Crack Formation on Francis Runners for Karun III Hydroelectric Project: Causes and Solutions

The KARUN III (KIII) hydroelectric project contains eight units equipped with vertical Francis turbines. The rated turbine output is 255 MW under a net head of 161m. Since 2006, some cracks were observed during regular inspections on the upper, lower and middle sections of blade outlet edges on some runners.The cracks were found to result from resonance phenomena accompanied with high level of hydraulic vibrations and noises measured in the units for high values ofturbine discharge. Numerical analysis and site measure ments declared that VON KARMAN vortices were responsible for the excitation frequency. Blade buttering of turbines runners was done to successfully prevent similar cracking in future

Keywords:

Francis Turbine , Crack , Runner blade , VON KARMAN , Resonance