Pelton Turbine Bucket Research Articles

Improving the surface properties of a Pelton turbine bucket via centrifugal casting technique

This study examines the possibility of fabricating a complex, non-cylindrical, Pelton turbine bucket by centrifugal casting technique. Oil hardening non-shrinking die steel material was selected fo...

Correlation Development for Erosive Wear Rate on Pelton Turbine Buckets

Correlation Development for Erosive Wear Rate on Pelton Turbine Buckets

Forces acting on particles in a Pelton bucket and similarity considerations for erosion

High sediment transport rates cause severe erosion issues in hydropower plants leading to interruptions in power generation, decrease in efficiency and shutdown for repair and maintenance. For Pelton turbines operating at high head, the issue of erosion is severe, especially in components like buckets, nozzle rings and needles. Goal of the study is to develop erosion focussed guidelines for both designing as well as operating hydropower plants with Pelton runners. In this study, the flow of sediment inside a Pelton bucket with respect to forces acting on solid particles is analysed with an analytical approach by considering different dynamic forces originating from the rotation of the turbine, the curvature of the buckets, and the Coriolis effect. Further, the path of sediment particles and its effect on erosion phenomena are analysed based on the process of separation of different sized sediment particles from streamlines.The data relating to head, power, discharge, number of jet and efficiency of 250 hydropower plants installed all over the world were analysed in this study to find the major factors related to erosion in Pelton turbine bucket. From analysis of different force ratios, it is found that an increase of D/B, i.e. the ratio of pitch circle diameter and bucket width, and/or decrease of specific speed (nq) enhances erosion. As the erosion process depends significantly on nondimensional parameters D/B and nq, these are considered as similarity measures for scaling of the erosion process in the Pelton buckets of various sizes.

Investigation of Functionally Graded Aluminium A356 Alloy and A356-10%SiC<sub>p</sub> Composite for Hydro Turbine Bucket Application

The study investigates the application of centrifugal casting process in the production of a complex shape component, Pelton turbine bucket. The bucket materials examined were functionally graded aluminium A356 alloy and A356-10%SiCp composite. A permanent mould for the casting of the bucket was designed with a Solidworks software and fabricated by the combination of CNC machining and welding. Oil hardening non-shrinking die steel (OHNS) was chosen for the mould material. The OHNS was heat treated and a hardness of 432 BHN was obtained. The mould was put into use, the buckets of A356 Alloy and A356-10%SiCp composite were cast, cut and machined into specimens. Some of the specimens were given T6 heat treatment and the specimens were prepared according to the designed investigations. The micrographs of A356-10%SiCp composite shows more concentration of SiCp particles at the inner periphery of the bucket. The maximum hardness of As-Cast A356 and A356-10%SiCp composite were 60 BRN and 95BRN respectively, recorded at the inner periphery of the bucket. And these values appreciated to 98BRN and 122BRN for A356 alloy and A356-10%SiCp composite respectively after heat treatment. The prediction curves of the ultimate tensile stress and yield tensile stress show the same trend as the hardness curves.

MODELING AND STUDY OF HYDROELECTRIC GENERATING SETS OF SMALL HYDRO POWER PLANTS WITH FREQUENCY-CONTROLLED PERMANENT MAGNET SYNCHRONOUS GENERATORS

Currently, the hydroelectric generating sets of small HPPs with Pelton turbines employ as their generating units conventional synchronous generators with electromagnetic excitation. To deal with the torque pulsatile behaviour, they generally install a supplementary flywheel on the system shaft that levels the pulsations. The Pelton turbine power output is adjusted by the needle changing water flow in the nozzle, whose advancement modifies the nozzle area and eventually – the flow. They limit the needle full stroke time to 20–40 sec. since quick shutting the nozzle for swift water flow reduction may result in pressure surges. For quick power adjustment so-called deflectors are employed, whose task is retraction of water jets from the Pelton turbine buckets. Thus, the mechanical method of power output regulation requires agreement between the needle stroke inside the turbine nozzles and the deflector. The paper offers employing frequency-controlled synchronous machines with permanent magnets qua generating units for the hydroelectric generating sets of small HPPs with Pelton turbines. The developed computer model reveals that this provides a higher level of adjustability towards rapid-changing loads in the grid. Furthermore, this will replace the power output mechanical control involving the valuable deflector drive and the turbine nozzle needles with electrical revolution rate and power output regulation by a frequency converter located in the generator stator circuit. Via frequency start, the controllable synchronous machine ensures stable operation of the hydroelectric generating set with negligibly small amount of water (energy carrier). Finally, in complete absence of water, the frequency-relay start facilitates shifting the generator operation to the synchronous capacitor mode, which the system operating parameter fluctograms obtained through computer modeling prove.

Numerical simulation of cavitation flow characteristic on Pelton turbine bucket surface

The internal flow in the rotating bucket of Pelton turbine is free water sheet flow with moving boundary. The runner operates under atmospheric and the cavitation in the bucket is still a controversial problem. While more and more field practice proved that there exists cavitation in the Pelton turbine bucket and the cavitation erosion may occur at the worst which will damage the bucket. So a well prediction about the cavitation flow on the bucket surface of Pelton turbine and the followed cavitation erosion characteristic can effectively guide the optimization of Pelton runner bucket and the stable operation of unit. This paper will investigate the appropriate numerical model and method for the unsteady 3D water-air-vapour multiphase cavitation flow which may occur on the Pelton bucket surface. The computational domain will include the nozzle pipe flow, semi-free surface jet and runner domain. Via comparing the numerical results of different turbulence, cavity and multiphase models, this paper will determine the suitable numerical model and method for the simulation of cavitation on the Pelton bucket surface. In order to investigate the conditions corresponding to the cavitation phenomena on the bucket surface, this paper will adopt the suitable model to simulate the various operational conditions of different water head and needle travel. Then, the characteristics of cavitation flow the development process of cavitation will be analysed in in great detail.

A Study of Silt Erosion on Inner Buckets of Pelton Turbines

A 3-D model of pelton turbine bucket was built to investigate the motion characteristics of sediment particles in pelton turbines and the erosion caused by the movement. With the assistance of fluid analysis software FLUENT, A continuous phase turbulence model was estimated by the Euler equation which achieved convergence and the selected coupled calculation for solid-liquid two-phase flow with DPM model was built. It can be draw from the numerical analysis that, with the same size and sediment concentration, the inner bucket wall would suffer from the greater erosion by the relatively greater flow velocity; under the same condition of flow velocity and sediment concentration, the more serious erosion was caused by the bigger sized sediments; and the greater sediment concentration led to greater erosion, given the same flow velocity and sediment size. Based on the study, it showed that the erosion of inner wall of buckets was mainly affected by sediment size and concentration, as well as flow velocity.

Imposing angle boundary conditions on B-spline/NURBS surfaces

In this paper, we study the construction of a B-spline surface satisfying prescribed angle distribution (with respect to a chosen vector) of tangent planes along its boundary curve. This problem arises e.g. in a creation of a parametric geometric model of a Pelton turbine bucket, where specific angle distributions along a splitter and an outlet curve have to be fulfilled in order to control the flow of water into and out of the bucket. We prove that for a given B-spline curve c(t), t∈[0,1], the exact solution exists only in very special cases (for a special form of an angle function f(t)). Further, we formulate an algorithm for finding an approximate solution. We also derive a bound on its approximation error and give a numerical evidence that the approximation order of the proposed algorithm is four. Finally, the method is demonstrated on several examples.

A reference pelton turbine - design and efficiency measurements

The Pelton turbine has been subject to a varying degree of research interest since the debut of the technology over a century ago. Despite its age there are gaps in the knowledge concerning the flow mechanisms effecting the flow through the turbine. A Pelton turbine has been designed at the Waterpower Laboratory at NTNU. This has been done in connection to a Ph.D. project focusing on the flow in Pelton turbine buckets. The design of the turbine has been conducted using in-house knowledge in addition to some comments from a turbine producer. To describe the geometry multiple Bezier curves were used and the design strategy aimed to give a smooth and continuous gradient along the main flow directions in the bucket. The turbine has been designed for the operational conditions of the Pelton test rig installed at the Waterpower Laboratory which is a horizontal single jet test rig with a jet diameter(ds) of 35 mm. The diameter(D) of the runner was set to 513 mm and the width(W) of a bucket 114 mm, leading to a D/W ratio of 4.5. Manufacturing of the turbine has been carried out in aluminium and the turbine has undergone efficiency testing and visual inspection during operation at a head of 70 m. The turbine did not performed as expected and the maximum efficiency was found to be 77.75%. The low efficiency is mainly caused by a large amount of water leaving the bucket through the lip and hence transferring close to zero of its energy to the shaft. The reason for the large lip loss is discussed and two possible causes are found; the jet is located too close to the lip, and the inner surface of the bucket does not lead the water away from the lip. The turbine geometry and all data from both measurements and simulations will be available upon request in an effort to increase the amount of available data concerning Pelton turbines.

Study of silt erosion mechanism in Pelton turbine buckets

In the present study, an experiment was carried out to investigate the mechanism of erosion of a small scale Pelton turbine, under actual flow conditions. Samples of silt were collected from the head work of one of the most silt affected hydro power station in India. Silt parameters (silt particle size and silt concentration) were considered to investigate the mechanism of silt erosion on Pelton turbine buckets for different silt sizes. In the first part of the experimentation, hot spots (spots which are more prone to erosion) were identified under a high silt concentration. Second part of the experimentation was carried out to study the erosion mechanism for small specimens of metal which were fixed at the marked hot spots.Based on the investigation, it has been found that silt size is a strong parameter to produce erosion and the material removal from the surface is due to plastic deformation and ploughing of surface.

Study of silt erosion on performance of a Pelton turbine

The erosion of turbine components causes the decrease in turbine efficiency; increase in the maintenance cost and down time for turbine repair. All these factors contribute to the plant cost and cause the revenue losses. It is, therefore, essential to study the amount of efficiency loss owing to the erosion of turbine components due to the silt particles coming in water. The present study has been carried out to investigate the effect of silt erosion for different silt laden parameters and operating parameters such as silt concentration, size of silt particles, jet velocity and operating hours of the turbine on efficiency loss in Pelton turbine buckets.

Effect of size and concentration of silt particles on erosion of Pelton turbine buckets

Erosive wear of hydro turbine runners depends upon different parameters such as size, hardness and concentration of silt particles, velocity of flow, properties of the base material of the turbine components and operating hours of the turbine. Various researchers have conducted experiments to study the effect of these parameters on erosive wear. Most of these experiments were on small-size samples at different types of test rigs to simulate the flow conditions in turbines, however actual flow conditions and the phenomenon of erosive wear are too complex to simulate. Under the present study, effect of these parameters on erosion in actual conditions has been investigated experimentally. An extensive experimental study has been carried out on a small scale Pelton turbine. Based on the experimental data collected for different parameters, correlations have been developed for wear rate of Pelton turbine buckets as a function of critical parameters, i.e., size and concentration of silt particles and jet velocity.

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

Erosion of hydro turbine components through sand laden river water is one of the biggest problems in the Himalayan region. This problem exists for all kinds of turbines. Apart from erosion of buckets, erosion was also observed in nozzle of the Pelton turbines due to sand particles and such problem was observed in 22 MW Chilime Hydropower Plant in Nepal. Detailed studies were conducted and erosion analysis was carried out in this case study. Sieve and mineral content analyses were systematically carried out and sediment load was calculated. By doing this, erosion rate and efficiency reduction were established using already known methodology and scenario for similar hydropower plants. The flow analysis through surface of needle was established by drawing flow net diagrams. This detrimental damage led to efficiency reduction of 1.21% consequently resulting 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.

Flow in a Pelton Turbine Bucket: Numerical and Experimental Investigations

The aim of the paper is to present the results of investigations conducted on the free surface flow in a Pelton turbine model bucket. Unsteady numerical simulations, based on the two-phase homogeneous model, are performed together with wall pressure measurements and flow visualizations. The results obtained allow defining five distinct zones in the bucket from the flow patterns and the pressure signal shapes. The results provided by the numerical simulation are compared for each zone. The flow patterns in the buckets are analyzed from the results. An investigation of the momentum transfer between the water particles and the bucket is performed, showing the regions of the bucket surface that contribute the most to the torque. The study is also conducted for the backside of the bucket, evidencing a probable Coanda interaction between the bucket cutout area and the water jet.