Abstract: There are various embedment options for the steel-lined spiral case of Francis turbine unit. Only constant-pressure option was adopted in the steel-lined spiral case in the  left bank hydropower plant of Three Gorges Project. To study the earthquake resistance of two embedment options for spiral case in the right bank hydropower plant, this paper presents a 3D finite element model to study the natural frequencies and seismic responses of steel-lined spiral case embedded under constant-pressure and embedded with supporting lining layer. Dynamic response of earthquake is calculated by the superposition of vibration modes. The analysis results indicate that different embedment options have little impact on structural natural frequency and seismic response. Both embedment options are feasible in earthquake resistance design, with the latter slightly better than the former.

Key words: Three Gorges hydropower plant, steel-lined spiral case, spiral case embedment options, seismic response