Effect of blade friction on performance of Micro-Hydro pelton turbines : mathematical modeling and experimental verification

Abstract

Water turbines have been used in electricity generation for well over a century. Hydroelectricity now supplies 19% of world electricity and 44% (as at 2012) of Sri Lanka's electricity also comes from hydropower. Micro Hydro is a term used for hydroelectric power installations that typically produce up to 20 kW of power in Sri Lankan context. Many Micro-hydro power plants are operated with Pelton turbines. The main reasons for using Pelton turbines are that they are very simple and relatively cheap. As the stream flow varies, water flow to the turbine can be easily controlled by changing the number of nozzles or by using adjustable nozzles. Since most of the micro hydro Pelton turbines are now manufactured locally, it was revealed that much attention is not paid to the surface finish of the turbine buckets. On the other hand due to sand erosion of turbine parts bucket surface are getting rough day by day. Most of the research that had been done on turbines were focused on improving the performance with particular reference to turbine components such as shaft seals, speed increasers and bearings. There is not much information available on effects of blade/bucket friction on the performance of Pelton turbine. The main objective of this research is to analyze the performance of Micro hydro Pelton turbine particularly with respect to their blade friction. The governing laws of fluid dynamics, relevant to the application were used to develop a theoretical model to estimate the effect of blade friction on Pelton turbine performance. Then the developed mathematical model was validated experimentally. All the experiments are carried out in a Pelton turbine standard test bench. The power developed by the turbine was measured by keeping all the relevant parameters that affect to the power development, constant other than the friction of the bucket. The friction of the buckets was varied by varying surface roughness of the buckets. Different roughnesses of the surface was obtained by pasting various grades of sands one at a time on the surface of the buckets . It was concluded from the developed mathematical model and the experimental testing that power developed by a Pelton turbine increases when the surface roughness of the turbine bucket decreases. It was also proved from the research that splitter thickness of the buckets is also affect the power developed by the turbine. When the thickness of the splitter increases power developed by the turbine decreases. Therefore it is recommended from the study that Pelton turbine buckets must be smooth as much as possible and splitter of the buckets should be as sharp as much as possible to generate more power from a power plant.