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Wear 264 (2008) 177–184

Sand erosion of Pelton turbine nozzles and buckets:A case study of Chilime Hydropower Plant

T.R. Bajracharya a,∗, B. Acharya a, C.B. Joshi a, R.P. Saini b, O.G. Dahlhaug c

a Department of Mechanical Engineering, Pulchowk Campus, Institute of Engineering,Tribhuvan University, Lalitpur, Nepal

b Alternate Hydroelectric Centre (AHEC), Indian Institute of Technology, Roorkee, Indiac Norwegian University of Science and Technology (NTNU), Trondheim, Norway

Received 3 March 2006; received in revised form 21 January 2007; accepted 21 February 2007Available online 19 April 2007

bstract

Erosion of hydro turbine components through sand laden river water is one of the biggest problems in the Himalayan region. This problemxists for all kinds of turbines. Apart from erosion of buckets, erosion was also observed in nozzle of the Pelton turbines due to sand particles anduch problem was observed in 22 MW Chilime Hydropower Plant in Nepal. Detailed studies were conducted and erosion analysis was carried outn this case study. Sieve and mineral content analyses were systematically carried out and sediment load was calculated. By doing this, erosion

ate and efficiency reduction were established using already known methodology and scenario for similar hydropower plants. The flow analysishrough surface of needle was established by drawing flow net diagrams. This detrimental damage led to efficiency reduction of 1.21% consequentlyesulting in loss of power generation. A wear rate of 3.4 mm/year was estimated for the needle and the bucket after a systematic analysis.

2007 Elsevier B.V. All rights reserved.

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eywords: Erosion; Sand particles; Bucket; Nozzle

. Introduction

Water resource in Nepal is one of the major energy resourcesnd in fact is a gift of the nature. This is formed by the snow-apped mountains, glaciers and regular monsoons. An averagennual precipitation of 1503 mm and an annual runoff of about24 billion cubic meters through more than 6000 large and smallivers have largely made Nepal rich in hydropower with itsotential of about 83,000 MW. Presently, only 43,000 MW isechno-economically feasible to tap [1]. However, till date, onlyround 600 MW has been harnessed.

The influence of heavy rains during the monsoon periodJune–September) causes wide variation in river flows, land ero-ion and landslides in Nepal. This produces high sediment in the

ivers due to the fragile geographical composition of the coun-ry. Sediments are formed due to the fragmentation of rock dueo chemical and mechanical weathering. The sediments in river

∗ Corresponding author. Tel.: +977 1 5542054; fax: +977 1 5525830.E-mail address: triratna@ioe.edu.np (T.R. Bajracharya).

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043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.wear.2007.02.021

ater are mixtures of particles with different sizes as presentedn Table 1.

It is estimated that the total specific sediment yield of theountry is about 4240 tonnes/km2/year. Marshyangdi River isne of the sediment-laden rivers in Nepal [2]. The sedimen-ological study performed in 1981 has revealed an averagennual load of 26.7 million tonnes and bed load of 2.9 mil-ion tonnes. Out of this total load, 90% of the sediments areransported in the river during the monsoon season from Mayo October. Similar conditions also prevail in rest of the rivers.uch excessive sediment in the Himalayan Rivers is also due

o the presence of weak rocks, and extreme relief in the regionpart from heavy monsoon. Hence sediment management hasecome primary importance for the safety, reliability and longerife of infrastructure projects like hydropower, irrigation andrinking water projects in Nepal. The sediment data collec-ion was started in Nepal since 1963 in Karnali River basin.

ydropower projects like Marsyangdi, Jhinuuk and Khimti areonitoring sediment transport phenomenon regularly. Still there

s a lack of sufficient information of sediment quantity androperty for scientific analysis to investigate its detrimental

178 T.R. Bajracharya et al. / Wear 264 (2008) 177–184

Table 1Classification of river sediment

P San

S 0.06

eo

hTgraFod

2

coaaptCo

tcSafitpt11

pioRdpicppwp

aaaTls

3

iabcvstns

article Clay Silt

ize (mm) Less than 0.002 0.002–0.06

ffects [3]. Fig. 1 shows quartz content in some of the riversf Nepal.

The particles causing erosion of turbine components inydropower plants are the sediments contained in river water.hese sediments are found in a form of clay, silt, sand andravel with the specific gravity of approximately 2.6. In theiver hydraulics, sediment particles are classified into bed-loadnd suspended-load based on transport mechanism of sediment.raction of suspended load is settled down in the settling basinsr reservoirs and rest will pass through turbines causing wear ofifferent components.

. Chilime Hydro Electric Project (CHEP)

There are 19 hydropower plants in Nepal with generatingapacity of 2 MW and more. Mostly these projects are Run-ff-River (ROR) except Kulekhani Hydropower plant and areffected by sand erosion. Such kind of erosion has become

part of the regular activities in most of the hydropowerrojects. Under the present study, an analysis for sand par-icle led damages of Pelton needle has been carried out forhilime Hydropower Plant (CHEP) having total plant capacityf 22 MW.

The CHEP is a ROR type project with 4 h peak load. It takeshe water from the Chilime River which then flows from theanal into the desilting basin where the sediments settles down.ubsequently, the water flows through the siphon into the cutnd cover canal and then into the by-pass canal and into theore bay. Then the water through the headrace channel flowsnto the penstock and enters in to the nozzle of the turbine. Theurbine is coupled with the generator and thus the electricity is

roduced. The water after striking the turbine flows through theailrace channel back into the river. The head works consist of1 m long simple weir, 4 m wide under sluice, and 4 m wide and.6 m high two numbers of intake gates to divert the water to the

Fig. 1. Average quartz content in the rivers of Nepal.

fursofla

4

E

br

E

d Gravel Cobbles Boulders

–2 2–60 60–250 Greater than 250

ower canal through 45 m long gravel trap. An overflow spillways provided at the end of the gravel trap. Desilting basin is locatedn the flat terrace field between Chilime River and the Bengdangiver providing sufficient flushing head. Desilting basin is 315 mownstream from the gravel trap end. A cut and covered canal isrovided in between the gravel trap and the desilting basin. Annverted siphon is provided to flush Bengdang River. A cut andover canal is provided in between siphon end and the peakingondage has a capacity of 44,160 m3 which is sufficient for 4 heaking time. Two 11 MW units of double jet Pelton turbinesere installed in this plant. The river supplying water for thislant is fed by snowmelt in Himalayas [4].

The main source of fine sediments is from the process of sheetnd reel erosion. The glaciers produce some bed load sedimentsnd are left as end moraines. Land slides and mass wasting arelso the main sources of suspended and bed load sediments.hose events produce very high sediments load and the bed-

oad materials are deposited along the bed and produce highediment concentration during the subsequent years.

. Methodology

Secondary and primary data were collected by personal vis-ts of the CHEP plant site by the study team. Sample of sandnd water, which were taken from the Chilime River, wererought to the laboratory and sieve and mineral analyses werearried out. Staff members and technical personnel were inter-iewed to find out the possible causes of erosion of needle andeat rings. Data pertaining to erosion observation during main-enance and second maintenance were collected. Then erodedeedle and seat rings were bought to the laboratory and wear andurface texture were studied by measuring wear depth and sur-ace roughness using stylus probe. Sediment load was calculatedsing standard relation. By doing this wear rate and efficiencyeduction were established using already known method andcenario for similar hydropower plants. Then analysis of flowf water through surface of needle was carried out by drawingow net diagrams. Based on the observations, measurementsnd analysis, conclusions were drawn.

. Models of erosion

The most often quoted expression for erosion [5] is:

rosion ∝ (Velocity)n. (1)

There are several other fundamental studies of erosionehavior and its prediction. General erosion model given by

esearchers is as follows:

rosion = f (operating conditions, properties of particles,

properties of base material) (2)

/ Wea

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W

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T.R. Bajracharya et al.

Generally, this expression is given as a function of velocity,aterial hardness, particle size, and concentration. The most

eneral relation for erosion purpose [3,6,7] is:

= KmatKenvcVnf (α) (3)

ere, W is the erosion rate (material removal) in mm/year, Kmathe material constant, Kenv a constant depending on environment,the concentration of particles, f(α) a function of impingementngle α, V the velocity of particles and n is the exponent ofelocity.

The erosion models are basically developed for specificurpose or condition. Truscott [5] presented the equation ofergeron to predict the erosion rate of pump with simplifiedssumptions such as pure sliding of spherical particles over theurface. He presented equation for erosion as:

rosion ∝ V 2

D(ρp − ρ)d3pK (4)

here V is the characteristic velocity of liquid, D the character-stic dimension of the machine, ρp the density of particle, d theiameter of particle, p the number of particles per unit surfacerea, ρ the density of liquid and K is the experimental coeffi-ient depending upon nature of abrasive particles. This equations proportional to experimental coefficient, which is dependentn abrasive nature of particles.

Karelin et al. [8] established the equation for surface erosionased on impact effect of particles considering kinetic energy ofingle particle. They have anticipated deviation on erosion esti-ated by equation due to uncertainties like non-homogeneous

articles, variable concentration, continuous alteration and pul-ation of velocities and pressure, non-uniform flow distributionnd so on. On the contrary to laboratory tests, Tsuguo [9] estab-ished the relationship of factors concerning erosion of turbinesased on 8 years erosion data of 18 hydropower plants. Theepair cycle of turbine is determined according to calculation of

urbine erosion from equation, which gives erosion rate in termf loss of thickness per unit time (W):

= βcxayk1k2k3Vn (5)

0wtc

Fig. 2. Particle size

r 264 (2008) 177–184 179

here β is the turbine coefficient at eroded part, c the concen-ration of suspended sediment and V is the relative velocity.he term a is average grain size coefficient on the basis of unitalue for grain size 0.05 mm. The terms k1 and k2 are the shapend hardness coefficient of sand particles and k3 is the abrasionesistant coefficient of material. The x, y and n are exponent val-es for concentration, size coefficient and velocity, respectively.he value of x and y are close to the unity and any deviationf this linear proportionality is determined from plot of wearersus parameter. The values of n are proposed for differenturbine components based on relation between relative velocitynd erosion. Minimum value of n is proposed as 1.5 for Peltonucket and maximum value is 3 for Francis turbine runner. Sim-larly, for Francis turbine guide vanes and Pelton turbine needle,his value is proposed as 2.5. The equation similar to this forhe purpose of hydraulic turbines has been established in thistudy.

. Analysis

.1. Sediment analysis

The analysis of water samples collected on different daysrom the settling basin area showed a maximum sediment con-entration of 2037 ppm with the sand break of 79% (which is9% of total sediment is sand). The particle size distributionnalysis was done by sieve analysis method and visual accu-ulation tube (VAT) method. The results of sieve analyses are

resented in Fig. 2.It can be seen from Fig. 2 in VAT method that only 5% of the

otal sediment has the particle size less than 60 �m and 99% ofhe sediment has the particle size less than 4500 �m.

Fig. 2 in sieve method shows that only 5% of the sedimentample has the size less than 62.5 �m and the whole sedi-ent samples have the size less than 1000 �m. The settling

asin is designed to trap the sediment particle of size up to

.2 mm (200 �m). From the particle size distribution analysis, itas found that around 35–40% of the sediment has the par-

icle size less than 200 �m. This indicates that during floodondition, when the river carries large amount of sediment,

distribution.

180 T.R. Bajracharya et al. / Wear 264 (2008) 177–184

Table 2Distribution of sediment samples

Minerals Percentages (%) by volume Mohr’s Hardness Scale Remarks

<1 mm <1 mm <1 mm Average (%)

Quartz 75 76 77 76 7 Mica content is highFeldspar 7 6 6 6 6 Other minerals mainly content garnet, tourmaline and rock fragmentsMBO

3iec7cc

eo2ic

5

puiptehii

5

uadIne

m

TE

R

ABCD

Even though the settling basin with Sediment Sluicing Ser-pent System (S4) is performing according to design criteria,large quantity of sediment (may be particles smaller thandesign size) pass through turbines especially during mon-

uscovite 5 6 5 15 2–3iotite 10 9 9thers 3 3 3 3 >6

5–40% of sediment will reach up to the turbine, thus caus-ng severe erosion of the turbine components. As mentionedarlier, the maximum concentration recorded during the floodondition to be 2037 ppm. A 35–40% of this value equals to13–815 ppm, which is very high as compared to the total con-entration obtained for the samples taken in other normal flowonditions.

In year 2006, sediment deposition volume in the reservoir wasstimated. On July 10, 2006, the estimated volume was 387 m3,n August 14, 2006, it was 10018.81 m3 and on October 15,006, it was 2732.72 m3. The maximum sediment was depositedn flood time. This is clearly indicated that only desilting basinannot control sediments.

.2. Mineral content analysis

The mineral content analysis was carried out to determine theercentage by volume of the minerals in the water being carriedp to the turbine. It was found that the average quartz contents 76% and feldspar is 6%, amounting to a total of 82%. Thearticles are angular to the sub rounded shape. This indicateshat the river water with sand has the high probability for therosion of the turbine components. This is due to the very highardness of quartz and feldspar, which is 7 and 6, respectively,n Mohr’s Hardness Scale. The distribution of sediment sampless present in Table 2.

.3. Erosion observation

In July 2004, the first maintenance of the power plant wasndertaken. During this period, erosion between the nozzle tipnd the spur needle was observed. Table 3 and Fig. 3 provideetails of erosion and its location in the needle and nozzle tip.t clearly shows the erosion thickness (gap) between the spur

eedle and the nozzle tip. At the same time, it also depicts therosion at the tip of the spur needle.

The erosion of turbines due to sand content in water is com-on in Nepal and therefore some of them are presented below.

able 3rosion on the needle tip

egion Unit 1 (mm) Unit 2 (mm)

–B 0.30 0.10–C 0.48 0.05–D 0.31 0.40–A 0.10 0.30

(a) Khimti-1 Hydropower PlantThe 5 × I2 MW Khimti-1 Hydropower Plant (KHP-1)

installed in 684 m gross head represents typical high headpower plants in Himalayan Rivers. The horizontal Peltonturbines of KHP-I have two jets with discharge 2.15 m3/s.Khimti River of KHP is also example of rivers with highgradient, heavy monsoon flow and high sediment concen-tration of hard minerals. Less than 20% of Khimti Basinlies in High Himalayas, about 30% in Lesser Himalayas and50% in the region of middle mountains, which is formed asa result of local tectonic movements, river down cutting andsedimentation. Hence the risk of rock falls and landslidesare high and extensive deforestation has led to increased soilerosion. The average concentration of suspended sedimentat Khimti River in 1994–1995 monsoon seasons varied from13 to 1244 ppm and maximum-recorded concentration was8536 ppm [10]. The higher concentration is expected in theflood situation and hence 20,000 ppm suspended sedimentis used as design value for sediment settling and flushingcapacity. Two parallel sediment settling basins which wereoptimized with respect to erosion of turbine are dimensionedas 90 m × 12 m × 2 m to exclude 85% of all particles witha fall diameter of 0.13 mm and 95% of all particles with afall diameter 0.20 mm [11].

Significant amount of erosion had appeared in turbinebucket and needles in first year of operation (about 6000 h).

Fig. 3. Spur needle and nozzle tip erosion.

/ Wear 264 (2008) 177–184 181

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T.R. Bajracharya et al.

soon. Since this is a high head turbine, even 0.15 mm particlehave high particle impact energy approximately 8.12 �J thatcause severe erosion of turbine components [3]. The runnerof this turbine is made up of steel 13Cr4Ni. The thicknessof bucket close to the root is found 11 mm; whereas thethickness around centre and entrance lip is 12 mm. Henceit appears at least 1 min thickness is already lost towardsroot. From the strength point of view, the thickness towardsto the root should have been more. Runner outer diameteris 800 mm with 22 buckets. Distinct erosion is observed inthe area towards root and outlet region of the bucket. Butthe area on both sides of splitter is smooth and appears as ifthere is no erosion.

Both the nozzles and needles of KHP are eroded. Theinner side of nozzle tip have also pattern similar to themiddle section of the needle. This ripple pattern is typi-cal in the needle with the circular grooves when viewed inaxial direction. Two distinct grooves towards axial directioncan be observed straight ahead of the two webs to supportneedle guide. This could be due to vortex formed at thetrailing edge of such webs. These groves are approximately70 mm length starting from the needle tip and are nearly10 mm wide. Out of the 150 mm taper length, nearly 70 mmfrom tip is affected with relatively higher ripple wavelengthexcept at tip. The last 30 mm toward the bottom of taper issmooth and polished and the remaining portion with finescales.

b) Kulekhani-I Hydropower StationKulekhani-I is a reservoir type hydropower plant

designed as a peaking power plant with the 60 MW installedcapacity. It annual generation capacity is 211 GWh. Thecommercial date of operation is 1982.

It consists of two set of Pelton turbine with the ratedcapacity of 30 MW each. The net head is 550 m andthe design discharge is 13.1 m3/s. The generator is thevertical shaft, synchronous generator with the capacity

of 35 MVA.

Major problem seen in this hydropower plant since itgeneration had started is: in 1993, the unprecedented floodcaused a major damage to the penstock and an unexpected

s

tu

Fig. 4. Erosion profiles of needle: (a) severely erod

Fig. 5. Bucket erosion.

inflow of 52 million m3 of water with huge silt was observed.This caused the filling of the bed level of the reservoir byabout 6 m in 1 year with the total deposition of silt to the tun-nel of 23 million m3 in 21 years. To overcome this problem,slopping intake was constructed that raise the inlet waterlevel from 1476 to 1480 m, reducing the overall capacity ofthe line pondage from 73.2 to 62.3 m3, causing a reductionin the generation capacity also. Since then, the powerhouseis running quite satisfactorily.

.3.1. Second maintenance periodEleven days after the first maintenance period, the second

aintenance was taken up. During latter maintenance period,evere erosion was observed both in the spur needle and theucket. The measurement of erosion was taken up and the pro-le of the erosion surface was developed. Fig. 4 shows therosion profile for the spur needle of lower and upper nozzles,espectively.

The nature of erosion is found to be quite unusual. Thereas a groove along the radially opposite part of the conical

pur needle, which was also noticed by other investigators asell. The remaining part has the usual mode of erosion. Theotted line in the figure shows the actual profile of the spureedle, while the profile in the continuous line shows the eroded

urface.

Fig. 5 shows the erosion of bucket. It was found that half ofhe bucket was more eroded than the other half, which is quitenusual.

ed surface and (b) uniformly eroded surface.

1 / Wear 264 (2008) 177–184

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82 T.R. Bajracharya et al.

.4. Sediment load and prediction of erosion

Sediment load calculation was carried out to determine thepproximate amount of sediment, which cannot be trapped andeaches up to turbine. It is calculated from the following equa-ion:

SLt = Qt(T2 − T1)

⌈(C1 + C2)

2

⌉60 × 60 × 10−6 (6)

here SSLt is the suspended sediment load to the turbinetonnes], Qt the discharge to the turbine [m3/s], C1 the concentra-ion in the flow to turbine at time T1 [ppm], C2 the concentrationn the flow to turbine at time T2 [ppm], T1 the duration of lastbservation [h] and T2 is the duration of consecutive observationfter time T1 [h].

It is obvious from the equation that erosion rate increasesith the sediment load. Its value indicates the amount of

ediment between two sample periods. The amount of sedi-ent that reaches to the turbine during the 11 days period is

0,805.35 tonnes, which is very high.

.4.1. Erosion rate and efficiency reductionErosion rate is also a function of the particle size. The coarse

ize particles cause more erosion compared to fine size particles.owever, finer size particles with higher quartz content will haveigher potential for the erosion.

Fig. 6 shows the effect of particle size on erosion rate atifferent quartz content levels. It is clear that for the same particleize, the erosion rate increases with the increase in the quartzontent. Also, for given quartz content, the erosion rate increasesith the increase in the particle size.The relationships between the erosion rate and the particle

ize at different quartz content levels are as follows:

rosion rate ∝ a(size)b (7)

For quartz content of 38%, a = 351.35, b = 1.4976;For quartz content of 60%, a = 1199.8, b = 1.8025;

For quartz content of 80%, a = 1482.1, b = 1.8125.

As for the CHEP, the mean size of the particles reaching upo the turbine is 0.035 mm and the quartz content as shown by

Fig. 6. Effect of particle size (and quartz content) on erosion rate.

patt

5

5

wtpi

diotg

Fig. 7. Effect of erosion on efficiency of turbine.

ineralogical analysis, is nearly about 80%, giving the erosionate 3.4 mm/year. The cumulative erosion will amount to around.8 mm in 2 years of operation. From the measurement, the max-mum erosion of the needle surface was found to be 7.1 mm,hich is close to the result obtained from the calculations.With the increasing erosion of the surface, friction will also

ncrease. As a result, the flow will be turbulent and the erosionate will be enhanced. This ultimately will result in the reductionf the efficiency of the turbine as shown in Fig. 7.

The relation between the erosion rate and the reduction effi-iency is given by:

fficiency reduction ∝ a(Erosion rate)b (8)

here a = 0.1522 and b = 1.6946.For CHEP, with the erosion rate of 3.4 mm per year, the reduc-

ion in the efficiency of the turbine will be 1.21% for the firstear of operation and around 4% in the next year if it is continu-usly operated without maintenance. Such kind of phenomenonan have adverse effect on the power generation.

Generally, power losses and efficiencies within a hydropowerystem is calculated as [12]:

= ηpenstock × ηmanifold × ηturbine × ηdrive × ηgenerator (9)

When sand or silt laden flows exist, the overall reductionn efficiency is due to several attributes and components of theower plant, which all contribute to overall efficiency reductionnd power loss. However, in this study, efficiency reduction (ofurbine) have been calculated only on the basis of ηturbine andherefore the reduction of turbine efficiency is considered.

.5. Erosion behavior on needle

.5.1. Flow net for full opening of needleThe flow net for the full opening condition of the nozzle along

ith the needle was drawn and the variation of the pressure andhe force along the surface of the needle was calculated andresented (Fig. 8) (flow net diagram for fully open needle valves shown as an inset).

It is further observed that the force along the surface of needleecreases. But at the same time, the mean velocity of the flow

ncreases due to gradual contraction in the fluid passage. Basedn these data, the relation between the force along the surface ofhe needle and the mean velocity can be developed by plotting araph with reference to the distance along the surface of needle

T.R. Bajracharya et al. / Wear 264 (2008) 177–184 183

Fo

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ig. 8. Variation of force and mean velocity along the surface of needle (fullpening condition).

please see inset in Fig. 8). From the figure, it becomes clear thatecause of the relatively low mean velocity, the erosion on theeedle surface at the beginning is low though the force on it iselatively large. At the subsequent stage, because of the increasen the flow velocity, erosion of the surface will be higher thoughhe force on the needle decreases. Since the dominant factoror the erosion is the velocity [Erosion ∝ (Velocity)3] and ashe cross-sectional area is gradually reduced, the increased flowelocity might cause the turbulence in the flow thus enhancinghe erosion of the surface. But at a latter stage, because of theery low force on the surface of the needle and the fact that theet flows freely under the atmospheric pressure, the erosion ofhe surface near the tip of the needle due to the sediment is noto severe though the velocity of the flow is relatively very high.s the needle is very sharp at the tip, even the small force at aery high velocity can erode the tip easily.

.5.2. Flow net for half opening of needleThe flow net for the half open condition of the needle and the

ozzle has been drawn in the same way as it was done for theull opening condition. Also force and the mean velocity of flowave been calculated in the similar manner. The result obtainedas quite different in this case. Fig. 9 presents force and meanelocity as a function of distance along surface of needle underalf open condition (flow net is shown as an inset). The pressure

long the surface of the needle decreases as in the case of fullpening. But at a later stage its value becomes negative indi-ating the occurrence of cavitations possibility due to increasedurbulence in the flow. Both the force along the surface of the

ig. 9. Variation of force and mean velocity along the surface of needle (halfpening condition).

•

•

o

•

•

ig. 10. Severely eroded surface of turbine needle due to inception of cavitation.

eedle and the mean velocity of the flow continuously increases.hus, the combined effect of the cavitations and the sedimentrosion gives rise to the severe erosion of the needle surface.ig. 10 shows highly eroded surface of needle due to cavitation.

The damage of the needle surface increases with turbineunning time under partial flow conditions due mainly to theccurrence of cavitation. In case of full opening condition, thiss not observed.

. Conclusions

As erosion caused by sand and or silt-laden flows for variousomponents of hydro turbines is commonplace in Himalayanegion, the importance of sediment transport and natural pro-esses should not be underestimated. Specifically for case ofHEP, following conclusions are drawn:

The quartz content of the Chilime River is relatively high. Dur-ing the monsoon period, large amount of sediments reach theturbine buckets and needle. High quartz content and increasesediment load during monsoon along with the small particlesize are the major cause for the severe erosion of turbine parts,namely the nozzle and buckets.The erosion rate of 3.4 mm/year for the needle and the bucketresulting in efficiency reduction of 1.21% and as a conse-quence loss in the power generation.The longer the needle is operated in partial (half) openingcondition the greater is the erosion of the needle due to theadditional effect of cavitations along with sand erosion. As aresult, high turbulence occurs in the flow, jet miss and thus thebucket resulting ultimately affecting the turbine performance.

Suggestions for reduction of sand/silt and increasing the lifef turbine components have been given as follows:

Provision of series of low head weirs in the river courseupstream of hydropower plant.Provision of trench weir.

1 / Wea

••

R

[

[Himalayan rivers: case study of Khimti I hydropower project Nepal, in:

84 T.R. Bajracharya et al.

Proposing diversion tunnels.Regular desilting (by dredging and or siphoning, reservoirflushing through bottom outlets, etc.) and maintenance of stor-age reservoir, etc. The decision however has to be taken afterfully evaluating the cost for the replacement of spares versuscapital cost for extra structures.

eferences

[1] Centre for Energy Studies, Renewable Energy Perspective Plan of Nepal2000–2020, Micro Hydro Sectoral Report, Tribhuvan University, Instituteof Engineering, Kathmandu, Nepal, 2000.

[2] C.S. Chaudhary, Impact of high sediment on hydraulic equipment ofMarsyangdi hydropower plant, in: Proceedings of the International Seminaron Sediment Handling Technique, NHA, Kathmandu, 1999.

[3] B. Thapa, Sand Erosion in Hydraulic Machinery, Ph.D. Thesis, Norwegian

University of Science and Technology (NTNU), 2004, pp. 9–28.

[4] B. Acharya, B. Karki, L. Lohia, Sand Erosion Led Damages of PeltonTurbine Components and its Effects, BE Thesis, Department of Mechan-ical Engineering, Pulchowk Campus, Institute of Engineering, TribhuvanUniversity, Nepal, 2005.

[

r 264 (2008) 177–184

[5] G.F. Truscott, Literature survey of abrasive wear in hydraulic machinery,Wear 20 (1972) 29–50.

[6] E. Bardal, Korrosjon og Korrosjonsvern, Tapir, Trondheim (in Norwegian),1985.

[7] B.K.S. Naidu, Silt erosion problem in hydropower stations and their pos-sible solutions, in: Proceedings of the Silt Damages to Equipment inHydropower Stations and Remedial Measures, New Delhi, 1996, pp. 1–53.

[8] V.Y. Karelin, et al., Fundamental of hydroabrasive erosion theory, in: C.G.Duan, V.Y. Karelin (Eds.), Abrasive Erosion and Corrosion of HydraulicMachinery, Imperial Press College, London, 2002, pp. 1–52.

[9] N. Tsuguo, Estimation of repair cycle of turbine due to abrasion caused bysuspended sand and determination of desilting basin capacity, in: Proceed-ings of the International Seminar on Sediment Handling Technique, NHA,Kathmandu, 1999.

10] K. Haakon, Khimti-I hydropower project, in: Proceedings of the OptimumUse of Run-off-River Conference, Trondheim, 1999.

11] M.B. Bishwakarma, G.P. Dhakal, P. Pradhan, Headworks design in

International Conference Hydro 2003, Crotial, 2003.12] J. Thake, The Micro-Hydro Pelton Turbine Manual: Design, Manufacture

and Installation for Small Scale Hydropower, ITDG Publishing, London,2000.