Case StudyDevelopment of a test rig to evaluate abrasive wear on Pelton turbine nozzles. A case study of Chivor Hydropower
Introduction
Electric Power demand in Colombia is supplied mainly by hydraulic plants. They represent 64% of the total national installed capacity. Many hydro-plants are high head plants, with relatively small storage volumes or run of the river type of installations. In these environments, it is common to find fine silt, sand contaminated water and soil erosion in the catchment area. During the rainy season, contamination increases and all components in contact with the high-speed flow suffer from more aggressive erosion. Some of the solid particles are so small that large dams or settling tanks are not capable to remove them. Therefore, the most common concern in the maintenance of the hydro-equipment is worn components due to abrasive erosion. Suspended particles tend to erode surfaces by impacting them at certain angles. This modifies the surface roughness and generates cavitation due to increased localized turbulence [1]. Income and profits decrease as wear reduces the efficiency of power conversion. Additionally, that often results in increased shutdown time for maintenance. Most power companies recognize sediments as an ever-present problem depending on the water catchment behavior over time.
Experimental and theoretical research has been done to model and understand the effect of abrasive erosion in turbomachinery [2], [3], [4], [5]. However, it is difficult to extrapolate tribological phenomena [6] from one practical case to another because every water catchment has different silt and sand compositions. Consequently, each scenario should be analyzed independently. Furthermore, wear problems are not scalable. It creates the need to use tests that replicate the conditions of each environment as closely as possible.
As a result, some authors, [3,4]. [7,8] have developed erosion machines with speeds of up to 256 m/s, particles impacting at different large angles and diameters greater than 100 µm. However, there is no evidence of a test rig built to reproduce erosion and wear mechanisms with low angles and particles with an average diameter of less than 10 µm (Conditions observed in the AES Chivor Power plant).
The design and manufacture of the test rig described in this article was conceived to accurately replicate the wear mechanisms present in the ‘Chivor power station’. Regardless, the test rig was used to determine wear rate behavior of different materials and surface treatments. Wear rates of CrNi 13–45, CrNi 13–45 plasma nitrided and WC-Co-Cr thermal sprayed by HVOF were studied using the developed test rig.
Section snippets
Description of Chivor power station and wear context
Chivor is located 100 miles north of Bogota D.C., capital city of Colombia. The Esmeralda reservoir, with a storage capacity of 758 million cubic meters, receives from highland rivers a varied flow from a large water catchment area that has suffered destruction due to inadequate farming practices on steep slopes.
Two separate penstocks feed each four multi-jet Pelton type turbines for a total installed capacity of 1 GW. Each turbine has 6 jets; water jet speed is close to 120 m/s and a maximum
Test Rig
Fundamental data for the design of the test rig test was obtained by analyzing collected water samples from La Esmeralda dam and the information provided by the computer simulations. Water samples were collected during one year.
Mineralogical identification was made by XRD using the Rietvelt method and size distribution was measured using laser granulometric equipment. Sediment analysis showed that quartz was the main mineral present 42%, followed by kaolinite, anorthoclase and illite in 17%,
In situ wear measurement
In order to compare the wear generated in the erosion rig and the observed wear over the middle section of the needles, periodic inspections of the turbine needles of the hydroelectric power plant were conducted. Photographs and roughness measurements at the same locations were done during periodic visits to the plant. This information was recorded against operation time starting with new needles until they reached their average lifetime of 9000 hours. Direct measurement of material loss in the
Test rig effectiveness
In situ measurements provided description of needle wear development at the middle section, this consisted of three stages: The first stage (beginning of incubation) showed polishing of the surface, as a result of peaks of machined origin being removed resulting in Ra roughness values to decrease. The second stage (development of incubation), defined as the erosion due to impact at low angle, where roughness increases due particles cutting into the surface. The last stage (fast development),
Conclusions
The test rig described in this paper reproduces the erosion process occurring on the needles of the Chivor Hydro power plant. The test rig provided an experimental setup that closely replicates the wear mechanisms of like sediment particles plowing and wedging found in the field. The test rig is an effective experimental tool for evaluating the erosive wear resistance of any material in the search for life time improvements of hydraulic equipment.
Plasma nitride surface treatment increased the
Acknowledgment
The authors would like to thank specially AES CHIVOR management for their financial support through the project entitled "Development of Hydro-abrasive wear model for materials and process selection to reduce wear on Pelton turbine components at Colombian hydroelectric plants" under the call for Colciencias 2013. Many thanks to Chivor plant Engineers for all the information provided and used here. To all Mechanical Engineering Department personnel that participated in this project, many thanks
References (11)
- et al.
Renew. Sustain. energy Rev.
(2008) - et al.
Wear
(2011) - et al.
Energy
(2012) Wear
(2012)- et al.
Energy
(2012)
Cited by (23)
Machine learning regression tools for erosion prediction of WC-10Co4Cr thermal spray coating
2023, Results in Surfaces and InterfacesParticulate flow and erosion modeling of a Pelton turbine injector using CFD-DEM simulations
2022, Powder TechnologySediment-laden flow and erosion modeling in a Pelton turbine injector
2020, Renewable EnergyCitation Excerpt :Up to now, there are several experimental studies related to the sediment erosion of Pelton injectors, and most of them are descriptive investigations. For these studies, several field cases of worn injectors from Nepal, Norway, and Colombia were reported by Chitrakar [19], Thapa [20], and Morales et al. [21], respectively. Specifically, Bajracharya et al. [22] presented the profile of an eroded injector from the Chilime hydropower plant in Nepal and analyzed the erosion rate distribution on the needle surface in detail.
Interpretation and application of the hydro-abrasive erosion model from IEC 62364 (2013) for Pelton turbines
2020, Renewable EnergyCitation Excerpt :This clean energy contributes to the Sustainable Development Goals 7 and 13 of the United Nations. In the design and operation of hydropower plants (HPPs) located in geologically young mountains like the Himalayas, the Andes, the European Alps and the Pacific Coast ranges, sediment management is a major challenge [2–6]. While coarse sediments such as gravel and sand can be excluded from the river waters at the intakes of HPPs, it is not economically feasible to completely exclude silt and clay particles from the water entering hydraulic turbines.
Assessment of erosive wear of Pelton turbine injector: Nozzle and spear combination – A study of Chenani hydro-power plant
2020, Engineering Failure AnalysisCitation Excerpt :Erosion of spear nozzle tribo pair (in Pelton turbine) is a function of several parameters of erodents which includes their shape, size, hardness and concentration besides the discharge. Further distinct morphology of wear developed on eroded spear nozzle tribo pair has been demarcated into various zones on the basis of severity of wear patterns developed as per methodology proposed by Morales et al. [10]. The post mortem study includes wear mechanism and type of wear.
Hydro-abrasive erosion in Pelton turbine injectors: A numerical study
2019, Renewable EnergyCitation Excerpt :Evidence of the synergistic effect of the two phenomena in Pelton needles had been previously reported also by Thapa et al. [19] and discussed in the review paper by Gohil and Saini [20]. Recently, Morales et al. [21] estimated the erosion behavior of the needle at Chivor hydroelectric plant in Colombia by measuring the evolution of its surface roughness, and developed a setup to reproduce the phenomenon at the laboratory scale. The authors found that, after an incubation period, a fast increase in roughness occurred, and the enhancement in the mass removal was attributed to the fact that the hydro-abrasive erosion promoted the onset of cavitation erosion.
- 1
Corresponding research leader.