Robotic polishing of turbine runners

This paper presents the results of a partnership between Alstom and Hydro-Québec for the development of a new factory robotic polishing process. The goal is to improve turbine efficiency by reducing surface roughness to a level that is unattainable with conventional methods. Three entire axial-flow turbines for Hydro-Québec´s Sarcelle power station were polished with this new technique at the Alstom manufacturing plant in Sorel-Tracy as a pilot project between July 2010 and March 2011. The surface finish was lowered from Ra = 15 μm to Ra = 0.1 μm, and the waviness left by numerical control machining was grinded away at an overall rate of 5 h/m². The reduction of surface roughness from the standard IEC recommendation of Ra=3 μm to Ra=0.1 μm resulted in a 0.5% increase in turbine efficiency. This safe, new method proves its great potential for enhanced surface finish quality, productivity and worker safety.