


HYDRO ELECTRICITY Disadvantages

Large reservoirs submerge vast areas upstream of the damdestroying biologically rich and productive low land, river valleyforests, marsh land and grass lands.

Silt can fill the reservoir and reduce its capacity to control floods.

Climate change affect amount of river flow and power out put isaffected.

The reservoirs may produce substantial amount of methane a greenhouse gas due to plant material in flooded areas decaying in ananaerobic environment.

Need to relocate people living where the reservoir is planned whichresults in fragmentation of habitat and life style destruction.

Dam failure either due to poor construction or terrorist acts can becatastrophic.

HYDRO ELECTRICITY


30/87


HYDRO ELECTRICITY Disadvantages (large area submerged)


31/87


HYDRO ELECTRICITY

Hydro electric -capacity factor

A hydro electric plant rarely operates at its full powerrating over a full year, the ratio between annual average

power and installed capacity rating is the capacity factor.

Paraguay produces 100% of its electricity from hydroelectric dams, and exports 90% of its production toBrazil and Argentina.

Norway produces 98.99% of its electricity from hydroelectric sources.


32/87



33/87


HYDRO ELECTRICITY

India (hydro electricity produced in 2009)

Annual energy produced 115.6 TWh

Installed capacity 33.6 GW

Capacity factor 0.43 % of total capacity 15.8


34/87


HYDRO ELECTRICITY

Hydro electric power development investigations:

The economic soundness of a hydro electric projectdepends mainly on firm power that which can be

maintained during the most critical rainfall conditions.

To estimate the power potential and economic viabilitythe following are to be investigated;

1. Hydrological data for at least last 50 years2. Topographical investigations of dam sites, reservoirs,

water conductor systems, power house sites etc,.3. Geological investigations.

HYDRO ELECTRICITY


35/87


HYDRO ELECTRICITY investigations:

Estimation of power potential;

A hydro power resource can be measured according tothe amount of available power, or energy per unit time.

In large reservoirs the available power is a function ofthe hydraulic head and rate of fluid flow.

In a reservoir the head is the height of water in thereservoir relative to its height after discharge.

Each unit of water can do an amount of work equal toits weight times the head.


36/87


HYDRO ELECTRICITYThe amount of energy E released when an object of mass m drops a

height h in a gravitational field of strength g is given by

E = m g hThe energy available to hydro electric dams is the energy that canbe liberated by lowering water in a controlled way. In thesesituations, the power is related to the mass flow rate.

E/t = (m/t) g hSubstituting P for E/t and expressing m/t in terms of the volume of

liquid moved per unit time (the rate of fluid flow ) and the densityof water, we obtain the usual form of this expressionP = g h

ORA simple formula for approximating electric power production at hydro

electric plant is:

P = h r g kWhere P is power in KW, h is height in meter, r is flow rate in cubic

meter per second, g is acceleration due to gravity and kis acoefficient of efficiency.

The combined efficiency of turbine and generator is usually 85%


37/87


HYDRO ELECTRICITY

Some hydro power systems such as water wheels candraw power from the flow of a body of water withoutnecessarily changing its height. In this case, theavailable power is the kinetic energy of flowing water.

P = v2

where v is the speed of the water.

Substituting, = A v, Ais the area through which waterpasses

P =1/2 v3

Over shot water wheels can efficiently capture both typesof energy.


38/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWER GENERATION

A hydro electric power plant converts the inherent energy of waterunder pressure into electric energy.

The size, location, and type of power plant depend upon thetopography, the geological conditions, and the amount of water andhead available.

Hydro power developments can be classified as low-head, medium-head, or high-head.

Outline of the most common arrangements and features of hydroelectric developments are shown in the next slide.

HYDRO ELECTRICITY


39/87




40/87


Cross section of a conventional hydroelectric dam.

HYDRO ELECTRICITY


41/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWER GENERATION Main elements of the hydro generation scheme

An upper or high levelReservoir, usually formed by building a damacross a river.

AnIntake, consisting of a canal or concrete passageway to carrythe water in a controlled way directly to low head turbines or to the

pressure conduit used for medium and high head turbines.

APressure conduit, consisting of a tunnel, pipeline, or penstock,or any combination thereof, to carry the water under pressure tomedium and high head turbines.

ASurge tank, to prevent excessive pressure rises and drops duringsudden load changes, installed somewhere along the pressureconduit when this conduit is quite long.

HYDRO ELECTRICITY


42/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWER GENERATION Main elements of the hydro generation scheme

Trash racks at the inlet to the Intake or pressure conduit. They areprovided to protect the turbine against floating or other material.Cleaning devices such as rakes, either manual or motor operated,

are provided to remove debris from the racks.

Head gates or stop logs are provided at the inlet to the intake orconduit and at the outlet of the draft tube for shutting off the flowto the turbine for safety and ease of maintenance. These gates arelowered or raised by a motor operated crane.

ADraft tube, usually a part of the power house structure to carrythe water away from the turbine runner.

HYDRO ELECTRICITY


43/87


HYDRO ELECTRICITY HYDRO ELECTRIC POWER GENERATION Main elements of the hydro generation scheme

Penstocks are the closed conduits connecting the upper reservoir,tunnel, or surge tank with the turbine casing. In medium headinstallations, each turbine usually has its own penstock. In the caseof high heads, a single penstock is frequently used and branch

connections provided at the lower end to supply two or moreturbines.

Penstock valves located at the intake to the turbine spiral caseare usually provided when the conduit is of considerable length.This permits shutting off the flow to each turbine, for safety andmaintenance and to reduce leakage losses during long turbineshutdowns, without having to drain and refill a long conduit.

Penstock valvesare also a necessity where more than one turbine isconnected to a single conduit so that flow can be shut off to eachturbine individually.

HYDRO ELECTRICITY


44/87



Butterfly valvesare most commonly used as turbine inlet valvesfor low and medium head turbines. Due to excessive loss inbutterfly valves, spherical valves are used in high head turbines.

AHydraulic Turbine consisting primarily of a runner, connected toa shaft, for producing prime motive power from the inherent energyof the water under pressure, a mechanism for controlling thequantity of water flowing to the runner, and water passages leadingto and away from the runner.

AGovernorfor operating the hydraulic turbine control mechanism.

An Electric Generator connected to the hydraulic turbine shaft toconvert the prime motive power of the turbine to electric power.

HYDRO ELECTRICITY


45/87



APressure regulator, some times used instead of a surge tank, toprevent excessive pressure rises and drops during sudden loadchanges in plants with long pressure conduits.

APower House to enclose and support the hydraulic turbine,generator, governor, pressure regulator (if used), and auxiliaries.

ATail race, sometimes used to carry the water away from the drafttube to the tail race reservoir.

ATail water reservoir which receives the water discharged fromthe draft tube or tail race and is usually part of the original river atan elevation lower than the upper reservoir.

HYDRO ELECTRICITY


46/87


HYDRO ELECTRICITY HYDRO ELECTRIC

POWER GENERATION

Water turbine

Water wheels have beenused for thousands of yearsfor industrial power. Theirmain shortcoming is size,which limits the flow rateand head that can beharnessed.

The migration from waterwheels to modern turbinestook about one hundredyears during industrialrevolution.

HYDRO ELECTRICITY


47/87


HYDRO ELECTRICITY HYDRO ELECTRIC POWER GENERATION Water turbine

The word Turbine was introduced by the French engineerClaude Bourdin in the early 19th century and is derivedfrom the Latin word for whirling or a vortex.

The main difference between early water turbines andwater wheels is a swirl component of the water whichpasses energy to a spinning rotor.

This additional component of motion allowed the turbineto be smaller than a water wheel of the same power.

They could process more water by spinning faster andcould harness much greater heads.

Later, impulse turbines were developed which did not useswirl.

HYDRO ELECTRICITY


48/87


HYDRO ELECTRICITY HYDRO ELECTRIC POWER

GENERATION

Water turbine

A water turbine is a rotaryengine that takes energy

from moving water.

Developed in 19th centuryfor industrial power prior to

electrical grids.

Now it is mostly used forelectric power generation.


49/87


HYDRO ELECTRICITY

HYDRO ELECTRICPOWER GENERATION

Water turbine

The runner of the smallwater turbine

Various types of water turbine runners. From left to right: Pelton Wheel, two


50/87


types of Francis Turbine and Kaplan Turbine

HYDRO ELECTRICITY


51/87


HYDRO ELECTRICITY

HYDRO ELECTRICPOWER GENERATION

Water turbine (theory ofoperation)

Newtons third lawdescribes the transfer of

energy for reactionturbines.

Most water turbines inuse are reaction turbinesand are used inlow(


52/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWERGENERATIONWater turbine (types)

Reaction turbines:FrancisKaplan (fixed blade, adjustable

blade, propeller)

Impulse turbines:Water wheelPeltoncross flow


53/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWER GENERATION Water turbine (theory of operation)

Flowing water is directed on to the blades of a turbinerunner, creating a force on the blades.

Since the runner is spinning, the force acts through adistance (force acting through a distance is the definition ofwork). In this way, energy is transferred from the waterflow to the turbine.

Water turbines are divided into two groups; reactionturbines and impulse turbines.

The precise shape of water turbine blades is a function ofthe supply pressure of water, and the type of impellerselected

HYDRO ELECTRICITY


54/87


HYDRO ELECTRICITY HYDRO ELECTRIC POWER GENERATION Water turbine (theory of operation)

Reaction turbines are acted on by water, which changespressure as it moves through the turbine and gives up itsenergy.

They must be encased to contain the water pressure or theymust be fully submerged in the water flow.

Inward flow water turbines have a better mechanicalarrangement and all modern reaction water turbines are ofthis design. As the water swirls inward, it accelerates, andtransfers energy to the runner. Water pressure decreases to

atmospheric, or in some cases sub atmospheric, as thewater passes through the turbine blades and loose energy.

Kaplan turbine, a propeller type machine was an evolutionof the Francis turbine but revolutionized the ability todevelop low head hydro sites.

HYDRO ELECTRICITY


55/87


HYDRO ELECTRICITY HYDRO ELECTRIC POWER GENERATION Water turbine (theory of operation)-Impulse turbines

Impulse turbines change the velocity of a water jet. The jet pushes onthe turbines curved blades which changes the direction of the flow.

The resulting change in momentum (impulse) causes a force on the turbineblades.

Since the turbine is spinning, the force acts through a distance (work) andthe diverted water flow is left with diminished energy.

Prior to hitting the turbine blades, the waters pressure (potential energy) isconverted to kinetic energy by a nozzle and focused on the turbine.

No pressure change occurs at the turbine blades, and the turbine does notrequire a housing for operation.

Newtons second law describes the transfer of energy for impulse turbines

The impulse turbines are most often used in very high (>300 m) headapplication.

Assembly of a Pelton wheel at Walchensee Power Plant


56/87


Assembly of a Pelton wheel at Walchensee Power Plant

Plan view of a Pelton turbine installation.


57/87


HYDRO ELECTRICITY


58/87


HYDRO ELECTRICITY


Water turbine

Francis turbine

Francis turbine is a type of water turbinedeveloped by James B Francis in Lowell,Massachusetts.

It is an inward flow reaction turbine thatcombines radial and axial flow concepts.

HYDRO ELECTRICITY


59/87


HYDRO ELECTRICITY


Water turbineFrancis turbine

Francis turbines are the most common water turbine in use today.

They operate in a range of 10-650 meter head and are primarilyused for electric power production

The power output generally ranges from 10-750 MW

Runner diameter are between 1-10 meter and the speed range ofthe turbine will be in the range of 80-1000 rpm.

Large turbines are arranged with a vertical shaft and only very lowsized turbines are arranged with horizontal shaft.

HYDRO ELECTRICITY


60/87



Water turbineFrancis turbine (theory of operation)

The Francis turbine is a reaction turbine, which means that the workingfluid changes pressure as it moves through the turbine, giving up itsenergy.

A casement is needed to contain the water flow. The turbine is located

between the high pressure water source and the low pressure waterexit, usually at the base of the dam.

The inlet is spiral shaped. Guide vanes direct the water tangentially tothe turbine wheel, known as the runner. This radial flow acts on therunner vanes, causing the runner to spin.

The guide vanes or (wicket gate) may be adjusted to allow efficientturbine operation for a range of water flow conditions.

HYDRO ELECTRICITY


61/87



Water turbine

Francis turbine (theory of operation)

As the water moves through the runner, its spinning radiusdecreases, further acting on the runner. Due to law of conservation

of angular momentum this property in addition to the waterspressure helps Francis and other inward flow turbines harness waterenergy efficiently.

At the exit water acts on the cup shaped runner features, leaving

with no swirl and very little kinetic or potential energy. The turbinesexit tube is so shaped to help decelerate the water flow and recoverthe pressure.

Three Gorges Dam Francis turbine runner


62/87


Francis Inlet Scroll, Grand Coulee Dam


63/87


,

A Francis turbine runner, rated at nearly one million hp (750 MW), being


64/87


installed at the Grand Coulee Dam, United States

A Francis turbine at the end of its life showing cavitations pitting, fatigue cracking and a


65/87


catastrophic failure. Earlier repair jobs that used stainless steel weld rods are visible.

HYDRO ELECTRICITY


66/87


HYDRO ELECTRIC POWER GENERATIONWater turbine

Kaplan turbine

The Kaplan turbine is a propeller type water turbine which has adjustable blades. Itwas developed in 1913 by the Austrian professor Viktor Kaplan, who combinedautomatically adjusted propeller blades with automatically adjusted wicket gates toachieve efficiency over a wide range of flow and water level.

The Kaplan turbine was an evolution of the Francis turbine. Its invention allowedefficient power production in low head applications that was not possible withFrancis turbines.

The head ranges from 10-70 meters and output from 5-120 MW.

The speed ranges from80-430 rpm.

Kaplan turbines are now widely used throughout the world in high flow, low headpower production.

HYDRO ELECTRICITY


67/87


HYDRO ELECTRIC POWER GENERATIONWater turbine

Kaplan turbine (theory of operation)

The Kaplan turbine is an inward flow reaction turbine, which means that theworking fluid changes pressure as it moves through the turbine and givesup its energy.

Power is recovered from both the hydrostatic head and from the kineticenergy of the flowing water.

The design combines features of radial and axial turbines.

The inlet is a scroll shaped tube that wraps around the turbines wicketgate. Water is directed tangentially through the wicket gate and spirals on

to a propeller shaped runner, causing it to spin.

The outlet is a specially shaped draft tube that helps decelerate the waterand recover kinetic energy.

HYDRO ELECTRICITY


68/87



Water turbine

Kaplan turbine (theory of operation)

The turbine need not be at the lowest point of water flow as long asthe draft tube remains full of water. A high turbine location,however, increases the suction that is imparted on the turbineblades by the draft tube. The resulting pressure drop may lead to

cavitations.

Variable geometry of the wicket gate and turbine blades allow efficientoperation for a range of flow conditions. Kaplan turbine efficienciesare typically over 90%, but may be lower in very low headapplications.

Because the propeller blades are rotated by high pressure hydraulic oil,a critical element of Kaplan turbine design is to maintain a positiveseal to prevent emission of oil into the waterway. Discharge of oilinto the river is not permitted.

A propeller-type runner rated 28,000 hp (21 MW)


69/87


A propeller type runner rated 28,000 hp (21 MW)

Vertical Kaplan Turbine (courtesy Voith-Siemens).


70/87


A Bonneville Dam Kaplan turbine after 61 years of service


71/87


HYDRO ELECTRICITY


72/87


HYDRO ELECTRICITYHYDRO ELECTRIC POWER GENERATIONWater turbines Pelton wheel

Theory of operation

The Pelton wheel is an impulse turbine which is among the most efficienttypes of water turbines.

It was invented by Lester Allan Pelton in the 1870s.

The Pelton wheel extracts energy from the impulse (momentum) of movingwater, as opposed to its weight like traditional overshot water wheel.

Earlier impulse turbines were less efficient and the design by Pelton withpaddle geometry yielded the speed of the rim of the runner as half the

speed of water jet, the water leaves the wheel with little speed, extractingalmost all of its energy, and thus a very efficient turbine.

Figure from Pelton's original patent (October 1880)


73/87


HYDRO ELECTRICITY


74/87


HYDRO ELECTRIC POWER GENERATIONWater turbines Pelton wheel

The water flows along the tangent to the path of the runner. Nozzles directforceful streams of water against a series of buckets mounted around theedge of a wheel.

As water flows into the bucket, the direction of the water velocity changes to

follow the contour of the bucket. When water jet contacts the bucket, thewater exerts pressure on the bucket and the water is decelerated as it doesa U-Turn and flows out at low velocity.

In the process, the water momentum is transferred to the turbine. ThisImpulse does work on the turbine.

As water is incompressible, all the energy is extracted in the impulse and henceonly one turbine stage is there in hydraulic turbine.

Old Pelton wheel from Walchensee Power Plant, Germany


75/87


HYDRO ELECTRICITY


76/87


HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects The laws of proportionality The variation of power, speed, and discharge with runner size and

head for turbines of varying size, but with the same basicdimensional relationship in water passageway design (also calledhomologous turbines) are shown in the following table.

HYDRO ELECTRICITY


77/87


HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects The following table is based upon general practice and is not to be

considered as limits for head for each type.

HYDRO ELECTRICITY


78/87


HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects


79/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects Specific speed (Ns) Specific speed is the common basis of comparison

between turbine runners of different types and between

runners of the same type but different design andperformance characteristics.

It is the constant relationship between the speed of arunner at the point of highest efficiency and themaximum power output at this speed, regardless of size.

It is the speed in revolutions per minute which therunner would have if operated under 1-ft head, therunner being of such size as to develop 1 hp.

Ns= nP/H5/4 for any size and type of runner operatingat speed n, with a power output of P under head H

HYDRO ELECTRICITY


80/87


HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects Specific speed (Ns)

The speed of the turbine should be as high as practical, as thehigher the speed, the smaller the overall size of the turbine andless costly. Also, since hydraulic turbines are usually connected toelectric generators, the higher the speed, the less costly and moreefficient are the generators.

The speed of the turbine is tied in with the specific speed Ns whichis a characteristic of each design of turbine runner, which in turnvaries with the head under which it will be used.

Since hydraulic turbines are usually directly connected toalternating current generators, the turbine speed must agree with

one of the nearest synchronous speeds as determined from thesystem frequency.

HYDRO ELECTRICITY



81/87


HYDRO ELECTRIC POWER GENERATIONWater turbines Pelton wheel

The specific speed of impulse units can be increased by increasing the number of jetsused on a single runner or by increasing the number of runners per unit.

HYDRO ELECTRICITY


82/87


HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects

Runaway speed If a reaction type turbine runner is allowed to revolve freely without load

and with the wicket gates wide open, it will over speed to a value calledrunaway speed. The runaway speed of a turbine at normal head varies withthe specific speed.

For Francis turbines the runaway speed varies from 155-195% of normalspeed for specific speed of 20-100

The runaway speed for impulse turbines ranges from 180-190% of normalspeed, depending upon the specific speed of the runner per jet. The higherthe specific speed, the higher is the runaway speed.

For all turbines, the maximum head is normally higher than the rated head.Therefore the runaway speed will be increased in proportion to the squareroot of the head. For this reason, runaway speeds should be based on themaximum operating head rather than on the rated head.


83/87


HYDRO ELECTRICITY

HYDRO ELECTRIC POWER GENERATION Water turbine Design Aspects Reaction turbine elements Thrust bearing

Runner and wearing rings Main shaft and bearing Spiral case Draft tubes Stay ring Wicket gates and operating mechanism

HYDRO ELECTRICITY


84/87


HYDRO ELECTRICITY Water turbine Design Aspects Impulse turbine elements

The runner

The nozzle pipe

The needle

The jet deflector

The housing

HYDRO ELECTRICITY


85/87


Water turbine Design Aspects Speed control

Speed control of a hydraulic turbine is provided byvarying the flow of water through the turbine.

This flow control is accomplished by changing theposition of wicket gates in the case of a reaction turbineand by needle stroke/ or the deflector position in thecase of an impulse turbine.

The turbine wicket gates, needles, or deflectors arepositioned by hydraulic servomotors which are controlledby the speed governor in response to changes in unitspeed or governor speed setting.

HYDRO ELECTRICITY


86/87


Water turbine Design Aspects Speed control

WATER POWER HARNESSED TO OBTAIN ELECTRIC POWER


87/87

WATER POWER HARNESSED TO OBTAIN ELECTRIC POWER

THANK YOU

Documents

Hydro Electricity 29-01-13 Fn