High Head Small Hydro

8/10/2019 High Head Small Hydro

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High Head Small Hydro

a dissertation

by

J. L. Gordon, P.Eng.

This presentation includes design suggestions developed from experience with the detaileddesign of 6 high head small hydro plants in Bolivia and Madagascar, and 2 larger high headpowerplants in Canada, and Sri Lana! "n this case, small hydro is defined as any powerplanthaving an installed capacity of less than #$M%, and a flow less than 2$m&'s!

Two (xcel )* computer programs are included in the C+-.M! .ne provides a method of

comparing the si/e, efficiency and cost of three alternative tur0inegenerators powered 0yhori/ontal axis 21et elton units, hori/ontal axis 31et Turgo units, and either hori/ontal or verticalaxis 4rancis tur0ines! The other computer program provides a preliminary si/ing for a surge tan!

prepared for a workshop on

International Small Hydro Opportnities

organi!ed by

"atral #esor$es %anada

in $on&n$tion with the

International Energy 'gen$y

Hydropower Implementing 'greement on (e$hnologies and Programs

at

Hydro)ision *++*, Portland, Oregon, + Jly

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Introd$tion.

5 high head small hydro plant implies generation from small flows! 5t the upper limit of capacity,at #$M%, and assuming a head of &$$m, the flow reuired is less than 2$m &'s! at this flow7 therelative cost of the powerhouse and euipment 0ecomes a smaller proportion of the totalinvestment! The ma1or proportion of cost is usually associated with the conduit from the intae to

the powerplant! This contrasts with low head hydro, where most of the cost is for the euipment!

'$$ess roads.

8igh head hydro plants are 0uilt in mountainous terrain! Construction of an access road in suchterrain is 0oth expensive and time consuming! The 9ongo -iver valley in Bolivia, is a primeexample of the difficulties encountered 0y road 0uilders! 5 gravel road reaches the valley over amountain pass at (l! :,*2$m! "n the valley, the road descends through several hairpinswitch0acs to the reservoir for the first powerplant 9ongo, at (l! :,6&:m! There are ; morepowerplants on the river, with the last at 4altani, with a tailwater at (l! ;66m! The plants were 0uilt0etween 3)2; and 3)):! (xcept for 4altani, all are euipped with impulse units! +istance 0y riverfrom the 9ongo -eservoir to the 4altani tailrace is only &&m! 5verage river gradient is 33!:< =3>!

4or the last 6 powerplants, the construction schedule started when the access road reached thepowerhouse site! ?o attempt was ever made to impose a schedule on the road construction! "tusually reuired a0out 3 to 2 years to traverse a0out 2 to #m! 5s the resident engineer remaredto the author @with the river descending at an average gradient of 3&


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/i)ersion weir.

Most high head small hydro installations are runofriver, with storage provided on any suita0lelae upstream! The dam is only a low diversion weir, designed to open fully to pass the 0ed load!The most common design used to comprise a concrete weir across the river, less than 2m high,topped with flash0oards or stoplogs! The upstream face of the concrete section would have a

slope of a0out 6 hori/ontal to one vertical, and covered with old steel railway rails, to spread theimpact of 0oulders rolling over the weir!

Currently, this design has 0een moderni/ed, 0y using inflata0le ru00er dams to replace thestoplogs! +uring a flood, the ru00er dams are fully deflated, thus providing no impediment to thepassage of 0ed load! 5ny designer unfamiliar with the concept, should tae time to visit theMamuam weir and intae, a0out one hour 0y car north of ancouver, Canada! There, two ru00erdams across the river, divert water to a #$M% powerplant! The weir dam was designed 0y 5cres"nternational, 0ased on a hydraulic model study! The Mamuam -iver carries one of the highest0ed loads per cu0ic meter of flow of any river in Canada!

There are a few rules for designing diversion weirs on mountain streams! These areD

The diversion weir should not impose any o0struction to the passage of 0ed load!

The weir crest should not 0e a0ove the average river 0ed level! "f a0ove, the river0ed will fill with 0ed load to weir crest level!

-u00er dams =preferred>, or fish0elly flap gates, or stoplogs can 0e used to increasethe water level a0ove the crest of the concrete weir!

The weir should have the same width as the river, 0an to 0an!

5 set of widely spaced racs, set at right angles to the flow, and immediatelyupstream of the weir, should 0e used at the entrance to the intae channel! The racspacing should 0e set to inhi0it the entry of 0oulders!

5 small sluice gate can 0e placed immediately downstream of the entrance to theintae channel to flush out de0ris and 0ed load!

The intae channel should lead to a sand trap, with a low sluice outlet, and a weir tothe intae tan and trashracs! The sand trap wall, on the river side, could 0e usedas a weir to discharge flood waters 0ac to the river!

The design should 0e such that minimal damage will occur on overtopping 0y a largeflood! The ru00er dams and sluice facilities could then 0e designed for the passageof a relatively small flood having a freuency in the range of 3'$$ to 3'#$$!

"f the site conditions are difficult, with 0ends in the river immediately upstream, a hydraulic model

study of the weir and intae may 0e necessary! 5n illustration of the complexity such a sand trapfacility can acuire is provided 0y the Corani development, where the -io into side streamintae has a roc trap, gravel trap and finally a sand trap! The design was 0ased on a hydraulicmodel studied at the San 5ndres Eniversity in La a/, Bolivia =2, &>!

Intake.

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The generating euipment on a high head hydro plant is relatively small! 4or example, at a headof a0out &$$m, and with 2 units in a 2#M% powerplant, there is the choice of using either 4rancisor impulse units, as illustrated 0y the attached program, from which it can 0e determined thatD!4rancis units would have a 3#0lade runner with a throat diameter of a0out ;2)mm, and rotate at)$$rpm! -ac spacing at 2!2#< of runner diameter, would 0e only 3;!6mm!

"f the units were hori/ontal axis, 21et impulse tur0ines, the runner would rotate at &2*!&rpm! andhave an outside diameter of 263)mm! Fet diameter would 0e 2$#mm! -ac spacing at $!2 times

1et diameter, would 0e :3mm!

This illustrates two pointsD

-ac spacing is very close on high head units, resulting in easy 0locage from anaccumulation of grass and twigs!

"f rac spacing is a criterion, impulse tur0ines are preferred! 8owever, in thisexample, the cost preference would 0e for 4rancis units!

+ue to the narrow rac spacing resulting in rapid clogging with floating leaves and twigs, it isprudent to have a generous rac area, and to install an automatic rac cleaning machine, or allowfor manual cleaning! "f there is a large volume of floating material, consideration should 0e givento using a gathering tu0e type of intae, where the top of the racs are su0mersed a0out 3m!0elow water level, and are very long with a height of a0out a meter, as at the #6M%, 23:m head

5ndealea development in Madagascar =:, #>, and at the 6!&M%, ;;m head Maggottydevelopment in Famaica! 5t 5ndealea, the intae design proved particularly difficult to resolve,since there was a 0end in the river immediately upstream, a heavy 0ed load, and a large floatingde0ris load from the tropical forest! 5 series of tests with a hydraulic model was necessary, andseveral configurations had to 0e tested, 0efore a successful design was produced!

There is always a discussion a0out the type of gate reuired in high head developments! Sincethere is usually a tur0ine valve to provide the second line of defense in flow control, it can 0eargued that a simple sliding 0ulhead gate is adeuate at the intae! (xcept for tunneldevelopments, the author favors the use of a wheeled gate, capa0le of closure without power

against flow! The reason for this, is the distinct possi0ility of pipe or penstoc rupture! (ven ifthere is a control valve at the penstoc inlet, failure of this valve to operate on excess flow ispossi0le due to poor maintenance of the controls!

%ondit optimi!ation.

Since the water conduit usually comprises a ma1or proportion of the pro1ect cost, determination ofthe optimum conduit diameter is important! There are a few @rules of thum0A for determination ofthe most economic conduit diameter, at the prefeasi0ility stage, as followsD

4or energy generating plants, where the plant capacity factor is in the region of 6$

To clarify these statements, assume a peaing pro1ect with a gross head of &$$m! %ith theallowa0le loss in the conduit set at *


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pressure tunnel to the surge tan, followed 0y a )$$m long penstoc, total conduit length is&,)$$m! 5llowa0le losses in the tunnel and penstoc are calculated as followsDLoss in the penstoc at twice the loss in the pipe is G 23 x )$$ x 2 ' H&$$$ I =)$$ x 2>J G *!;*#m!Loss in the lowpressure pipe is G 23 *!;*# G 3&!32#m! Chec, loss per meter of penstoc G*!;*#')$$ G $!$$;*#m! Loss per meter of pipe G 3&!32#'&$$$ G $!$$:&*#m!

Knowing the allowa0le loss, it is easy to calculate the conduit diameter! 5lso, since loss isproportional to the diameter raised to the power of #!&&, a small change in diameter has a verylarge effect on the loss! This procedure is adeuate for a prefeasi0ility assessment!

%here there is only a penstoc, the preliminary diameter can 0e o0tained from formulae such asthose developed 0y 4ahl0usch =6>!

5t the feasi0ility design level, the operating mode should 0e nown! Then a determination of theannual energy loss for each load level should 0e undertaen, for a range of diameters, to arrive atthe optimum diameter! ?ote that an energy plant will not 0e operating at full load for many hoursper annum! 5lso, since loss is proportional to flow suared, a high loss at full load for a short timecan 0e tolerated! By undertaing such a detailed analysis, the author has encountered a fewinstances where the penstoc diameter on energy pro1ects could 0e reduced!

Such is not the case in a peaing plant, where most generation taes place at full load! Thisillustrates why the load pattern must 0e nown with accuracy, for an assessment of the optimumdiameter!

5t the feasi0ility design stage, it is usually adeuate to start with a detailed costing of the conduit0ased on the diameter selected using prefeasi0ility rules of thum0! The cost of other diameters isthen estimated using a lower unit price for the incremental wor! "n a spreadsheet, this can 0eachieved 0y using an exponent 0etween $!6 and $!) in a cost formula! 4or example, if the cost of3$$,$$$m&of excavation is 3 million, the cost could 0e represented 0y the formula Cost G x3$$,$$$y, where x and y are interconnected! "f the exponent y G $!;, then x G 3$$, and cost G 3million! 5n exponent of $!; means that the cost of 32$,$$$m&of excavation is 3,3#*,$$$ and theincremental cost of the additional 2$,$$$m&is *!;#'m&!

"n effect, the incremental unit cost is reduced 0y 23!#

Intake $anal, lowpressre pipeline and tnnel.

5 canal in mountainous terrain is 0oth expensive to construct, and difficult to maintain!Maintenance difficulty arises from erosion material falling down the uphill side of the slope, to endin the canal! "n Bolivia, the small canals are constantly patrolled and any de0ris encountered isremoved 0y hand! "n areas where experience has indicated that de0ris volume is large, the canalis covered with tim0ers! Based on the authors experience, canals should 0e avoided! They canonly 0e 1ustified where there is ample la0or for construction and maintenance!

Tunnels are the preferred means of moving water to the penstoc! 8owever, the minimum si/ehas to 0e taen into consideration! The smallest tunnel section that can 0e constructed withstandard rail mounted euipment is an inverted Eshape having a width and height of a0out 2!#m!

5ny reinforcement of the tunnel can 0e added within this section! 5t Corani, in Bolivia, the finalsection has a width of 2!$#m and height of 2!2#m =2>!

Construction experience with the tunnels in the 9ongo valley, showed that it was prefera0le to0uild the access road on one side, and the tunnel on the opposite side of the valley! This was dueto the very steep mountain slopes, averaging a0out :# degrees! 5ccess to the tunnel was

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o0tained 0y ca0le from the roadside, to portals on the opposite slope, at a0out ;$$m intervalsalong the tunnel! The ;$$m interval is 0ased on the :$$m distance men can move a loaded tructo the portal, since it was not possi0le to lift power euipment to the tunnel on the ca0leway!+isposal of tunnel muc was always a ma1or concern! Most muc ended up in the river, since anyattempt to leave the material on the mountainside, usually resulted in the material 0eing washeddown the mountain during rainstorms!

Low pressure pipes can also 0e used to convey water to the penstoc! "f pipes are used, thepreference is for a 0uried design, again due to the high possi0ility of damage from 0oulders andother erosion material descending from the upper slopes! "n selecting the route, a ma1orconsideration is the means of traversing the numerous gullies encountered on the mountainside!The preferred means is 0y a selfsupporting pipe 0ridge, with enough clearance 0elow the pipe toallow for the passage of 0oulders and de0ris 0eing washed down! 50utment supports are usuallyexpensive, since moving concrete to the area is often difficult! 4or this reason, gully crossings arecostly, and are usually underestimated! "n the authors experience, a tunnel is often the mosteconomic alternative in steep terrain!

Peaking storage.

%here there is a long tunnel, the tunnel itself can sometimes 0e used for peaing storage, as at8arca =3> where side cham0ers to the tunnel have 0een 0uilt with a section :m wide 0y :!)mhigh, a0out dou0le the width and height of the normal tunnel section! 5lternatively, a small pondcould 0e developed in a gully off to the side of the tunnel as at Chururaui in Bolivia =*>!

5t Chururaui, the peaing pond is divided in two, 0y a weir with a 0ottom flap gate, designed toopen when the water level on the large upstream pond is a0ove that in the lower smaller pond!The intae to the penstoc is connected to the lower pond! 4low from the tunnel enters the smalllower pond, uicly filling the pond, and flowing over the weir into the upper pond! %hen theupper pond is filled, and when the pea demand starts to exceed flow from the tunnel, the waterlevel in the lower pond starts to fall, draining the tunnel! Simultaneously, the upper large pond isdrained through the low level flap gate, providing peaing flow!

The weir 0etween the two ponds increases head on the tur0ines as soon as the pea demand

period is over, and tunnel flow exceeds tur0ine flow! The higher head is maintained throughoutthe pond filling cycle, increasing energy generation!

Srge tank.

5 surge tan is usually reuired at the end of the lowpressure pipeline! .n some impulsepowered developments, the tan has 0een omitted! This results in extremely long needle valveopening times, sometimes in the order of several minutes! This is too long for the units to 0ecapa0le of operating in an isolated mode! 5lso, due to the very slow opening, synchroni/ing of theunits may have to 0e accomplished with a 1et deflector! This situation adds complexity to thecontrols, and must 0e disclosed to the 0idders at tender call!

5 program for preliminary si/ing of a restricted orifice surge tan is contained in the C+-.M!

The program calculates tan diameter, si/e, roc excavation, concrete and formwor uantities ifin roc, and weight of steel if the tan is elevated a0ove ground! 5 copy of the program is shownon the next page! "nput data includesD

3! 4lood level! 2! Low supply level!&! Tur0ine rated head! :! (levation of surge tan tee!#! +esign full load flow! 6! Epstream conduit lendth!*! Epstream conduit diameter! ;! 5verage Manning @nA!)! (rected cost of steel!

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+ue to the simplicity of the program, it is ?.T protected! Mae a secure copy 0efore use!

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0000000000000000000000000000000000000000000000000000000000000000000001igre 2. %opy of printot from srge tank program.

Pensto$k.

enstoc pipes from the surge tan down to the powerhouse can 0e either of a hyperstaticdesign, where every second 0end is unsupported and free to move, or of an isostatic design with

anchors and expansion 1oints at every 0end! 8yperstatic penstocs are occasionally used indifficult terrain, where construction of anchor 0locs is impossi0le or very expensive =;>!

(xperience with the design of the Santa "sa0el penstocs in Bolivia, has indicated that the costsavings expected from the elimination of every second anchor 0loc in a hyperstatic design, isnegated 0y the added volume in the piers and anchors! 5lso, the penstoc design is verycomplex! The addition of pipe steel stresses due to earthuae, pressure and miterdiscontinuities is difficult, and has to 0e undertaen manually, since there are, as yet, noprograms for this com0ination of stresses! 5t Santa "sa0el, the governing condition was found to

*

Srge tank si!e and $ost $al$lation. (nter data in 0lue cells only! Steel cost in cell (3#

3irginia 1alls.& 4lood level at dam, meters! G :#*!$$ Low supply level at dam, meters G :#:!$$: Tur0ine rated head, m! G 3:$ (levation at surge tan tee, meters G :&2!$$# +esign full load flow, m&'s! G 2$!2: Epstream conduit length, meters! G 23$$!$$6 Epstream conduit diameter, meters! G & 5verage Manning friction coefficientG $!$33* Conduit velocity m's! G 2!;6 Tan diameter, meters! G 6!:3; (levation top of tan, meters! G :*$!*) (levation 0ottom of tan, meters! G ::&!32) Tan height, top to 0ottom, meters! G 2*!6* Tan volume, cu0ic meters! G ;)2

3$ Steel weight in tan and legs, tonnesG #;!)3* Total height of tan, tee to roof, m! G &;!*)33 Cost of steel tan, millions of ES G $!&&) "f in roc, total tan'ris! volume, m& G )*332 -oc excavation volume, allowing for a full concrete lining of tan and riser, m&! G 3&2&3& Concrete lining volume, m&! G Curved formwor area, m2! G 662

3# Conduit area, m2 G *!$* Steel price 'g! (rected! G #!*#36 5cceleration n G $!$326# +eceleration n G $!$3$:#

3* 5ccel! head loss, m! :!6* +ecel! head loss, m! G &!263; 5cceleration c G $!#6) +eceleration c G $!&)*3) Tan area, 4 m2! G 2#!3) Tan 8'2 a0ove tee! m! G 2:!)62$ 5cceleration +eceleration23 ? acc! G 2)!*: ? dec! G 2$!*622 K acc! G :#!)* K dec! G 3)!6)

2& y acc! G downsurge G m! G #!*3 N dec! G upsurge G m! G 36!##-efD O(stimating weight of steel surge tanO 8-% ol!6, P :, Sept! 3));, pages 26 2)!-efD 8ydroelectric 8and0oo! 2nd! (d! 3)#$! %! ! Creager Q F! +! Fustin, page *&: *:&!

?ote this is a preliminary program, suita0le for si/ing and costing a restricted orifice surge tan!4or a simple tan, with no internal riser and no restricted orifice, increase the diameter 0y 2#! 4inding a location for thesurface powerhouse is dictated 0y topography any suita0le reasona0ly flat area is a candidate!"n mountainous terrain, the liely sites are often found at the confluence of rivers!

.ne important lesson learned in the 9ongo valley was to locate the powerhouse a0out 3$$mdownstream of the penstoc! The penstoc would 0e routed down the mountainside, to near riverlevel, and turn through a right angle to the powerhouse downstream! This precaution was to avoiddamage to the plant facilities from 0oulders, partially distur0ed during excavation of the penstocgrade, and later, rolling down the penstoc trench to the river!

5t 8arca, in the 9ongo valley, this danger was so extreme, that a large concrete si1ump was0uilt at the 0ottom of the penstoc cut, where it intersected a gully, to throw the rolling 0oulders upover the access road and penstoc pipe, to land in the river! The si1ump has to 0e cleanedregularly to remove accumulations of smaller rocs and other de0ris!

5nother lesson learned, was that once the water was @desandedA and clean, it made no sense todischarge the clean water into the river and headpond of the next plant downstream! "n theheadpond the clean water would mix with the dirty river water, reuiring a larger sand trap at the

downstream intae! "nstead, a canal or pipe conveys clean water from the draft tu0es to theintae, 0ypassing the headpond! This is very important during the flood season, when most ofthe sand and silt is mo0ili/ed 0y the river! +uring this period, very little flow is extracted from theriver downstream, instead the plants operate on the cleaned water from the upper powerplants!

E4ipment.

5s mentioned previously, the euipment is small! reference should 0e given to units withhori/ontal axes, since in such units, access to the tur0ine runner is easy! This is a very importantaspect, due to the erosion of the runner from silt suspended in the water, and difficult to removeat the sand trap! -unner replacement should 0e included in the operating cost! Some runnershave to 0e replaced every six months or so, others last over 2$ years! "t all depends on theefficiency of the sand trap, the extent and volume of hard uart/ particles in the water, and the

developed head =higher head G higher velocity G more erosion>!

%here the head is such that a choice is availa0le 0etween 4rancis or impulse units =includingturgo impulse units>, preference should 0e given to impulse units! "n a 4rancis unit, the wicetgates, stay vanes and runner are all eroded 0y sediment! %hile it may 0e possi0le to replacerunners on a regular 0asis, it 0ecomes more expensive to replace wicet gates, and repair stayvane erosion! .n the other hand, erosion damage to an impulse unit is usually confined to therunner, since ceramic coatings have 0een developed for impulse needles, to counter erosion!

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.ne concern with impulse units is the lower pea efficiency, and the necessity of locating thepowerplant a0ove maximum flood level! "n the authors opinion, efficiency is not a concern, due tothe very flat efficiency curve of an impulse unit, compared with that for a 4rancis unit =)>!

5s for the loss of head in an impulse unit, due to the higher powerhouse level, this is partiallycountered 0y the much lower cost of 0uilding a powerhouse a0ove water level, with no site dewatering costs! 5lso, 0y selecting hori/ontal axis impulse units, the powerhouse concrete ismostly a sla0 at grade, with concrete 0ox culverts 0elow each unit a simple design concept!

E4ipment sele$tion program.

To assist designers in the selection of appropriate euipment, an (xcel )* program is provided,specifically designed to si/e, set and cost the tur0inegenerators! 5 sample of the first page of theprogram is included on the next page! There are only ; input parameters, all easily availa0le fromsite data! These areD

3! Total powerplant flow in m&'s! Epper limit is 2$m&'s!2! +esired num0er of units in powerplant!&! ?ormal headpond or fore0ay elevation!:! Total conduit losses from trashracs to tur0ine inlet in meters!#! ?ormal minimum tailwater level, and 6! Maximum tailwater level at flood!*! System freuency, #$ or 6$ cycles, and ;! Renerator power factor!

The program calculates the total water to wire cost of the euipment, and the efficiency curve forhori/ontal axis 21et elton tur0ines, hori/ontal axis 31et Turgo tur0ines and either hori/ontal orvertical axis 4rancis tur0ines! 5 summary of cost, total capacity and pea efficiency is provided forcomparison purposes in the second part, along with a statement as to whether the unit is suita0lefor the head and flow! "n the example provided in 4igure 2, the head and flow was purposelyselected to 0e within a range where all three units would 0e suita0le!

The next three sections provide further details on the euipment, such as speed, rated head,runner and 1et diameters, and setting elevation for the tur0ine! ?ote that the 4rancis unit head will0e larger than the impulse unit heads, since the 4rancis unit can 0e set close to minimumtailwater, instead of a0ove maximum tailwater for the impulse units! 4or the 4rancis unit, the

program will also determine whether the unit will have either a hori/ontal shaft, or a vertical shaft!"f vertical, the program calculates distri0utor centerline elevation, and if hori/ontal, shaft centerlineelevation! See comment in the ad1acent cell! "ncidentally, the program can 0e used for si/ing andsetting small 4rancis units down to a head at which they are no longer suita0le!

age 2 of the program, includes efficiency charts for each unit! ?ote that if the program statesthat the unit is not suita0le, the efficiency chart and other data should 0e disregarded! Toemphasi/e this point, the water to wire cost of unsuita0le euipment will show as /ero in thesummary section! "nstead of providing a copy of each efficiency chart from page 2, all three have0een com0ined into one as shown in 4igure &, from page & of the program!

5nd 0efore it is pointed out that the efficiency for the 21et elton unit is in error, since theefficiency at $!: flow appears to 0e higher than at $!; flow, the chart is correct! %ith only one 1et

operating on a hori/ontal axis 21et unit, the lower 1et is in use! %hen 0oth 1ets are in use, thehigher upper 1et has less head, hence less efficiency, and also has higher pipe loss due to thesharp 0ends in the distri0utor to the upper 1et! The result is lower overall efficiency when 2 1ets areoperating! 4or more details, consult reference 3$!

The physical characteristics of the euipment, as calculated 0y the program are 0elieved to 0ereasona0ly accurate, to within a0out I'$!#< on pea efficiency, and to within a0out I'3!#< onthe shape of the efficiency curves! Si/e, speed and setting are also expected to 0e very close touoted parameters! %hat is not so certain, is the estimated cost! Cost is 0ased on uoted prices

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for water to wire euipment for a variety of configurations, and should 0e in the right order!Manufacturers should 0e reuested to provide a more accurate estimate!

3$


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33

8igh head small hydro tur0ine selection program (nter data in 0lue cells only, pro1ect name in 5&!

3irginia 1alls SMTS'2$$2'3Total powerplant flow, =max G 2$> m&'s! G *!#$ Comment rint pages 3, 2!+esired num0er of units in powerplant! G & Comment?ormal fore0ay elevarion for head rating, (L! =m>! G ##$!$$ Comment

Total conduit losses at rated flow, m! G 3#!$$ Comment?ormal minimum tailwater elevation, m G 2*;!;$ Comment

Maximum flood tailwater elevation, m G 2;&!#$ CommentSystem freuency, 8/! G #$Renerator power factor! =-ange $!) to 3!$> G $!)#

Total %'% Total generator ea tur0ineTur0ine axis, 1et and runner configuration! Cost ES m! capacity, M% efficiency

Comment Comment Comment8ori/ontal axis, 2 1et, 3 runner impulse tur0ine :!2*6 3#!)3* $!)$#Com0ination of capacity, head and flow is suita0le for this type of tur0ine!

8ori/ontal axis, 3 1et, 3 turgo runner impulse tur0ine &!26; 3#!*$& $!;)*Com0ination of capacity, head and flow is suita0le for this type of tur0ine!8ori/ontal axis 4rancis tur0ine 2!#)& 36!66) $!)2$

Com0ination of capacity, head and flow is suita0le for this type of tur0ine!

Hori!ontal a5is, * &et, 2 rnner Pelton implse trbine

Calculated synchronous rotational speed = rpm > G :2;!6 -ated head, m!G 2:)!$$Calculated outside runner diameter = m > G 3!;:: Fet diam =m> G $!3#&

Calculated minimum shaft centerline elevation, m G 2;#!&:Calculated pea efficiency, all 1ets operating G $!)$# ea eff! '1etG $!)&;Calculated tur0ine full load output = M% > G #!:)2 Renerator M% G #!&$6

Calculated water to wire cost excluding su0s! G :!2*6 Million ES! Comment

Hori!ontal a5is, 2 &et, 2 trgo rnner implse trbine

Calculated synchronous rotational speed = rpm > G *#$!$ -ated head, m!G 2:)!$$Calculated outside runner diameter = m > G 3!#$2 Fet diam =m> G $!23*Calculated minimum shaft centerline elevation, m G 2;#!$$Calculated pea efficiency, all 1ets operating G $!;)* ea eff! '1etG 3!6#$Calculated tur0ine full load output = M% > G #!:3; Renerator M% G #!2&:Calculated water to wire cost, excluding su0s! G &!26; Million ES! Comment

Hori!ontal a5is 1ran$is trbine Comment

Calculated runner su0mergence OSO meters G 2!#$ CommentCalculated num0er of runner 0lades G 3# -ated head, m!G 2#6!2$Calculated runner throat diameter, = d > meters! G $!#)# Speed, rpm! G 3$$$!$Calculated pea efficiency! = < > G )2!$& ea eff! G 2!)Calculated distri0utor or shaft CL! elevation, meters G 2;3!3# Comment 8ori/ontal shaftCalc! tur0ine output at rated head Q flow = M% > G #!*:; Renerator M%G #!##6(stimated water to wire cost, excluding su0st! G 2!#)& Million ES! Comment

age 3!


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1igre *. %opy of first page from e4ipment sele$tion program."nstructions on program use are included in the yellow @CommentA cells! 8old the cursor over theyellow cell, and a comment window will open!

1igre . %opy of page from e4ipment sele$tion program.

.n the a0ove chart, the efficiency curve for the 4rancis unit is shown down to $!2 flow! "npractice, a 4rancis unit can not 0e operated 0elow a0out $!: to $!# flow! The efficiency curve wascontinued down to the lower flow, to show the advantage impulse units have in 0eing capa0le ofoperating very efficiently down to very low flow ratios!

%on$lsions.

'$$ess roads. -oads in mountainous terrain are 0oth expensive to construct, and difficult toschedule! 5 generous contingency for additional cost and time should 0e included in the design!

-edload and sediment. This has to 0e excluded from the water passages 0y gravel and sandtraps! 4ailure to exclude sediment, will result in rapid deterioration of the tur0ine runner!

/i)ersion weir. "t is prefera0le to 0uild low diversion weirs instead of dams! 5 dam will retain thesediment! The diversion weir should 0e euipped with ru00er dams for water retention, and theseshould 0e fully deflated to pass the 0ed load during floods! The intae should 0e placed at rightangles to the flow, and have a low level sluice immediately downstream!

Intake. The intae should have a generous rac area, and provision for automatic cleaning madein regions where there is a large floating de0ris =leafs and twigs> load!

%ondit optimi!ation.5 procedure for conduit optimi/ation has 0een provided! "t is too complex

to summari/e!

Lowpressre pipeline and tnnel. The preferred conduit for transferring water to the penstocis a tunnel! "t reuires the least maintenance! Canals should 0e avoided, they fill with de0riswashed down from the upper slopes! Buried pipes are accepta0le!

Peaking storage. %here the lowpressure tunnel is oversi/ed for the flow, due to minimumconstruction si/e, the tunnel itself can 0e used for peaing storage! 5lso, side tunnel cham0ers

32

Effi$ien$y $omparison

$!:

$!6

$!;

3!$

$!2 $!: $!6 $!; 3!$1low ratio

Effi$ien$y

elton 3 1et!

elton 2 1et!

Turgo

4rancis


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can 0e used for additional storage! Small headponds can sometimes 0e 0uilt in gullies if the localsediment pro0lem is not serious!Srge tank. 5 reuirement for isolated plants! "f the surge tan is omitted in impulsedevelopments, the needle opening time will 0e very long! 5 program for si/ing the tan is providedin the C+-.M!

Pensto$k. 5 0uried pipe is preferred! "f on the surface, spare pipe cans may 0e needed toreplace cans damaged from 0oulders rolling down the mountainside!

Powerhose. "t is prefera0le to locate the powerhouse away from the penstoc cut, to avoiddamage from material dislodged during construction, and after, rolling down the cut! Clean waterfrom the draft tu0es should 0e directed to the next intae downstream, instead of 0eing mixedwith the sandy and siltladen =dirty> water in the headpond!

E4ipment. The preferred layout would have hori/ontal axis units, to facilitate access to thetur0ine runner! "mpulse units =elton or Turgo> are preferred, due to easier replacement of wornparts, in areas where sediment is a pro0lem! 5 program for euipment selection, si/ing andapproximate costing is provided in the C+-.M!

'$knowledgements.

The author thans C5?M(T for the opportunity to mae this presentation, and hopes thatengineers in the audience will find the data useful! Thans are also due to Mr! ! .! S1oman fordata on the +oranTaylor and Soo -iver developments in British Colum0ia, and to Mr! +! 8! T!8ammonds, for data on the Caon del ato development in eru!

#eferen$es.

3! OThe 8arca 8ydro +evelopmentO, Trans (ng! .p! +iv! C(5 )D part 2, 3)*$ paper P*$83$#!

2 O8ydropower (xpansion in Central BoliviaO Trans! (ng! .p! +ivision, C(5 2:, part 2, 3);6!

&! OThe (xpansion of Two Bolivian lantsO, %ater ower and +am Construction, ol! &:, ?o! 2,4e0! 3);2! pp! 26&3!

:! O5ndUalUa Rathering Tu0e 8ydropower "ntaeO 5SC(, Fournal of 8ydraulic (ngineering,ol! 33&, ?o! ;, 5ug! 3);*, pg 3$3)&3!

#! OCaractUristiues de la prise dVeau W 5ndUalUa pur lVexclusion des sUdimentsO, La 8ouilleBlanche, Sept! 3);6! pp! ::3::)!

6! @ower tunnels and penstocsD the economics reexaminedA %ater ower and +amConstruction, ol! &:, ?o!6, Fune! 3);2! pp! 3&3#!

*! @Ena cascada de plantas intercepta at 9ongo en BoliviaA "ngenieria "nternational Construccion ?oviem0re, 3)6;!

; OComparison of "sotatic and 8yperstatic enstocs at Santa "sa0el, BoliviaO, Canadian Fournalof Civil (ngineering, ol! ), ?o! 3, Mar! 3);2, p! 332!

) O8igh 8ead 8ydro owerplant (valuationO proceeding of 5SC(, Fournal of (nergy +iv!, ol!332, ?o! (y&, +ec! 3);6, pp! 3#&36*!

3$! @8ydraulic Tur0ine (fficiencyA, Canadian Four! of Civ! (ng! ol! 2;, P2, 5pril 2$$3! p 2&;#&

3&


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000000000000000000000000000000%omments on some PowerPoint slides.

6. 7ongo storage dam, -oli)ia. 1SL 8 9,:9m.

Constructed in 3)$;, and raised three times, with last raise a0out 3)6#! Located at head of9ongo valley, dam provides seasonal storage for downstream powerplants! The 9ongopowerplant, contains three hori/ontal axis elton tur0ines, operating under &;3m head! Enit P3,installed in 3)$), 3,3$$8! P2, installed 3)&$, 3,3$$8! P&, installed 3):#, :,##$8! Enits areshut down during spring and summer as reservoir is filling with spring flood waters and summermeltwaters from glaciers!

:. Har$a de)elopment ; s$hemati$ profile.

Shows typical features of a high head development! ?ote the followingD- "ntae directly off upstream powerplant tailrace, to avoid entraining siltladen water from river!- Tunnel of minimum si/e, &$< lined with plain concrete, &< lined with reinforced concrete,

2&< lined with steel arches, :< gunnite lined, and :$< unlined!

-Enderground storage cham0ers, usually 0uilt near tunnel adits to facilitate removal of rocand provide air vent!

- Enderground surge tan, 0uilt 1ust off from tunnel to avoid danger of falling roc into tunnel!- alve at top of surface penstoc with automatic closure in case of pipe rupture!

2+. Logs, sand and gra)el in ri)er bed.

5n inspection of the river will indicate the measures necessary to remove de0ris and 0ed load!

2. %hrra4i weir on 7ongo #i)er.

The intae facilities can 0ecome uite complex, and tae up considera0le space! 4rom upstreamto downstream, the drawing showsD-

Low cyclopean concrete weir, with 3'6 upstream slope, 3'3 downstream slope!- Stoplogged intae at right angles to flow, with low level sluice!- Rravel trap with sluice at outlet and weir to spillway!- Side channel spillway with floating 0oom to remove surface de0ris and weir to sand trap!- Sand trap and sluice, weir into canal parallel to powerplant to pic up powerplant flow!%ith all the weirs in the facility, allowance must 0e made for hydraulic losses, which can 0e in theregion of 2 to : meters or more! The weir and intae design is 0ased on the weir downstream ofthe 9ongo powerhouse, for the Boti1laca development 0uilt in 3):$! The Boti1laca weir washed outtwice, 0efore a relia0le design was developed! The Boti1laca weir layout concept has 0een usedon all the 9ongo valley developments!

2:.


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the water surface, to prevent the 0ed load from reaching the trashracs! The gathering tu0eintae is incorporated into the dam, after it was o0served on the model, that the area immediatelyupstream of the dam was always free of sediment! The first alternative included an undergroundsand trap, 0ut this facility proved to 0e inordinately expensive, and was discarded!

*+. %a>on del Pato intake and eroded needles.

There is a 23!#m high dam in the river, with a small low level sluice immediately downstream ofthe intae which is at right angles to the flow! The fore0ay is now completely filled with sediment!There is an underground sand trap, 0ut it is a0out 3'& of the reuired si/e! Conseuently sandand silt flows down the tunnel, entrained in the water! Stainless steel needle cones last a0out 32to 36 days during the flood season! ?ow, ceramic coated needles last a0out &$ to :$ days! Therunners are also eroded! There is a fulltime repair staff for welding runner 0ucets and needles!

5n analysis of the repair costs and the enlargement of the sand trap has found that the repairwor is the most economic alternative!

*. Side hill $anal $aptres melt waters.

5t the head of the 9ongo valley, there are small lateral canals to capture the glacial melt! Thecanals are excavated in roc, are a0out 3m wide, with a masonry side wall a0out $!6#m high!

Slope varies, and is in the region of 3< to $!#

The 8arca slides show the difficulty associated with roc and de0ris from the uphill slope! Thissection of the canal has 0een covered with concrete panels! Some parts of the mountainside areso steep, that undercutting is the only way to o0tain the flow section!

*:. Pingston %reek tnnel.

5t only 2!&m wide 0y 2!&m high, the contractor found the section to 0e too small, and enlargedthe section locally to accommodate the excavating euipment! 5 large portion of the section istaen up 0y the ventilation duct a fact sometimes forgotten 0y designers!

*?. /oran(aylor bried pensto$k.

hoto taen a0out # years after construction! Bury it and forget itX "f the ground is suita0le for a

0uried penstoc, this is the preferred option! "n steep sections, the cover can 0e gravel! The maindifficulty in the steep sections is the pipe support, since this cannot 0e compacted! 5 solution is touse wea concrete slurry, with only sufficient stiffness to remain in place on the slope!

*@. %orani and %hrra4i pensto$ks.

5t 1ust over 3m diameter, the limiting si/e is usually the steel thicness reuired to avoid preheating for welding! The Corani penstoc was 0uilt with an overhead ca0leway! 5 load can 0eseen at top of the slide! The Chururaui slide shows the penstoc traversing a side gully 1ustupstream of the powerhouse! "n steep mountainous terrain, these gullies are a source of roc

3#


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slides and must 0e avoided! ?o structures should 0e located near gullies! 5t this gully, there is aconcrete @si 1umpA to throw roc de0ris over the access road!2. Srge tanks.

"n hilly terrain, the surge tan can 0e located on the hillside, instead of a0ove the penstoc!

=. Har$a powerhose se$tion.

%ith hori/ontal axis units, the powerhouse is simply a sla0 on roc, with a culvert section 0eloweach unit!

9. (rgo rnner.

5 Turgo unit is similar to a elton unit, 0ut the 1et is angled to the runner, and nearer the runneraxis, so that speed is higher! 8ence it can operate at lower heads than a elton unit!

9:. E4ipment sele$tion.

Most manufacturers have selection charts, 0ut none provide details!

0000000000000000000000000000000000000000

-io data for J. L. Gordon.

Mr! Fames =Fim> L! Rordon is an independent hydro consultant with #$ years of experience! 4orthe last 32 years he has provided advice to utilities and consultants on civil and mechanicalaspects of hydro pro1ects! 8e graduated from 50erdeen Eniversity, Scotland, in 3)#2 with a firstclass honors degree in civil engineering! 8e wored for Montreal (ngineering =Monenco> for &;years, retiring as iceresident, 8ydro!

+uring his time with Monenco, he was responsi0le for 6 hydro pro1ects which received awards

from the 5ssociation of Consulting (ngineers of Canada for excellence in design! 8e wasawarded the -icey medal 0y the 5merican Society of Civil (ngineers in 3);) for @outstandingcontri0utions to the advancement of hydroelectric engineeringA and was awarded the Canadian(lectricity 5ssociation +istinguished Service 5ward =3)))> for @his contri0utions to thehydropower industry and the engineering professionA!

8e has authored or coauthored over *# papers on a wide variety of su01ects, ranging fromsu0mergence at intaes to tur0ine cavitation and generator inertia reuirements, and wroteChapter * O4acilities guidelines and case studiesO in 8ydropower (ngineering 8and0oo=McRraw8ill, 3))$>! 8e was part of the scientific team assem0led to produce -(TScreen, anddeveloped the hydro design and cost algorithms used in the program! (S.E-C( +istri0uted(nergy Service of latts, a +ivision of the McRraw8ill Companies, evaluated -(TScreen asOone of the few software tools, and 0y far the 0est, availa0le for evaluating the economics of

renewa0le energy installations!O

8e has 0een an invited speaer at 2$ seminars, and has wored on the design of :6 hydrodevelopments in Canada and overseas, ranging in si/e from 6$$% to #6$M%, and ranging inhead from a few meters, to ;2#m!

8e can 0e reached atD 3$2 Blvd! St!Fean! ointe Claire, ue0ec! Canada! 8)S :93!

(mail 1imgordonYsympatico!ca

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mailto:[email protected]:[email protected]


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Documents

High Head Small Hydro