Wear Measurement of a Francis Runner damaged by sediment erosion: A case study

Abstract Hydropower is one the biggest sources of electricity all over the world and the largest by far in Nepal. Francis Turbines are extensively used in hydropower plants due to flexible ranges of head and discharge. Sediment erosion has been a major cause of damage and efficiency reduction in Francis Turbine components. As a stepping stone towards making erosion resilient turbine components, the measurement of wear due to erosion is essential. This study was conducted on the 35 MW Francis Runner installed at the Middle Marsyangdi Hydro Power Station of Nepal. The Runner was found to be heavily damaged after three years of continuous operation. The approach of measuring wear at various sections of the Runner using basic hand tools was adopted. The outer wearing rings on both the hub and shroud sections were found to be substantially reduced in diameter due to erosion, correlating to typical side wall erosion occurring in Francis Turbines. Substantial erosion was found on the blade inlets at both the hub and shroud sections, correlating to typical leakage gap erosion from the guide vanes. Substantial cavitation wear was found at the suction side of the blades at both the inlet and outlet of blades as well as at the wearing rings on both the hub and shroud sections. The wear on blades was found to be substantially higher at the outlet of the Runner with all 13 blades cracked at the outlet. The eroded mass of the Runner calculated through volumetric analysis was found to be 294 kg. The result was compared to the mass obtained by using a weight scale before and after the restoration of the Runner at a commercial workshop and a 5.16 % error was obtained which seems acceptable considering the simplicity of the process. The cost estimation for repairing the damaged Runner was also done based on the obtained result of eroded mass.