2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, EPOKA University, Tirana,

ALBANIA.

Water Intake Structures for Hydropower

Dritan Bratko1, Alban Doko2

1Department of Hydraulic and Hydrotechnic, Universiteti Politeknik i Tiranes, Albania2Department of Hydraulic and Hydrotechnic, Universiteti Politeknik i Tiranes, Albania

1 ABSTRACT

In the age of industrial development, lakes, rivers andcanals have been exploited to an ever increasing extent, anddams and weirs for the diversion of river water have beenconstructed on flowing waterways for various purposes.Likewise, river intakes have been developed even further foragriculture and the generation of hydroelectric power. Now,when in the industrialized countries, particularly in Europe,this development has practically come to an end. In Albania avery big number of sites for large-scale and small-scale riverwater intakes are developing in the field of energy production.

The exploitation of rivers and streams requires thoroughplanning, irrespective of whether large-scale or small-scaleprojects are concerned. The ecological aspects, thecompatibility of a project with the environment and theminimization of subsequent damage caused by any measure takenare important planning criteria. For large-scale and small-scale projects, experienced planning engineers and experts arenormally appointed. In addition to the individual types ofintake structures, the necessary hydraulic and staticcalculation methods are given and explained. The prerequisitesto be met by the intake structure are different for each riverand stream, and therefore only the basics can be describedhere. The operativeness of an installation depends largely uponthe planning and, thus, upon the experience of the planningengineer. In just such a sensitive field as the intervention ina river or stream with a view to tapping water for generalpurposes, a great number of criteria are to be considered, andit is these which rare given in this planning guide.

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2 INTRODUCTION

Which is the most adequate layout plan for an intakestructure?

The most adequate layout plan is the one which allows theintake structure to function in the most effective manner whileallowing the necessary amount of water at the requiredelevation.

In this section, the design and analysis of the intakestructure elements, which influence the effectiveness ofconveying water to the turbine, have been treated. The purposeof hydraulic calculation for all the elements of the intakestructures with or without pressure is that the designers havethe possibility for optimization of the hydraulic scheme of asmall hydropower plant, and water to be conveyed to the turbinewith lower costs and high efficiency.

Traditionaly, the intake structures for the hydropowerplants were the structures conveying water from a systemwithout pressure to one with pressure. In this study thedefinition of “intake structure” includes not only thetraditional ones but the ones which serve to the systemswithout pressure as well.

Intake structures can be categorized as:•Intake structures which take water directly from the water

flow and pass it to the penstock.•Intake structures which take the water through an

auxiliary structure which diverts the flow•Intake structures placed on reservoirs•Intake structures which act as flow regulators

3 DESIGN CRITERIA

The effectiveness of a hydropower plant is directlydependent on the location, orientation, and the water level atthe intake structure. In order to have satisfactory and correctresults, the hydraulic structures should be adapted to thesite. Factors that are considered include:

3.1.1 Water levels

In most of the cases the intake structures should bedesigned in order to function for different water levels.

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For the intake structures placed on reservoirs, studiesshould be conducted in order to determine the fluctuations ofthe water level. The efficiency of the structure should bechecked for the normal and extreme levels. It can be acceptedthat the effectiveness of the structure may be lower in thecase of maximal levels if they have short time span.

The intake structures placed in rivers or streams aredetermined from the water level of the flow, which isdetermined by hydraulic studies. The influence of the intakestructure or the diversion structure on the water levels in theriver or stream, the erosion and deposition, the ice blockageetc., should be evaluated. The narrowing or widening of theriver at the intake structure should be evaluated as well.

The hydraulic parameters which should be taken intoconsideration are:

The possible velocity, the aeration of flow, the arrivalvelocity and the hydraulic losses. These parameters usuallytake critical values for low water levels, and as a result theaverage velocity and submersion are significantly reduced.

3.1.2 Placement distance

The distance between the intake structure and thepowerhouse influences the hydraulic losses as well as the costof the conveyance structures. Most of the powerhouses areconstructed near dams or diversion structures in order toprofit as much as possible in water head, while the intakestructures are placed on the lowest point of the reservoirs. Inthe cases when the powerhouse is at a considerable distancefrom the intake structure: is done an evaluation of the wholediversion system in order to have as few losses as possible.

3.1.3 Geological composition

Bank stability is important, and the intake should belocated in a reach of river where the bank is stable because anunstable bank is likely to adversely affect intake performance.Foundation conditions also may affect design. If possible, theintake should be located at a site possessing favorablefoundation conditions because overcoming adverse foundationconditions may require costly treatment.

Careful study of site geometry, relationship to otherprincipal project features, geotechnical and environmental

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factors, and river regime will lead the designer to select theappropriate general arrangement and will suggest those featuresto be included in the intake's design.

3.1.4 Diverted flow

While placing the intake structure, the diverted flowshould be taken into consideration. Intakes are generallyoriented to minimize separation of flow which causes portionsof the intake to be ineffective and can result in swirl,eddies, and vorticity which may entrain air. Where the rate ofwithdrawal is small and the intake relatively deeply submerged,flow separation, vorticity, and air entrainment arc less likelyto occur. Higher withdrawal rates are more conducive to flowseparation than lower rates.

3.1.5 Sediment

The intake structures should be placed in such a way tominimize the accumulation of fine materials. The intakestructures in reservoirs are placed over the calculatedalluvial accumulation level for the lifespan of the structure.In other projects, the transport of sediment into theconveyance, forebay, and intake may cause sediment accumulationin the intake approach, resulting in higher approachvelocities, increased head losses, and potentially causing flowseparation. Where the accum uJation is severe, removal may berequired at periodic intervals. The passage of sediment throughthe unit may result in undesirable wear of the turbine runnerand this should be minimized

3.1.6 Ice

Ice is a major hazard for intake structures as in cases of:trash rack blockage, increase in hydraulic losses, reduction ofthe diverted flow, and additional measures for its cleanup. Theplacement of the intake structures in order to minimize theproblem of ice, requires a detailed study of the annual iceregime. The general principles are to locale the intake whereice flows are minimal and to provide facilities for passing icethrough the project such as ice sluices and overflow sectionsor gates. Another approach is to locate the intake in an areawhere an ice cover is likely to form.

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4 POWER INTAKE

Power intakes are structures which convey water from asystem without pressure in one with pressure. There are twobasic power intakes: vertical and horizontal.

4.1 Vertical intake

Vertical intakes are commonly used where there is a greatdifference in elevation between the reservoir bottom at theintake and the turbine, and where the penstock or power tunnelis vertical for some distance to the level of the powerhouse.

The dimensions of the vertical intake are conditioned fromthe penstock diameter or the power tunnel diameter. Thisdiameter is determined from the comparison of the energyproficiency to the construction cost. The main criteria for thestructural dimensioning are the minimization of the hydrauliclosses and the avoidance of eddies. The vertical intake can bepositioned near upstream slope or near the banks which do notinfluence the passage of water into the structure and are alsoprotected against erosion.

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a) b)

Figure 1 Vertical intakeHydraulic losses caused by the vertical intakes:

(1)

hydraulic losses from the water surface level to thediametric constant of the intake (m)velocity in the penstock (m/s)the loss coefficient which varies from 0.1 up to 0.3

The adequate shape of the vertical intake is as shown inthe figure:

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The equation for the entrance shape which is derived fromlaboratory tests is:

(2)

discharge (m³/s)distance between the water surface and the plan where

we want to determine the radius. (m)

A special care should be provided in determining if trashracks will be used or not. The racks are usually placed on theoutter perimeter of the structure where the flow velocity islow. The cleanup of the trash racks is very difficult when thewater depth is very high. But in these cases, problems withtheir blockage are not expected to occur.

The hydraulic losses from the trash racks depend on thethickness of the rods, the depth and the distance between them.

humbjed hidraulike ne zgara (trashrack head loss) (m)

(3)

shpejtesia ne siperfaqen neto te zgarave (velocitythrough the net trashrack area) (m/s)koeficenti i humbjes ne zgara (trashrack loss

coefficient)

(4)

siperfaqja neto ndermjet shufrave (net area throughrack bars) (m²)

siperfaqja bruto se bashku me shufrat dhembeshteteset (gross area of the racks and supports)(m²)

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Nje kriter i rendesishem ne funksionimin e veprave temarrjes vertikale eshte thellesia e mbytjes e cila zakonishteshte me e madhe se e veprave te marjes horizontale. Zakonishtper parandalimin e formimit te vorbullave ne hyrje te vepres semarrjes vendosen pila te cilat reduktojne shpejtesine dheshperbejne e vorbullave.

4.2 Vepra e marrjes horizontale (Horizontal intake)

(The great majority of hydroelectric project intakes arehorizontal. Even in cases where a large elevation

difference exists between the intake and the powerhouse,the intake is normally horizontal, followed by a curve to aninclined or vertical power tunnel or penstock.)

Avantazhi i veprave te marrjes horizontale eshte se ne tomund te vendosen me lehte portat, zgarat metalike si dheshandoret (stoplogs).

Veprat e marrjes horizontale ndahen ne dy grupe:

Veprat e marrjes horizontale me ngarkese te madhe ujiH>15m. (High head intakes)

Veprat e marrjes horizontale me ngarkese te vogel ujiH<15m. (Low head intakes)

Keto vepra zakonisht vendosen ne rezervuare ose ne trup tedigave hark, me gravitet, me material vendi. Ne kete rast veprae marrjes eshte vendosur direkt ne rezervuar, kemi dhe rastinkur uji nepermjet sistemeve te devijimit cohet ne nje basenpresioni ku nga aty nepermjet vepres se marrjes futet netubacionin ose tunelin e presionit .

Veprat e marrjes horizontale me ngarkese te madhe ujidergojne ujin i cili rrjedh ne tubacionin e presiont meshpejtesi nga 3-5 m/s, por dhe me shpejtesi me te larta.

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Figure 2 Horizontal intake a) direct ne trupin e diges (apobaseni te madh ujembledhes)

Figure 3 Horizontal intake b) veper marrje ne zone te kufizuar

Veprat e marrjes horizontale me ngarkese te vogel ujiH<15m. (Low head intakes)

Keto vepra zakonisht vendosen ne lumenj, ku verpa e marjeseshte e integruar ne trup te diges se bashku me turbinat.

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Figure 4 Horizontal intake, me ngarkese te vogel ujiNdryshimi midis ketyre veprave te marrjes i referohet

bilancit midis humbjeve hidraulike qe shkaktohen ne veper dhekostos se saj.

Ne verprat e marrjes me ngarkese te madhe uji humbjethidraulike jane relativisht te vogla kundrejt renies dhekostoja per rritjen e permasave te vepres se marrjes per tezvogeluar shpejtesine nuk eshte e nevojshme.

Ne veprat e marrjes me ngarkese te vogel uji humbjethidraulike kane nje ndikim te madh ne energjine e prodhuar. Neketo vepra eshte e arsyeshme rritja e permasave per te ulurshpejtesine.

4.2.1 Pjeset perberese te veprave te marrjes horizontale

Vendosja dhe konstruksioni I zgarave. (Trashrack locationand design)

Varet nga menyra e punes se zgarave, do kene te montuar njepastrues mbeturinash automatic ose do pastrohen ne menyremanuale. Menyra e pastrimit varet nga sasia e mbeturinave qepritet te grumbullohen. Per nja pastrim sa me te lehte zgaratvendosen te inklinuara 1H:4V. Ne veprat e marrjes me ngarkesete madhe uji zgarat instalohen pak para hyrjes . Dherekomandohet qe shpejtesia e rrjedhjes se ujit nepermjetzgarave nuk duhet te kaloje shpejtesine 0.8-1.2 m/s. Ne rastetkur kemi akull rekomandohet qe zgarat te jene te zhytura nganiveli normal I ujit 0.5-1m dhe te kene nje mur mbrojtes ne ktelartesi.

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Forma e hyrjesZakonisht I afrohet trajektores qe pershkon rrjedha e

ndrydhur. Pergjithesisht ka formen e nje kembane. (bellmouth).Por mund te jete dhe drejtkendeshe e cila ngushtohet me pasderisa arihen permasat e tubit.

Ne rastin e (low head intake) kur turbina eshte e integruarne trupin e diges per parandalimin e geryerjes (cavitation) sesaj gjeometria e vepres hyrese percaktohet nga prodhuesi Iturbinave.

Zona tranzitoreGjatesia e kesaj zone bazohet ne kushtin e ruajtjes se

pershpejtimit sa me kostant te rrjedhes. Ne rastet kur kemidisa hapesira te cilat ndahen ndermjet tyre me ane te pilavemund te nevojitet nje zone tranzitore me e gjate dhe gjithashtume e gjere se ne rastet kur kemi nje hapesire.

Shandoret (Bulkheads or stoplogs)Vendosen zakonisht ndermjet sgarave dhe portave te

sherbimit ne rastin e demtimit te ketyre te fundit. Vendosja etyre behet nepermjet udhezuesave te krijuar ne muret e vepreste cilet vendosen ne fillimin ose mbarimin e kurbezimeve.Humbjet hidraulike qe shkaktohen nga shandoret varen ngadimensionet e udhezueseve. Sa me I madh te jete seksioni Ishandoreve aq me te vogla do te jene shpejtesite por do kemiritje te kostos.

Portat e sherbimitMund te vendosen ne pjesen e kurbezuar ose ne mbarimin e

saj. Vendosja e portave behet nepermjet udhezuesave te krijuarne muret e vepres. Portat mund te jene me ngritje mekanike oseautomatike. Portat perdoren ne rastet e problemeve te ndryshmete cilat mun te ndodhin ne veper ose tek turbinate. Dimesionete portave percaktohen nga hapesira e cila duhet te mbulojne,gjithashtu nje dimesionim me I madh I portave ndikon ne humbjethidraulike per kte arsye duhet bere nje krahasim ekonomoikndermjet humbjeve dhe energjise se fituar.

Tubi I ajrimitAir vents are typically included in forebay or intake

designs that incorporate power conduit and some type gatevalve. The function of an air vent on a guard gate is to

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provide air into the downstream power conduit so that theconduit does not experience unacceptable vacuum pressures whenthe gate is closed during standard flow conditions. Thesevacuum pressures have been known to cause conduit collapse inunvented or poorly vented conduits, in extreme cases. Theaddition of air downstream of a closing gate also reducesnoise, cavitation and vibration in the conduit and otherdownstream systems.

4.2.2 Llogaritja hidraulike e vepres se marrjes horizontale.

Humbjet hidraulike jane nje nga faktoret kryesore nefunksionimin me efektivitet ose jot e nje skeme energjitke.Humbje hidraulike ndodhin nga pikat e devijimit te ujit ngarrjedha ne sistemin transportues , dhe ne vepren e marrjes mepresion ku humbjet shkaktohen te zgara, hyrja e vepres,udhezuesit e portave dhe shandoreve. Eshte e rendesishme tevleresohen te gjitha humbjet hidraulike.

Zgara metalikeA trash rack is required at the entrance of penstock to

avoid the entrance of floating debris. The flow water throughthe rack also gives rise to a head loss. Though usually small,it can be calculated by a formula developed by Krischmer:

head loss (m)

(5)

bar thickness (mm)width between bars (mm)approach velocity (m/s)angle of inclination from horizontal (°)

Where the parameters are identified in figure 5.

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Figure 5 format e pershtateshme te zgarave metalike

This formula is valid if the length L of the bars issmaller than 5 times their diameter. If the grill is notperpendicular but makes an angle with water flow. The resultof equation 5 should multiplied by correction factor provided in table 1.

Table 1 Correction factor t/b

1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

0º 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.0010º 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.14 1.5020º 1.14 1.16 1.18 1.21 1.24 1.26 1.31 1.43 2.2530º 1.25 1.28 1.31 1.35 1.44 1.50 1.64 1.90 3.6040º 1.43 1.48 1.55 1.64 1.75 1.88 2.10 2.56 5.7050º 1.75 1.85 1.96 2.10 2.30 2.60 3.00 3.80 -----

--60º 2.25 2.41 2.62 2.90 3.26 3.74 4.40 6.05 -----

---

Submergence DepthMinimum submergence depth at penstock inlet is required.

There are different formulas for minimum depth at the inlet toavoid vortices and air entrainment:

(Knauss) (6)

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(Rohan) (7)

(Gordon) (8)

c=0.74245 and 0.5434 for non-symmetric and symmetricapproach

penstock diameter (m)submergence depth (m)flow velocity in penstock (m/s)

Figure 6 Submergence Depth

Format e hyrjesPer te minimizuar humbjet hidraulike dhe per te shmangur

zonat ku mund te kemi geryerje, hyrja e vepres se marrjes duhette kete forme te tille qe te shkaktoje ndryshime graduale nerrjedhjen e ujit.

Bazuar ne studimet dhe provat laboratorike eshte aritur neperfundimin se forma qe kenaq kushtet e mesiperme eshte ajo neforme kembane.

(9)

Per nje hyrje rethore

Per hyrje drejtkendshe ose katrore

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Suppressed bottom and side contractions

Suppressed one side only, for unsuppressed side

Ku: X dhe y jane boshtet koordinative. Boshti x-x eshte Izhvendosur parallel me aksin e tubit me vleren 0.65Ddhe y-y eshte pingul me aksin e tubit I zhvendosur0.5D nga hyrja.

Head losses for intake entranceHead losses for intake are represented by equation:

entrance head loss (m)

(10)

The value of C may vary from 0.97 for intake curvatureclosely approximating the free jet trajectory to as low as 0.8.Values as low as 0.5 or 0.6 can be obtained for very poorintakes with no curvature

Table 2 Coefficient for different forms of entranceIntake Condition 1/(C²-1)Well-designed bell mouth 0.04-0.05Well rounded 0.1Slightly rounded 0.25Square edged 0.47-0.56Projecting 0.62-1.0

Head loss due to slotsBased on hydraulic consideration E. Mosonyi suggests the

following approximating formula for the calculation of the headloss at the slots:

Head loss due to slots (m)

(11)

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Cross-section coefficient

(12)

Weisbach coefficient

(13)

velocity in the entrance flume, just before the slots(m/s)

width of entrance flume (m)depth of entrance flume (m)width of slot (m)depth of slot (m)

If then If then

The disturbing effect of the opening necessary for thehoisting of the gate is accounted for by dimension

(14)

Representing the widening of the cross-section.

Tubi i AjrimitTubi I ajrimit mund te dimesionohet simbas disa menyrave: A

rule of thumb used for sizing air vent piping is to providefrom one half to one percent of the area of the power conduitas an air vent. Dhe me ane te formules te meposhtme.

Area of air vent is :

(15)

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flow of air through inlet ( usually set equal toconduit flow) (m³/s)

coefficient of discharge through air inlet, values ofc range from 0.5 for ordinary air-inlet valves to0.7 for short air-inlet valves.

area of air inlet (m²)thickness of power conduit (mm)diameter of power conduit (mm)safety factor for collapse of power conduit, use s=5for buried conduit and s=10 for exposed conduit onsaddlesconversion coefficient from US unit to SI (0.305)

5 VEPRAT E MARRJES PA PRESION (CONVEYANCE INTAKE)

Veprat e marrjes pa presion jane ato struktura te cilatbejne kalimin e ujit nga nje system pa presion ne nje systemtjeter pa presion sic mund te jene kanalet, tunelet pa presionetj.

5.1 Lateral Intake

Veprat e marrjes anesore zakonisht hasen ne dy tipe:

Vepra marrje anesore te cilat marin ujin nepermjet njevepre ndihmese. (lateral intake with damming up of theriver). (Kto vepra perbehen nga vepra devijuese e cilaeshte nje dige, dhe vepra e marrjes).

Veprat e marrjes anesore te cilat marrin ujin direct ngarrjedha. (lateral intake without damming)

Kto vepra zakonisht perdoren ne rastet kur kerkohen sasi tevogla uji. Sasia e ujit te devijuar prej tyre varet ne menyredirekte nga thellesia e ujit ne lume. Prurjet qe mund tedevijohen prej ketyre veprave jane 1-2 m³/s.

5.1.1 Lateral intake with damming up the river

Keto vepra jane gjeresisht te perdorura ne skemat eshfrytezimit te lumenjve dhe perrenjve me pjerresi shtrati0.001%-10%.

Qellimi I ndertimit te ketyre veprave eshte:

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Te parandalojne, ose te reduktojne depozitimin ematerialit te imet ne kanalin e dergimit.(conveyancechannel)

Vepra e marrjes keshillohet te vendoset ne kthesen ejashtme te lumit te lakuar, ne kte pjese krryma ka shpejtesineme te madhe dhe depozitimi I materialeve eshte shume I vogel.

Figure 8 zona me vend depozitime te mundeshme te materialeveinerte qe sjell lumi

Per te mos lejuar futjen e depozitimeve ne vepren emarrjes, para saj ndertohet nje kanal i ceket. I cili ndertohetme nje pjerresi 2%-5% , disnivel nga shtrati I lumit 1-1.5m dheshoqerohet me nje porte e cila hapet sa here duhet te pastrohenketo depozitime.

Te marrin sasine e kerkuar te ujit duke patur humbjehidraulike minimale.

Dimesionimi I hyrrjes se vepres se marrjes duhet te jete Itille qe te mos kemi shpejtesi me te medha se 0.8-1.2 m/s.Gjithashtu duhen patur parasysh humbjet hidraulike qeshkaktohen duke I dhene nje forme sa me te pershtatshme. Njefactor I rendesishem eshte dhe drejtimi I vepres se marrjes nelidhje me aksin e lumit. Per te komanduar sasine e ujit qefutet ne veprebn e marrjes si dhe per te bllokuar ate ne rastedefektesh vendosen porta, dhe shandore.

Te ndaloje hyrjen e akullit dhe materialeve e ngurta nekanalin e dergimit.

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Per te ndakuar hyrrjen e materialeve te ngurta ne vepren emarrjes instalohen zgarra metlike te inklinuara 1H:4V te cialtmund te pastrohen ne menyre manual ose automatike.

Per te mbrojtur vepren nga akulli keshillohet qe vepra emarrjes te vendoset ne anen e brendshme te ktheses. Ne pjesen esiperme te hyrrjes se vepres se marrjes vendosen mure vertikaleose te pjerret te zhytur ne nje thellesi 0.5-1m kundrejtsiperfaqes se ujit.

Figure 9 planvendosja optimale e nje vepre marrje anesore

5.1.2 Llogaritja hidraulike e lateral intakes.

Drejtimi I vepres se marrjesBazuar ne studime te ndryshme te kryera nga D.Y.Sokolov

kendi I drejtimit te vepres se marrjes percaktohet nga formula:

(16)

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koefficenti I ndrydhjes se rrymes ne hyrrjen e vepresse marrjes (m³/s)

(17)

gjeresia e rrymes se ndrydhur (m)gjeresia e kanalit te dergimit (m)prurja e lumit (m³/s)prurja qe mer vepra e marrjes (m³/s)thellesia e ujit ne lume ose perrua (m)

thellesia e ujit ne vepren e marrjes (m)

Figure 10 forma teorike e levizjes se ujit

Dimesionimi I hyrrjesSiperfaqja e kerkuar ne hyrrje te vepres se marrjes

llogaritet me formulen:

(18)

preferohet 0.8-1.2 m/s

5.1.3 Humbjet hidraulike

Humbjet ne hyrrje mund te llog me ane te formules:

20

(19)

varion nga 0.8-0.4 ne varesi te kendit te drejtimit tevepres ku vlerat me te medha mund te meren ne rastin e kendevete ngushta

shpejtesia e rrjedhes ne lumeshpejtesia e rrjedhes ne vepren e marrjes

Ne rastin kur mund te kemi nje dhemb ne hyrrje dhe mureanesore ose pila te rrumbullakosura humbja maksimale ne hyrrjellogaritet:

(20)

Humbjet hidraulike per shkak te zgarave, udhezuesave teportave jane trajtuar tek veprat e marrjes me presion.5.2 Drop intake

Drop intake or Tyrolean intakes are commonly used for smalland steeply sloped mountains rivers with reliable rockfoundation. This type of intake consists essentially of achannel built in the river bed, stretching across it andprotected by a trash rack with a sloping face oriented in thedirection of the river flow.

Figure 11 format e pershtateshme te zgarave metalike

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5.2.1 Trash rack

Trash rack function essentially as filters to removematerial and stones, floating on or just below the watersurface from enter into the intake. In design of the trash racktype and dimensions precautions should be taken to preventclogging of the racks. The basic design variables of the trashrack are the opening between adjacent bars ‘a’ and the centerspacing ‘b’. These values for SHP depend on the size ofmaterial allowed to pass through the intake. Fig. 12 shows sometypes of rack bars with different profiles.

Figure 12 Typical profiles of racks for Tyrolean intake

The rectangular racks are not recommended to be used forintake as they are easily and rapidly clogged by stones. Fig.12a. The bulb-ended bars have better performance and are morerigid if required Fig. 12b. The best shape is round-head barsthat prevent sediments from jamming and have better resistanceagainst impact of stones because of higher moment of inertiaFig. 12c. So, this last type of bars should be usedsystematically for Tyrolean intake. The recommended openingrack bars for this type is 20 to 40 mm.

The racks have to be inspected and cleaned at regular timeintervals to prevent potential obstruction by debris.

5.2.2 Design criteria

The dimensions of the Tyrolean intake must be sufficient tocapture all the water for the design discharge. According tothe shape of the trash rack, head losses, approach flow regime

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and design discharge, the dimensions of a Tyrolean intake arebased on following formula:

(21)

intake length over the trash rack (m)trash rack width (m)design flow (m³/s)water depth at upstream end of the trash rack (m)

(22)

critical height (m)

(23)eh initial water height (m)

correction factor

(24)

discharge coefficient for trash rack

Figure 13 vlerat e koeficentave sipas formave te zgarave

trash rack coefficient

23

(25)

slope angle of the trash rack (º), opening between the bars (mm)center spacing of bars (mm)

In order to guarantee the diversion of the minimum amountof water when stones become wedged in the trash rack, orbranches and leaves remain on the trash rack at low waterlevels, the trash rack should be selected:

(26)

6 CONCLUSION

This section should state the most important conclusions ofthe paper.

7 REFERENCA

[1] Emil Mosonyi,(1987) Low-Head Power Plant., Akademia Kiado,Budapest.

[2] Emil MosonyI,(1991) High-Head Power Plant, Volume IIA.,Akademia Kiado, Budapest.

[3] American Society of Civil Engineers,(1995) Guidelines forDesign of Intakes for Hydroelectric Plants

[4] American Society of Civil Engineers,(1969) CivilEngineering Guidelines for Planning and Designing HydroDevelopments Volume 4 Small Scale Hydro

[5] European Small Hydropower Association 2004, Guide on How toDevelop a Small Hydropower Plant

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[6] Mohammadreza Andaroodi,(2006) Standardization of CivilEngineering Works of Small High-head Hydropower Plants andDevelopments of an Optimixation Tool

[7] Helmut Lauterjung & Gangolf Schmidt,(1989) Planning ofWater Intake Structures for Irrigation or Hydropower. APublication of GTZ-Postharvest Project in: DeutscheGesellschaft für Technische Zusammenarbeit (GTZ) GmbH.

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