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Review on erosion phenomenon, maintenance,
and financial calculation of lifetime as an asset for
Pelton turbines
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et al
2023
J. Phys.: Conf. Ser.
2629 012008
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Current Research in Hydropower Technologies 2023 (CRHT-XI)
Journal of Physics: Conference Series 2629 (2023) 012008
IOP Publishing
doi:10.1088/1742-6596/2629/1/012008
1
Review on erosion phenomenon, maintenance, and financial
calculation of lifetime as an asset for Pelton turbines
Jim Abregu1*, Nirmal Acharya1, Bjørn W. Solemslie1,2
1Waterpower Laboratory, Department of Energy & Process Engineering, Norwegian
University of Science and Technology, NO-7491, Trondheim, Norway
2Department of Aquatic Biodiversity, Norwegian Institute for Nature Research, NO-
7485, Trondheim, Norway
* Corresponding author (jim.abregu@ntnu.no)
Abstract. Prevention of greenhouse emissions is the top priority for all countries, which
urges them to switch to renewable energy as much as possible. Hydropower is one of
the renewables that have high flexibility and at the same time compatibility to be used
with any other renewable sources. Moreover, hydropower plants operating in the
Himalayas, Andes, and Alps are facing operational challenges due to the high
concentration of sediment loads in rivers. Although the arrangement of traditional
sediment control mechanisms like dams and sand traps, the erosion tendency of hydro-
turbine components operating in this sediment-laden water increases with the increased
concentration of sediments. Much past research has been directed towards
understanding sediment behaviors, investigation of flow, and effect of concentration,
shape, and size, especially with Francis turbines. However, there are very fewer studies
regarding sediment erosion and flow behavior in the case of the Pelton turbine. Hence,
delving deeper into the flow characteristics, sediment behavior, and performance of the
Pelton turbine is important to better understand the flow and sediment pattern of these
types of turbines. The paper consists of the evaluation of studies conducted on the flow
pattern in the Pelton turbine buckets and its validation with the numerical analysis
models using image processing. It is being used in the Waterpower Laboratory at the
Norwegian University of Science and Technology, NTNU. This paper also evaluates
the scope of investigations about erosion by sediments in Pelton buckets using image
analysis and state-of-the-art technology in the hydropower sector. In addition, a review
is done about the predictability of erosion based on the measurements of the quantity
of sediments that passes through the turbine. This research paper can build a
background for quantifying sediment erosion in Pelton turbines with a certain degree
of error, which can be utilized as a reference in future studies. The life cycle estimation
of a turbine is also analyzed with the consideration of its location and financial return
requirements together with the type of maintenance that it may have and the repair that
is foreseen, in the case of a non-coated surface.
Keywords: Erosion, Flow behavior, Image analysis, Pelton turbine, Sediment particles.
Current Research in Hydropower Technologies 2023 (CRHT-XI)
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doi:10.1088/1742-6596/2629/1/012008
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1. Introduction
Hydroelectric power is one of the flexible renewable sources and is supposed to contribute the most to
slowing down the pace of climate change [1]. Hydropower plants operating in sediment-laden water are
facing severe operational challenges due to higher sediment loads resulting from irregular rainfall
intensities caused by global warming. The erratic rainfall intensity increases the sediment loads by about
1.6% for every 1% change in rainfall although sediment-decreasing factors like agriculture and the
construction of big dams are considered [2].
The feasible areas of the rivers for hydropower projects are shown in Figure 1 along with the rivers
which are excessively used for irrigation, water consumption, fragmentation, and regulation. It can be
seen that the feasibility of building a new hydropower project seems possible in rivers that originated
from young mountain ranges such as the Andes and the Himalayas. These rivers are facing challenges
of high sediment loads which are increasing each year due to changes in rain patterns and the melting
of glaciers [3, 4]. The effects of such a higher concentration of sediment in this river have been reflected
in the severe wear and tear of hydro turbines operating in these regions. This wear and tear increase the
maintenance costs and decrease hydropower generation, which is increasing each year.
Figure 1. Map of rivers without alterations in their path (modified from Grill 2019).
Dams, and sand traps at the intakes and inside the tunnels, are used for the retention of the sediments to
reduce their passage through the turbines. The effectiveness of these infrastructures in controlling
sediments is calculated with different methods and depends on various hydraulic and hydrological
factors apart from the sediment properties [5].
Due to their impact on river biodiversity, nutrient transport, and spawning habitat disturbances, dams
are facing increased regulation by environmental agencies [6, 7]. Currently, new dam designs are
evaluated considering the management of sediment loads, minimizing their impact on the environment,
and respecting the transit of fish, which are under ecological standards being implemented [8]. The
capacity of dams around the world is decreasing by about 1% annually [8, 9]. All these considerations
related to sediment handling directly impact the turbine. It is important to plan the overhauling of a
turbine according to the sediment loads, peak power demand, availability of resources, and the severity
of erosion on the components.
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doi:10.1088/1742-6596/2629/1/012008
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This paper briefly reviews the research on sediment erosion, repair, maintenance, and useful lifetime
for a Pelton turbine. First, an overview of sediment management and facilities of the hydroelectric
power plant during the transportation of the sediments is discussed with its close connection with
erosion in the Pelton turbine. Further, the erosion and the field investigation of erosion are discussed.
Moreover, aspects directly related to the turbine, especially the flow of water and sediment through the
turbine, are also evaluated. The financial part of a hydroelectric project includes the turbine as an asset
subject to return-on-investment evaluations. To consider the complete evaluation of the life of a turbine,
the types of maintenance that are practiced and their implication in the useful life of the turbine are
analyzed. Finally, the useful life of a Pelton turbine is discussed, along with the author’s perspective.
2. Erosion on Pelton turbines
There are many studies on the mechanics of how sediment induces erosion on turbines [10, 11]. The
erosion in Pelton turbines is a peculiar phenomenon that combines several factors [12]. The
predictability of how long a Pelton turbine can be operated continuously without maintenance is still a
topic in development. IEC 62364 [13] had made good advancements in studying erosion behavior and
gave a guideline for the prediction of erosion. However, there are some conditions where erosion occurs
on all the surfaces of wet components of the turbine exponentially [14]. Figure 2 shows the irregular
behavior of the erosion at different wetted surfaces of the Pelton turbine.
Figure 2. Cavitation on Pelton turbines. a & b) Cavitation on the inner surface of the bucket and break
of a side of the outlet edge at Ancash-Peru. c) Cavitation on the inner surface, Smith [15]. d) Cavitation
in the bucket splitter at Lima-Peru. e) Cavitation on the inner surface and lips of the bucket at Pasco-
Peru. f) Cavitation on the inner surface of the bucket at Pasco-Peru.
(a)
(b)
(c)
(d)
(e)
(f)
Current Research in Hydropower Technologies 2023 (CRHT-XI)
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When the erosion starts creating wave patterns on the surface it can be considered the beginning of
cavitation [10] which can be observed in Figure 3. This type of pattern is also observed in the splitter
where it loses material and will remain as a blunt-lateral surface for the jet of the water as the erosion
advances [10].
Figure 3. Regular erosion with starting of cavitation in Pelton turbine buckets. a) Runner after one year
of operation at Pasco, Peru. b & c) Runner after four months of the rainy season at Ancash, Peru.
The combination of steady erosion and cavitation results in aggressive material loss, and irregularities
in the wetted surfaces, and ultimately put the integrity of the Pelton runners at risk. These types of
combinations can be seen in Figure 4 which can occur due to defects in the turbine, manufacturing as
well as repairing process, and/or poor maintenance management.
Figure 4. Aggressive erosion is caused by a combination of effects. a & b) welding reparation defect
with erosion on the inner surface at Chiclayo Peru. c & d) Cavitation on the outlet edge at Ancash, Peru.
(a)
(b)
(c)
(a)
(b)
(d)
(c)
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2.1. State-of-the-art research on Pelton turbine
One of the reasons Pelton turbines are selected for many hydropower projects in the overlap region is
due to low vibration as compared to Francis turbines [16]. In addition, Pelton turbines have easiness of
using the deflectors to prevent water hammer with sudden cuts in the water flow, and also facilitate
maintenance inspections as it does not require the draining of the turbine chamber [18].
Since the first Pelton turbine came into operation in 1878 at the Mayflower Mine in Nevada City [19],
its design and material have been improving and currently, almost 92% efficiency can be achieved on
an industrial scale. In addition, it can work in a larger range with high efficiency and reduced cavitation
damage compared to the Francis turbine [20]. The studies on the design and improvement of Pelton
have been increasing in recent years due to independent academic work with industrial support [21, 22].
However, some complications make the research and development work of the Pelton turbine not at the
same level as other hydraulic turbines. The flow regime that governs the water is classified by the
dimensionless Reynolds number (Re), then after leaving the injector the water jet is governed by the
Weber number (We) and finally, the interaction between the water and the rotating runner is handled
under the regime of Froude number (Fr) [22].
The improvement in the efficiency of the flow of water inside the manifold has also been an area of
research and numerical tools have been extensively used in recent years. Figure 5 shows that the design
of the manifold is also important as bad design can account for an efficiency loss of 2-3% [23]. In
addition, the efficiency drop can be increased up to a 2% increase in the nozzle due to the improvement
in instability phenomena [24]. Although some interference might occur in the jets while working with
6 injectors and high specific speed [18], the deficiencies in the opening sequence of injectors have also
been evaluated in ramp-up and ramp-down with their implications for vibrations and the need for
hysteresis between operations to avoid repeated switching of the injector. But, there are also
implications for the fatigue suffered by the turbine due to irregular loads [25]. Once the water leaves
the injector, the losses in the jet can account for an overall decrease in turbine efficiency by 1.5% [26].
The losses in the jet are dependent on several factors, such as the distance between the injector and the
bucket. For instance, the increase in the distance between the injector and the bucket more than four
times the diameter of the jet generates a deformation of 1 mm in the axis of the jet [27].
Figure 5. Inlet turbulence intensities in the Pelton manifold, modified from [23]
The use of tools like FEM and CFD during the design phase of the Pelton turbine enables to increase
of the overall efficiency up to a significant level [28]. At the same time, the desire for higher efficiency
demands the structures to be thinner forcing the limit of resistance to mechanical stress. High stress
combined with the increasing starts and stops results in more turbine failures, and it has been increasing
due to the popularity of hybridization of hydro energy to other renewable energy sources such as wind
and solar energy. Stress loading due to repetitive cyclical loading can cause small cracks that are not
easy to detect and over time can propagate suddenly leading to overall bucket failure [25].
Turbine casing has also been studied and efficiency improvements of 3% have been made in recent
years with the use of modern research tools. The efficiency of the turbine also depends on the
aerodynamics of the casing, deflectors, and injector covers [29]. However, major factors involved in
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the design of a turbine comprise the position of the jet, flow in the area of the lip, bend radius, and
weight of the turbine [30]. The flow of the water jet over the Pelton bucket has been analyzed in several
ways, initially in 2D with linear flow experiments [10] as shown in Figure 6, later with numerical
simulations [31], and with the use of cameras in the adjacent bucket that evaluates the flow more closely
[12, 32].
Figure 6. Representation of the sediment particles in the jet water over the buckets. a)
2D Representation of the path of sediments in the Pelton bucket [10]. b) 3D
Computational modeling of the sediments in the Pelton bucket [33].
Electron microscopes have also been used to monitor the type of erosion presented in each part of the
bucket [14, 34], which shows the action of the centripetal, Coriolis, and curved trajectory forces on the
sediment particles [35].
Figure 7. Representation of the evaluation of the behavior of the flow in black lines over the bucket
and the images from the electron microscope [35, 36].
(a)
(b)
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Many studies have been carried out in the areas of the turbine which are most susceptible to erosion,
with the help of experimental, numerical [37], and simulation tools [33]. For instance, the study of wear
zones and the type of sediment that affects those zones was carried out to show different erosion patterns
in different areas of the bucket which can be observed in Figure 7. The patterns that an eroded Pelton
turbine can have the combined effects of erosion, cavitation, and corrosion. However, it can have an
individual impact in some areas. The wave patterns depend on the turbine material's hardness, the
runner's speed, and sediment sizes, which are the main factors in the formation of undulations [10].
2.2. Measurement of erosion on Pelton turbines
The erosion measurement on the Pelton turbine is still carried out offline when the turbine unit is in the
complete stop stage. Different tools have been used for the measurement of changes in the surface of
the bucket. Some of the common tools are templates from the manufacturers, rulers, calipers, feeler
gauges, electronic thickness measurement tools, and/or 3D scanners which are dependent on the erosion
depth and the resolution to be achieved. The measurement of the changes in the thickness and profile
of the Pelton bucket is shown in Figure 8 [38, 39]. The locations and minimum number of measurement
points should be as per IEC 62364.
Figure 8. Graphic representation of most common measurement methods of erosion on the bucket of
the Pelton turbine. a) Templates and feeler gauges. b) Templates and calipers. c) Electronic thickness
measurement tools. d) 3D scanning.
Another powerful tool for the measurement and detection of cavitation, vortex, and bubbles in hydraulic
machinery is image processing. With image processing, it is possible to investigate the evolution of
cavitation and its effects on the blades [40, 41]. The use of image processing techniques has also been
applied to measure erosion in turbines [42, 43]. MATLAB is a tool widely used for processing images
and finding the ratio of the pixels and the eroded areas which are closest to the bucket tip and splitter
as shown in Figure 9. The use of machine learning has also been growing now and then for processing
images related to erosion to classify them [15]. Moreover, it has also been extensively in use to estimate
the degree of erosion on flat surfaces [44].
(a)
(b)
(c)
(d)
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Figure 9. Image processing techniques for measurement erosion in Pelton turbines.
a) Developed in MATLAB. b) Developed in Python [15, 42].
3. Maintenance of Pelton turbines
Proper maintenance of a Pelton turbine depends on physical condition, age of the asset, level of
technology installed, operating restrictions, and the maintenance required [45] as shown in the flowchart
in Figure 10. However, one of the principal factors is the way how it is managed in the operation, which
each company owner and the electrical system required to carry out in every powerplant. The researched
as well as tailored maintenance methodology such as Reliability Centered Maintenance (RCM) helps
to have a better operating factor if they are well implemented [46, 47].
Figure 10. Evaluation criteria for the type of operation and maintenance of a Pelton
turbine.
Operation and maintenance
of a Pelton turbine
Estimation of turbine
lifetime
Type of maintenance
applied.
Estimation of erosion type
as a function of sediment
High erosion
Rotation <= 1year
Medium erosion
Rotation 1 – 5 years
Low erosion
Rotation < 5 years
Inspection strategies
plus maintenance
Evaluation of the period
of preventive inspections
Gradual erosion
Erosion +
cavitation
Recuperations
Polishing and
repair on site
Minor workshop
maintenance
Major maintenance
and reconstructions
Coating
alternatives
Redesign +
upgrade
NDT and visual
inspections
(a)
(b)
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Welding is a widely used technique for the recovery of the profile of an eroded Pelton turbine. The
considerations for the estimation of the operation time between each maintenance depend on an
economic evaluation concerning the amount of erosion, the cost of maintenance, and the risk assumed.
In addition, for an estimation of the overall life of the Pelton turbine exposed to sediments, the amount
of erosion in the turbine, the profile recovered by welding, and subsequent heat treatment are needed.
These criteria are also necessary for an economic evaluation of improvements like coating or sediment
trap capacity.
3.1. Inspections
Inspections depend mainly on the type of wear that the turbine possesses. It may take several hours for
the inspection because of the complexity of the hermetic seal installation in the turbine chambers and
the assembly of structures which greatly depend upon the scope of the technical person authorized to
inspect the critical section of the turbine [48].
3.1.1. Hydropower plants with low sediment load
The inspections, for evaluation of the condition of the turbine, are carried out using visual inspections
technique and/or non-destructive tests (NDT). With the low sediment concentration, inspection is
mainly done to detect the beginning of fatigue fractures and the advancement of the erosion trend. These
inspection activities need to be carried out when the powerplant is in a complete stop state. Hence, they
are normally done in seasons of low water availability to reduce the economic impact on energy
production and the income from the availability of the unit in the system.
3.1.2. Hydropower plants with high sediment load
In hydropower plants with high sediment load, measurement, and inspection are carried out for the
evaluation of the severity of erosion. The erosion phenomenon accelerated in the rainy seasons forcing
the shutdown of units and resulting in the reduction of revenue.
3.2. Prevention of failures methods
The control of sediments and their management in Pelton turbines has been extensively studied for
reducing their passage through the turbine [8]. The measurement of sediments passing through power
plant facilities becomes more important nowadays and it can be periodical and online [13]. There are
some points for the locations for online systems for measurement and monitoring of sediment in the
powerplant with Pelton turbine as is shown in Figure 11.
Figure 11. Diagram of some points for the locations of online system measurement
of sedimentation in a typical Pelton hydropower plant.
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The principal online factors to be measured are the suspended sediment concentration (SSC) [49] and
its particle size distribution (PSD). Moreover, the combined dynamic imaging analysis (DIA) with
modern equipment for the measurement of the size and shape of sediments is supposed to provide good
results [50].
3.3. Coating on Pelton turbines
Coating in Pelton turbine buckets is the process of spraying hard ceramic material for its durability.
There are several types of materials as well as processes used for coating Pelton turbines [10]. These
techniques have been applied since the 1980s and have had good results in the reduction of erosion in
many power plants worldwide [51]. But on the other hand, in some sites, the coating could not withstand
a single rainy season as well. For instance, bad performance of coating was observed in Duck Canyon
HPP at Ancash in Peru and Khimti HPP in Nepal. The eroded surface of the turbine from the powerplant
is shown in Figure 12. Because of the passage of 7345 tons of sediments, the coated turbine of this
power plant operates for merely 1680 hours with an average of 30.15 MW.
Figure 12. Erosion on the coated turbine in Duck Canyon HPP, at Ancash Peru (42MW, 380m).
4. Repairs of a Pelton turbine
The repair of the turbine generally depends on the type of maintenance carried out on each plant. It can
be preventive, corrective, condition-based, or new maintenance approaches that are being customized
for the power plant. The turbine is one of the main assets of the hydropower plant and in case of its
failure, it can generate a significant impact on the integrity of the plant or the repair time which has a
direct impact on income generation. Vibration, for instance, is measured with online systems which
helps to detect the fault in the turbines and its impact on their operating conditions [48]. The
maintenance of the turbines can be done on-site or by removing them and transferring them to a
specialized workshop.
4.1. On-site repair
Minor maintenance works can be carried out on-site such as roughness polishing which reduces its wear
exponentially. In addition, minor repair works is carried out for small cracks or wear that normally
occurs outside the bucket root. This minor maintenance can be carried out after the inspections, to
reduce the inoperative time. It is related to several factors such as water availability, turbine integrity,
system requirement for standby, annual maintenance of all components, estimation of erosion on
turbines, and season. However, the most predominant one corresponds to the evaluation of business
profitability according to the methodologies or forms of maintenance used in each company. With the
help of vibration monitoring, failures can also be analyzed to generate preventive models [16].
4.2. Workshop repair
For the case of major repairs such as welding work for replacement of parts damaged by erosion, repair
of major cracks, or inspection in greater detail, it is necessary to remove the turbine and repair it in
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specialized workshops. In such cases, the replacement of the turbine takes more time due to the
maneuvers that should be performed for the heavy-weight turbines and the adjustment of their fastening
elements.
5. Recuperation of Pelton turbine
The runner repair process depends mainly on how much the bucket has eroded. It can range from a
simple polishing of the surfaces to completely regenerating the eroded surface of the buckets, as shown
in Figure 13. The process needs to have control of temperature and follow procedures according to each
runner. This uses lower temperatures to avoid changes in the structure of the base material. The use of
subsequent heat treatments is always predominant to recover the mechanical properties exposed to
temperature [52, 53].
Figure 13. Weld filler process in a bucket on a Pelton runner.
The recuperation process of a Pelton turbine has many steps, beginning with the erosion inspection, and
ending with static balancing, transportation, and proper storage. The main steps during the process are
welding, grinding, and various heat treatments as shown in Figure 14 in the specialist workshop, or
even automatized, depending on access to the workshops.
Figure 14. Main steps in the recuperation of the Pelton turbine by the welding process
6. Calculation of the lifetime of a Pelton turbine
Currently, there is no standard or established method to estimate the lifetime of a turbine [54]. The
references are the guarantees that are received with the new Pelton turbines which generally include
manufacturing faults and have a validity for a few years only. Similarly, World Bank's suggested
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lifetime evaluation is 10 years [55]. Turbines operated in water with low sediment concentration can
last up to 50 years or more. Sometimes turbines operating in sediment-laden rivers with high
concentrations have lasted more than 20 years. However, there are some cases of failures where turbine
runners lasted less than a year.
Asset management practiced on a Pelton turbine considers and analyzes the business requirements,
design, acquisition, operation, maintenance, modifications, and final disposal [56]. For this, an
important factor is maintainability and its projections according to the sediment condition are important
as depicted in Figure 15. The maintenance of a Pelton turbine involves visual inspections, non-
destructive tests (NDT), on-site maintenance, and major maintenance with partial or complete repairs.
Another important point in consideration during lifetime evaluation is the management of all the
components of the hydroelectric plant and the entire project, to have a complete overview of the
financial strategies that are used [57].
Figure 15. The life cycle of a Pelton turbine, from its commissioning to retirement in Peru.
Lifetime evaluation also considers the maintenance of the average life of the components. If there is a
need for major maintenance or replacement at some point, the financial evaluation of projects is carried
out with the help of Net Present Value (NPV) in addition to other methods such as the Internal Rate of
Return (IRR) or the Payback Period [58].
The calculation of the NPV using the Capital Asset Pricing Model (CAPM) [48] required the Weighted
Average Cost of Capital (WACC) which has a component called Country Risk Premium (CRP) [59].
CRP of the countries with high hydraulic potential in Pelton is also high [60] resulting in the WACC
being high. For example, in Nepal, the hydroelectric potential is 83 GW [61] and only 2.1GW has been
developed [62], which represents 2.5% of its capacity, and the CRP is 11.5% [63]. Therefore, the
WACC is higher [58] which is between 15.3% and 20.8% depending on the external or internal origin
of the capital [63]. In Nepal, the expected lifetime of a hydroelectric plant and its components including
civil works could only be 18 years if these factors are considered.
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Figure 16. Graphical representation of the net present value of future income in
different weighted average costs of capital.
The evaluation of the lifetime of the turbine carried out considering the project’s expected life is
different from project to project. In Figure 16, we can observe that the value of return on investment of
a project, with a WACC rate of 20% has a net present value of 4% of the investment after 18 years. On
the other hand, with the WACC rate of 7%, the same decrease in the value (i.e., 4%) will take 47 years.
Therefore, it is suggested to evaluate the hydropower projects for economically stable countries with
long-term years. While for the projects located in countries with high-risk country premiums, short
terms evaluation methods should be used [57].
The calculated financial lifetime of a Pelton turbine should consider the location and the WACC of the
hydropower plant including the cost for preventive maintenance as well as refurbishment/replacement
according to the exposure of sediment loads. The erosion of the turbine is one of the main factors that
must be calculated to forecast what type of maintenance is needed for the hydroelectric power plant.
7. Conclusions
Sediment erosion in the turbines operated in sediment-laden water is inevitable. Many investigations
have been made to understand the flow behaviors and the effect of sediments on the performance of the
turbine. Better turbine design and increased resistance of materials used for turbines in modern days are
contributing to the mitigation of sediment erosion. However, a comprehensive approach is required to
reduce its impact on such projects. Recently, state of art techniques like FEM and CFD are used to study
sediment erosion phenomenon and its effect evaluation not only on the performance but also on the
overall lifetime of the turbine. Similarly, image analysis is being utilized for estimating the flow
behaviors, in addition to the detection of cavitation and measurement of wear using various processing
tools with good results. Further, the lifetime estimation of a Pelton turbine is equally important which
mainly depends upon the operation and maintenance strategy used along with the sediment erosion
tendency. Although many investigations were made in understanding, evaluating, and forecasting the
sediment erosion in Pelton turbines, clear and concise results are yet to be achieved. Hence, more study
needs to be directed towards quantifying sediment erosion on Pelton turbines using modern tools and
techniques along with machine learning techniques. Furthermore, proper maintenance strategy and
methods need to be investigated for the proper financial estimation of the power plant in general.
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References
[1] Berga L 2016 The Role of Hydropower in Climate Change Mitigation and Adaptation: A
Review Engineering 2 313-8
[2] Lu X X, Ran L S, Liu S, Jiang T, Zhang S R and Wang J J 2013 Sediment loads response to
climate change: A preliminary study of eight large Chinese rivers International Journal of
Sediment Research 28 1-14
[3] Grill G, Lehner B, Thieme M, Geenen B, Tickner D, Antonelli F, Babu S, Borrelli P, Cheng
L, Crochetiere H, Ehalt Macedo H, Filgueiras R, Goichot M, Higgins J, Hogan Z, Lip B,
McClain M E, Meng J, Mulligan M, Nilsson C, Olden J D, Opperman J J, Petry P, Reidy
Liermann C, Sáenz L, Salinas-Rodríguez S, Schelle P, Schmitt R J P, Snider J, Tan F, Tockner
K, Valdujo P H, van Soesbergen A and Zarfl C 2019 Mapping the world's free-flowing rivers
Nature 569 215-21
[4] Flemming B W 2011 Treatise on Estuarine and Coastal Science, ed E Wolanski and D
McLusky (Waltham: Academic Press) pp 7-38
[5] E. Issa I, Al-Ansari N, Knutsson S and Sherwany G 2015 Monitoring and Evaluating the
Sedimentation Process in Mosul Dam Reservoir Using Trap Efficiency Approaches
Engineering 07 190-202
[6] Kondolf M and Yi J 2022 Dam Renovation to Prolong Reservoir Life and Mitigate Dam
Impacts Water 14 1464
[7] Misset C, Recking A, Navratil O, Legout C, Poirel A, Cazilhac M, Briguet V and Esteves M
2019 Quantifying bed‐related suspended load in gravel bed rivers through an analysis of the
bedload‐suspended load relationship Earth Surface Processes and Landforms
[8] Foldvik A, Silva A T, Albayrak I, Schwarzwälder K, Boes R M and Ruther N 2022 Combining
Fish Passage and Sediment Bypassing: A Conceptual Solution for Increased Sustainability of
Dams and Reservoirs Water 14 1977
[9] Annandale G W 2016 Extending the Life of Reservoirs: Sustainable Sediment Management for
Dams and Run-of-River Hydropower: The World Bank) pp 7-22
[10] Thapa B 2004 Sand Erosion in Hydraulic Machinery. In: Fakultet for ingeniørvitenskap og
teknologi, (Trondheim: Norges teknisk-naturvitenskapelige universitet)
[11] Chitrakar S, Neopane H P and Dahlhaug O G 2018: InTech)
[12] Perrig A, Avellan F and Farhat M 2007 High Speed Flow Visualisation of an Impinging Jet on
a Pelton Turbine Bucket
[13] (IEC) l E C 2019 IEC 62364 - Guidelines for dealing with hydro-abrasive erosion in kaplan,
francis, and pelton turbines. In: Hydraulic machines,
[14] Rai A K, Kumar A and Staubli T 2020 Effect of concentration and size of sediments on hydro-
abrasive erosion of Pelton turbine Renewable Energy 145 893-902
[15] Kraxner T 2022 Grading Erosion on pelton wheels from cavitation with images. pp II, 73 S1 -
II,
[16] Zhao W, Egusquiza M, Estevez A, Presas A, Valero C, Valentín D and Egusquiza E 2021
Improved damage detection in Pelton turbines using optimized condition indicators and data-
driven techniques Structural Health Monitoring 20 3239-51
[17] Osinergmin 2020 “Reserva Rotante para Regulación Primaria de Frecuencia”. (Perú
[18] Kubota T 1989 Observation of jet interference in 6-nozzle Pelton turbine Journal of Hydraulic
Research 27 753-67
[19] Mark Crawford A 2012 Lester Allan Pelton. In: The American Society of Mechanical
Engineers,
[20] Smith B T, Zhang Q F, Cones M and Anders J 2022 HAP Best Practice Catalog Revision 2.0.
(United States
[21] Erazo J, Barragan G, Pérez-Sánchez M, Tapia C, Calahorrano M and Hidalgo V 2022
Geometrical Optimization of Pelton Turbine Buckets for Enhancing Overall Efficiency by
Using a Parametric Model—A Case Study: Hydroelectric Power Plant
“Illuchi N2” from Ecuador. In: Energies,
[22] Solemslie B 2016 Experimental methods and design of a Pelton bucket.
Current Research in Hydropower Technologies 2023 (CRHT-XI)
Journal of Physics: Conference Series 2629 (2023) 012008
IOP Publishing
doi:10.1088/1742-6596/2629/1/012008
15
[23] Hahn F J J, Semlitsch B and Bauer C 2022 On the numerical assessment of flow losses and
secondary flows in Pelton turbine manifolds IOP Conference Series: Earth and
Environmental Science 1079 012082
[24] Andolfatto L, Morisod M, Dodier A and Gervais N 2022 AI-based approach to predict nozzle
instability in Pelton turbine model test IOP Conference Series: Earth and
Environmental Science 1079 012005
[25] Chiarelli M, Hasmatuchi V C, Amini A, Decaix J, Vetsch D F, Boes R M and Münch-Alligné
C 2022 On-site measurements of the dynamic behaviour of Pelton turbines in the
context of predictive maintenance IOP Conference Series: Earth and Environmental
Science 1079 012096
[26] Staubli T, Abgottspon A, Weibel P, Bissel C, Parkinson E and Leduc J 2009 Jet quality and
Pelton efficiency
[27] Zhang Z and Casey M 2007 Experimental studies of the jet of a Pelton turbine Proceedings of
the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 221 1181-
92
[28] Rentschler M, Weibel P, Isler P, Lais S and Gervais N 2022 Comparison of mechanical stress
in Pelton Buckets between simulation and measurement IOP Conference Series: Earth and
Environmental Science 1079 012070
[29] Quaranta E and Trivedi C 2021 The state-of-art of design and research for Pelton turbine casing,
weight estimation, counterpressure operation and scientific challenges Heliyon 7
e08527
[30] Solemslie B W and Dahlhaug O G 2014 A reference pelton turbine - design and efficiency
measurements IOP Conference Series: Earth and Environmental Science 22 012004
[31] Nielsen T K 2014 Flow in Pelton turbines. In: Fakultet for ingeniørvitenskap og teknologi,
(Trondheim: Norges teknisk-naturvitenskapelige universitet)
[32] Solemslie B and Dahlhaug O 2016 A reference Pelton turbine - High speed visualization in the
rotating frame IOP Conference Series: Earth and Environmental Science 49 022002
[33] Leguizamón S, Jahanbakhsh E, Alimirzazadeh S, Maertens A and Avellan F 2019 Multiscale
Simulation of the Hydroabrasive Erosion of a Pelton Bucket: Bridging Scales to
Improve the Accuracy. In: International Journal of Turbomachinery, Propulsion and
Power,
[34] Padhy M K and Saini R P 2012 Study of silt erosion mechanism in Pelton turbine buckets
Energy 39 286-93
[35] Rai A K, Kumar A and Staubli T 2019 Analytical modelling and mechanism of hydro-abrasive
erosion in pelton buckets Wear 436-437 203003
[36] Solemslie B W and Dahlhaug O G 2018 A Reference Pelton Turbine—Three-Dimensional
Flow Front Tracking Within a Rotating Pelton Bucket Journal of Fluids Engineering 140
[37] Ge X, Sun J, Zhou Y, Cai J, Zhang H, Zhang L, Ding M, Deng C, Binama M and Zheng Y
2021 Experimental and Numerical studies on Opening and Velocity Influence on
Sediment Erosion of Pelton Turbine Buckets Renewable Energy 173 1040-56
[38] Rai A, Kumar A and Staubli T 2015 DEVELOPING A TEST RIG TO MEASURE HYDRO-
ABRASIVE EROSION IN PELTON TURBINE
[39] Abgottspon A, Staubli T, Felix D, Albayrak I and Boes R 2014 Monitoring Suspended
Sediment and Turbine Efficiency Hydro Review Worlwide
[40] Xu Z, Kong F, Zhang H, Zhang K, Wang J and Qiu N 2021 Research on Visualization of
Inducer Cavitation of High-Speed Centrifugal Pump in Low Flow Conditions. In:
Journal of Marine Science and Engineering,
[41] Escaler X, Vilberg I K, Ekanger J V, Francke H H and Kjeldsen M 2018 Proceedings of the
10th International Symposium on Cavitation (CAV2018), ed J Katz: ASME Press) p 0
[42] Bim Prasad S, Bijaya G and Tri Ratna B 2007 Computational analysis of Pelton bucket tip
erosion using digital image processing. In: Proc.SPIE, p 68333C
[43] Bajracharya T, Joshi C, Saini R P and Dahlhaug O 2007 Correlation between Sand Led Erosion
of Pelton Buckets and Efficiency Losses in High Head Hydropower Schemes
Current Research in Hydropower Technologies 2023 (CRHT-XI)
Journal of Physics: Conference Series 2629 (2023) 012008
IOP Publishing
doi:10.1088/1742-6596/2629/1/012008
16
[44] Al-Bukhaiti M A, Abouel-Kasem A, Abdelrhman Y, Heshmat M and Ahmed S M 2022 Image
Processing Approach for Estimating the Degree of Surface Eroded by Slurry at Different
Impact Velocities Journal of Tribology 144
[45] Smith B T, Zhang Q F, Cones M and Anders J 2022 HAP Condition Assessment Manual
Revision 1.1. (United States
[46] Abregu J 2014 Plan de mantenimiento centrado en la confiabilidad para mejorar el factor de
disponibilidad de la central hidroeléctrica de Yuncan. In: Ingeniería Mecánica: Universidad
Nacional Del Centro Del Perú)
[47] Crespo Márquez A, Parra Márquez C, Gómez Fernández J F, López Campos M and González-
Prida Díaz V 2012 Asset Management: The State of the Art in Europe from a Life Cycle
Perspective, ed T Van der Lei, et al. (Dordrecht: Springer Netherlands) pp 81-99
[48] Modigliani F M, Merton H. Jun., 1958 The Cost of Capital, Corporation Finance and the Theory
of Investment The American Economic Review 48 261
[49] Felix D 2017 Experimental Investigation On Suspended Sediment, Hydro-Abrasive Erosion
And Efficiency Reductions Of Coated Pelton Turbines. ETH Zurich)
[50] Arora N, Kumar A and Singal S K 2022 Measurement of sediment particle size distribution and
shape using dynamic imaging analysis IOP Conference Series: Earth and
Environmental Science 1079 012063
[51] Felix D, Albayrak I, Abgottspon A and Boes R M 2016 Hydro-abrasive erosion of hydraulic
turbines caused by sediment - a century of research and development IOP Conference
Series: Earth and Environmental Science 49 122001
[52] Váz R F 2020 Welding and Thermal Spray Processes for Maintenance of Hydraulic Turbine
Runners: Case Studies. In: Welding and Inspections,
[53] Panthee A, Thapa B and Neopane H P 2015 Quality control in welding repair of Pelton runner
Renewable Energy 79 96-102
[54] Georgievskaia E 2018 Justification of the hydraulic turbines lifetime from the standpoint of the
fracture mechanics Procedia Structural Integrity 13 971-5
[55] WorldBank 2015 International Finance Corporation. 2015. Hydroelectric Power : A Guide for
Developers and Investors. (Washington, DC)
[56] O'Hanlon T 2016 ed Reliabilityweb.com® (https://reliabilityweb.com/)
[57] Morris G L a F 1998 Reservoir Sedimentation Handbook: McGraw-Hill Book Co.)
[58] Cornejo R 2017 Estructura de capital en mercados emergentes. Velocidad de ajuste de la
estructura de capital en las empresas peruanas cotizadas en bolsa. Universitat Ramon Llull
p 213
[59] Mecom 2016 Cálculo de la tasa WACC. ed M d Economia
[60] Morgan J P 2022 Index Product Guide.
[61] Thapa B, Shrestha R, Dhakal P and Thapa B 2004 Sediment in Nepalese hydropower projects
[62] Departement_of_electricity_development 2022 License Power Plants (Nov. 2022).
[63] Amatya A N 2018 Solution for estimating weighted average cost of capital, wacc, in frontier
markets.
Acknowledgments
The research work is conducted under research project FME-HydroCen. This project (No. 986490100)
is funded by Norwegian Research Council and Norwegian Hydropower Industries. Authors would like
to thank Prof. Ole Gunnar Dahlhaug from NTNU for his continuous support.
