https://orcid.org/0000-0002-7658-2970
ABSTRACT
Sediment in the flowing water causes hydro-abrasive erosion of hydraulic turbines and other underwater components. In the present study, erosion quantification in the Kaplan turbine of a low-head hydropower plant (HPP) on the Upper Ganga Canal, is considered in the study. The study uses the guidelines of the International Electrotechnical Commission IEC 62364: 2019 for quantifying erosion in the Kaplan turbine. This work extends the research of Rai and Kumar (2016) and uses their primary details of some suspended sediment and operating parameters. The shape and mineral composition of the suspended sediment were quantified using dynamic imaging and X-ray diffraction techniques, respectively. The annual average particle load at the study HPP is obtained to be 356.87 kg·h/m3. Based on the analysis, it is estimated that the erosion depth varies from 0.88 to 1.37 mm/year at the blade tip, whereas from 2.40 to 3.74 mm/year at the blade outlet. At the runner chamber, the erosion depth varies from 1.27 to 1.98 mm/year. The erosion depth varies from 0.01 to 1.53 mm/year in the guide vanes. The calibration factor corresponding to the maximum erosion in guide vanes is estimated to be 1.75 × 10−5.
HIGHLIGHTS
Annual average sediment particle load at the study HPP is 356.87 kg·h/m3.
The erosion depth at the blade tip is 1.37.
The erosion depth at the blade outletis 3.74.
The calibration factor for the guide vane corresponding to maximum erosion is 1.75 × 10−5.
INTRODUCTION
Sediments in the flowing water are considered undesirable for hydropower projects, especially if the concentration is high and particles are abrasive. Sediments are responsible for reducing the life of the reservoir by causing reservoir sedimentation, reducing the efficiency of the turbine by causing hydro-abrasive erosion of turbine components; reducing the life of underwater concrete structures by hydro-abrasive erosion; reducing the performance of the oil cooling system by clogging its filters (Sangal et al. 2018; Rai et al. 2019b; Arora et al. 2022b, 2022a). Managing sediment in the run of river hydropower plants (HPPs) is an immense challenge. The desilting structures in HPPs are generally designed to remove sediment particles having a size greater than 200 μm (Arora et al. 2021; Pandey et al. 2021; Gupta et al. 2023). In peak sediment events, the performance of these structures may become inefficient, and the removal of desired particle size may not be completed; as a result, bigger size particles (>200 μm) may get transported to the turbine, causing hydro-abrasive erosion. Even the smaller size particles (<200 μm) are responsible for significant hydro-abrasive erosion (Padhy & Saini 2009, 2011; Rai et al. 2019a, 2020).
Hydro-abrasive erosion in hydraulic turbines is influenced by the parameters broadly characterized in three groups viz., suspended sediment parameters (concentration, size, shape, and mineral hardness), operating parameters (head, discharge, velocity, and angle of impingement), turbine material properties (type of material, hardness, elasticity, and morphology). The problem of hydro-abrasive erosion is common in the Himalayas, the Andes, the European Alps, and the Pacific Coast Ranges (Winkler 2014; Felix et al. 2016). Focusing on the Himalayas, the region is characterized by a steep topography, which plays a vital role in the spatial distribution of rainfall. High-intensity rainfall causes an uncommon streamflow event in the catchment, resulting in extensive slope instabilities, sediment transport, and floods (Pandey et al. 2018, 2020; Arora et al. 2022b). In a major study of the Himalayas, the maximum suspended sediment load (SSL) for the Alaknanda and Bhagirathi rivers at Devprayag has been estimated to be 8.1 × 106 t and 4 × 106 t, respectively. The Alaknanda and Bhagirathi rivers meet at Devprayag and form the Ganga River. The maximum SSL in the Ganges River has been estimated to be 9.1 × 106 t, characterized by a substantial coarse and medium silt quantity (Chakrapani & Saini 2009). The Himalayan sediment contains hard minerals (∼90%) that have a detrimental impact on the hydraulic turbine and other underwater components (Sangal et al. 2022; Arora et al. 2023, 2024b, 2024c)
The process of hydro-abrasive erosion depends upon suspended sediment parameters, operating parameters, and material properties of the turbine. Several researchers investigated the effect of sediment and operating parameters on different materials of the turbine using field, experiment, and numerical studies (Padhy & Saini 2011; Abgottspon et al. 2013; Khurana et al. 2014, 2016; Felix et al. 2016; Rai et al. 2020; Ud Din & Harmain 2020). Hydro-abrasive erosion of turbines results in cavitation, pressure pulsation, vibration, mechanical failure, and associated frequent shutdowns, which ultimately results in the reduction of the efficiency of HPP (Winkler 2014; Thapa et al. 2015; Rai et al. 2021). The combined effect of hydro-abrasive erosion and cavitation is sometimes observed, which is more significant than their individual effects (Thapa et al. 2007).
For the optimal operation of erosion affected HPPs, the quantification of erosion in hydraulic turbines and other underwater components is desirable. This quantification is challenging due to the large size of turbines, unevenly curved profiles, and varying erosion thickness. The traditional quantification methods use turbine templates and, general caliper, etc. (Ud Din & Harmain 2021). However, these methods only provide limited information. Further, precise quantification requires the consideration of several points on the profile. Such exercise becomes time-consuming and labor-intensive (Thapa 2004). To overcome this issue, a recent technique of 3D digitization may be used for easy and more informative erosion quantification. Several researchers have used this technique for quantifying erosion in model and prototype turbines (Abgottspon et al. 2013; Rai et al. 2017; Ud Din & Harmain 2020).
Although extensive studies on hydro-abrasive erosion of hydraulic turbines have been carried out, however, studies related to Kaplan turbine erosion are limited. International Electrotechnical Commission IEC 62364: 2019 prescribed guidelines to deal with the sediment erosion in the Pelton, Francis, and Kaplan turbines. These guidelines involve a relationship for quantifying the depth of erosion in the turbines by incorporating several operating and sediment parameters. Few terms used in the IEC 62364: 2019, like the flow coefficient 
and exponent 
of the reference size of the turbine, are not prescribed for Kaplan turbine erosion. In view of this, Rai and Kumar (2015) determined the values of both 
and p for runner blades and runner chamber by measuring the erosion in the prototype Kaplan turbine of Chilla HPP (144 MW) in the foothills of the Himalayas.
In the present study, a canal-based hydropower plant (HPP) located on the Upper Ganga Canal (UGC), India, is considered for erosion study in the Kaplan turbine. The study plant is located downstream of the Chilla HPP, where significant erosion of turbines takes place every year. Based on the available literature and experience, similar erosion conditions are expected to occur in the Kaplan turbines of Mohammadpur HPP. The hydro-abrasive erosion at the study HPP was predicted using IEC 62364: 2019 guidelines. Using the available details of the study HPP, 
and p were determined for guide vanes erosions. This study shall be helpful for the operators of Mohammadpur HPP in dealing with hydro-abrasive erosion and in the optimal operation of their HPP.
STUDY AREA
Mohammadpur HPP (9.3 MW) is a canal-based scheme on the UGC located in the Haridwar district of Uttarakhand state. The canal takes off from the Bhimgoda barrage, located 50 km upstream of the power plant. The discharge in the canal is regulated by UP Irrigation Department depending upon the irrigation requirement in the command area of the Irrigation canal. The salient features of Mohammadpur HPP are given in Table 1.
Salient features of Mohammadpur HPP
| S. No. | Particulars | Details |
|---|---|---|
| 1 | Location | Mohammadpur Village, Haridwar District, Uttrakhand State, India |
| 2 | Rated capacity | 9.3 MW |
| 3 | Rated head | 5.48 m |
| 4 | Rated discharge | 68 m3/s |
| 5 | Rated speed | 125 rpm |
| 6 | Turbine type | Vertical Kaplan (3 units of 3.1 MW each) |
| 7 | Runner diameter | 3,592 m |
| 8 | Number of blades | 4 |
| 9 | Number of guide vanes | 24 |
| 10 | Annual energy generation | 53.6 Million Units (MU) |
| 11 | Commissioning year | 1952 |
| 12 | Owner and operator | Uttarakhand Jal Vidyut Nigam Ltd |
| S. No. | Particulars | Details |
|---|---|---|
| 1 | Location | Mohammadpur Village, Haridwar District, Uttrakhand State, India |
| 2 | Rated capacity | 9.3 MW |
| 3 | Rated head | 5.48 m |
| 4 | Rated discharge | 68 m3/s |
| 5 | Rated speed | 125 rpm |
| 6 | Turbine type | Vertical Kaplan (3 units of 3.1 MW each) |
| 7 | Runner diameter | 3,592 m |
| 8 | Number of blades | 4 |
| 9 | Number of guide vanes | 24 |
| 10 | Annual energy generation | 53.6 Million Units (MU) |
| 11 | Commissioning year | 1952 |
| 12 | Owner and operator | Uttarakhand Jal Vidyut Nigam Ltd |
The lifespan of a typical HPP is usually 40–50 years. In the 1990s, the Mohammadpur HPP completed its design life, and its performance deteriorated. Having operated for 50 years, the generating units have derated, resulting in a restricted capacity of about 6,500 kW against the rated capacity of 9,300 kW. In view of this, the Department of Hydro and Renewable Energy (HRED), IIT Roorkee, carried out a performance analysis study of Mohammadpur HPP in October 2022. Based on the observations, the runner chamber, blades, stay ring columns, and guide vanes were extensively damaged due to erosion.
METHODOLOGY
The prediction of erosion depth in underwater parts of the Kaplan turbine was carried out using the International Standard IEC 62364: 2019 guidelines. This work extends the research of Rai & Kumar (2016) and uses their primary details of some sediment and operating parameters. The details of turbine erosion were taken from the Renovation Modernization and Uprating (RMU) report prepared by HRED, IIT Roorkee, in October 2002. These details were used for the analysis of erosion and determination of IEC 62364: 2019 calibration factor (CF) for erosion in guide vanes.
Erosion prediction
represents the erosion depth in mm; 
represents the particle load involving sediment concentration, size, shape, and hardness over a period of time; u is the characteristic velocity between the water and turbine components in m/s; 
represents the flow factor that relates erosion with flow pattern; 
represents the material factor that relates erosion with the surface of the material; 
represents the turbine reference size that relates to the curvature effects of erosion; p represents the exponent concerning the size-related effects of erosion.
represents the suspended sediment concentration (SSC) in kg/m3; 
represents the sediment size coefficient that is equivalent to the median particle size (d50) in mm; 
represents the shape coefficient that depends on the form of the particle; 
represents the hardness coefficient that is considered as the fraction of sediment hardness greater than the turbine material hardness; i is the typical time step out of the total n number of time steps. 
is the time step duration expressed in hours.
Suspended sediment parameters
Since Mohammadpur HPP is located downstream of Chilla HPP and there is no sediment removal structure exists in between, C and 
details were taken from the study of Rai & Kumar (2016). To obtain 
and 
, a suspended sediment sample collected from the Ganga River, was measured using two techniques. The shape of the sediment was measured using the dynamic imaging analysis (DIA) and accordingly the value of 
was determined (Arora et al. 2024a). The mineral composition of sediment was quantified using the X-ray diffraction (XRD) technique and the obtained minerals with hardness greater than 4.5 on the Mohs scale were considered for the determination of 
. The operating, sediment, and turbine material parameters values for Mohammadpur HPP are presented in Table 2.
IEC 62364: 2019 values for Mohammadpur HPP
| Parameter | Description | Values for study HPP |
|---|---|---|
| Wtip | Characteristic velocity at the blade tip | 33.73 m/s |
| Woutlet | Characteristic velocity at blade outlet | 37.64 m/s |
| Wchamber | Characteristic velocity at runner chamber | 15.56 m/s |
| Wgv | Characteristic velocity at guide vanes | 5.04 m/s |
 | Sediment size factor | 0.174 |
 | Sediment shape factor | 1.42 |
 | Sediment hardness factor | 0.86 |
 | Turbine material factor | 1 |
 2007,  2008,  2009,  2010,  2011 | Particle load for different years | (363.18, 379.60, 271.78, 346.38, 423.39) kg·h/m3 |
| Parameter | Description | Values for study HPP |
|---|---|---|
| Wtip | Characteristic velocity at the blade tip | 33.73 m/s |
| Woutlet | Characteristic velocity at blade outlet | 37.64 m/s |
| Wchamber | Characteristic velocity at runner chamber | 15.56 m/s |
| Wgv | Characteristic velocity at guide vanes | 5.04 m/s |
| | Sediment size factor | 0.174 |
| | Sediment shape factor | 1.42 |
| | Sediment hardness factor | 0.86 |
| | Turbine material factor | 1 |
| 2007, 2008, 2009, 2010, 2011 | Particle load for different years | (363.18, 379.60, 271.78, 346.38, 423.39) kg·h/m3 |
RESULT AND DISCUSSION
Erosion in turbine blades and runner chamber
Erosion depth at the blade tip, blade outlet, and runner chamber
| Year | PL (kg * h/m3) | Erosion depth (mm/year) | ||
|---|---|---|---|---|
| At blade tip | At blade outlet | At runner chamber | ||
| 2007 | 363.18 | 1.17 | 3.21 | 1.70 |
| 2008 | 379.60 | 1.23 | 3.35 | 1.77 |
| 2009 | 271.78 | 0.88 | 2.40 | 1.27 |
| 2010 | 346.38 | 1.12 | 3.06 | 1.62 |
| 2011 | 423.40 | 1.37 | 3.74 | 1.98 |
| Year | PL (kg * h/m3) | Erosion depth (mm/year) | ||
|---|---|---|---|---|
| At blade tip | At blade outlet | At runner chamber | ||
| 2007 | 363.18 | 1.17 | 3.21 | 1.70 |
| 2008 | 379.60 | 1.23 | 3.35 | 1.77 |
| 2009 | 271.78 | 0.88 | 2.40 | 1.27 |
| 2010 | 346.38 | 1.12 | 3.06 | 1.62 |
| 2011 | 423.40 | 1.37 | 3.74 | 1.98 |
Erosion in the Kaplan blade of Bhudkalan HPP (16 MW).
Particle load v/s erosion at (a) blade tip, (b) blade outlet, and (c) runner chamber for the year 2007.
Particle load v/s erosion at (a) blade tip, (b) blade outlet, and (c) runner chamber for the year 2007.
Cumulative particle load v/s cumulative erosion at (a) blade tip, (b) blade outlet, and (c) runner chamber for the years 2007–2011.
Cumulative particle load v/s cumulative erosion at (a) blade tip, (b) blade outlet, and (c) runner chamber for the years 2007–2011.
Erosion in guide vanes
There are 24 guide vanes in each turbine unit; the erosion details of all guide vanes were examined, and the maximum, minimum, and average erosion values and their corresponding CF values were obtained. The erosion depth values and their obtained CF values are presented in Table 4. The erosion depth ranges from a minimum of 0.01 mm/year to a maximum of 1.53 mm/year, which is quite high with respect to a turbine unit of 3.3 MW capacity. Due to such clearance between the collar and facing plate, significant leakages in the system and high losses in the turbine efficiency are evident. A similar case of erosion occurred in Jhimruk HPP (12 MW), where considerable erosion in runner blades, guide vanes, and facing plates resulted in an efficiency loss of 4–8% for a full load to part load condition (Pradhan 2004). The obtained CF values for guide vanes vary from a minimum of 3.55 × 10−8 to a maximum of 1.75 × 10−5. These values may be used to predict the erosion of guide vanes with similar operating and sediment parameters.
Erosion depth values in the guide vanes and corresponding calibration factors
| Turbine unit | Erosion depth (mm/year) | Calibration factor (CF) | |
|---|---|---|---|
| 1 | Maximum | 0.19 | 2.15 × 10−6 |
| Minimum | 0.01 | 3.55 × 10−8 | |
| Average | 0.08 | 9.28 × 10−7 | |
| 2 | Maximum | 0.43 | 4.95 × 10−6 |
| Minimum | 0.02 | 2.52 × 10−7 | |
| Average | 0.18 | 2.01 × 10−6 | |
| 3 | Maximum | 1.53 | 1.75 × 10−5 |
| Minimum | 0.01 | 9.17 × 10−8 | |
| Average | 0.29 | 3.27 × 10−6 |
| Turbine unit | Erosion depth (mm/year) | Calibration factor (CF) | |
|---|---|---|---|
| 1 | Maximum | 0.19 | 2.15 × 10−6 |
| Minimum | 0.01 | 3.55 × 10−8 | |
| Average | 0.08 | 9.28 × 10−7 | |
| 2 | Maximum | 0.43 | 4.95 × 10−6 |
| Minimum | 0.02 | 2.52 × 10−7 | |
| Average | 0.18 | 2.01 × 10−6 | |
| 3 | Maximum | 1.53 | 1.75 × 10−5 |
| Minimum | 0.01 | 9.17 × 10−8 | |
| Average | 0.29 | 3.27 × 10−6 |
UNCERTAINTY MEASUREMENT
denotes n number of basic independent variables, δY is the absolute uncertainty in the measurement of Y, which is a function of basic independent variables; 
denotespossible error in measurement (absolute uncertainty) of basic independent variablesThe uncertainty in the measurement of 
was computed as 0.65%. Rai & Kumar (2016) reported the uncertainty in the measurements of C and 
as 2 and 1.92%, respectively.
CONCLUSION
The present study investigates hydro-abrasive erosion in the Kaplan turbine of Mohammadpur HPP in the foothills of the Himalayas. The HPP is located on the UGC, where significant suspended sediment passes through the turbines every monsoon season. The study applies the IEC 62364 guidelines in quantifying the erosion in the Kaplan turbine. The predicted erosion depth values depict that the trailing edge erosion is more significant than (∼3 times) tip blade erosion. Also, significant erosion potential has been observed at the runner chamber. RMU report of the HPP reveals high erosion of guide vanes, particularly between the collars and facing plates. It is observed that the erosion depth varies considerably for turbine blades, runner chamber, and guide vanes for the same year as well as different years. This statement is true for both predicted and actual erosion values. Also, the quantum of erosion in the guide vane varies significantly for different turbine units. The site-specific calibration factors corresponding to maximum, minimum, and average erosion are determined for guide vane erosion. These calibration factors may be used to predict erosion of the guide vanes with similar operating and sediment parameters. This study shall be helpful for the operators of Mohammadpur HPP in dealing with hydro-abrasive erosion and in the optimal operation of their HPP. Similar studies on other erosion-affected HPPs shall contribute to better quantification of erosion and enhancement of calibration factors.
In the present analysis, details of erosion and sediment properties, such as SSC and size, were used from the RMU report and literature. The estimation of 
and 
is based on the analysis of a single sediment sample. Analysis of more sediment samples will increase the accuracy of such estimations. The erosion outcomes of runner blades and runner chamber are based on the prediction as per IEC 62364 (2019) guidelines and may differ from the actual turbine erosion. The future version of the study will include the comparison of predicted outcomes and field measurements.
ACKNOWLEDGEMENTS
The authors sincerely acknowledge the Ministry of New and Renewable Energy, Government of India, for providing PhD scholarship to the first author.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.
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