Effect of Surface roughness for Hydro Turbine Step-up Efficiency

Abstract: The energy produced by the flow of water is known as hydropower. It is an easily accessible and available source of energy in large quantity in the form of, rivers, lakes, streams and runoffs around the world. Hydropower is dependent upon hydrological cycle hence; this beneficial characteristic of hydropower makes it a renewable source of energy. Hydropower is free from poisonous emission; therefore, it is considered as a safer and pollution free source of energy. It is usually used to develop electricity from generators. These generators are connected to the hydro turbines by means of shaft. The electricity produced from hydropower is stable and steady because of its higher capacity, thus it can be a suitable source to work as base-load and used to balance the power fluctuations caused by varying loads. The hydropower can also be accommodated with different sources such as solar and wind system. This way of power sharing needs quick regulation as the deviation in the power grid changes rapidly. To fulfil this power demand with higher stability prompted to the development of modern turbines with more efficient, reliable and robust design.   To achieve the above target, it is of prime importance to improve efficiency of hydro turbine. Nevertheless, many methods are in practice for improvement for efficiency of the turbine; though one of the prime elements which influence the turbine efficiency is surface roughness. The effect of surface roughness differs for different turbine components like stay vanes, guide vanes, runner, draft tube and spiral casing.   The main purpose of this thesis is to examine the effect of surface roughness for hydro turbine step-up efficiency. It is based on reduced scale model to prototype conversion method. For this purpose, IEC_62097 has provided an excel sheet as an attachment for calculation. There has been always a need to perform model test, since performing test on the prototype itself is very accurate, and calculations too, do not yield reliable results. Therefore, the model to prototype conversion method is considered a better solution.   A sensitivity analysis is conducted on a Kaplan turbine situated at the Granfors power station located along the Skellefteå river about 30 km from the city of Skellefteå. The results obtained after applying the latest step-up expressions are described and presented. These outcomes have shown significant positive impact on the hydro turbine efficiency improvement, which are presented in graphs.   The most significant variations of step-up efficiency against surface roughness were observed in the runner part of the turbine. This specific characteristic makes it evident that more focus and test should be conducted on this part to improve efficiency.