Rotor-dynamic characteristics analysis of a large-scale Francis turbine shaft-system

The Francis turbine shaft-system consists of a hydraulic-turbine runner, generator-rotor, hydraulic-turbine shaft andgenerator shaft, which is the key component of the hydraulic-turbine unit, and the status of the shaft-systeminstallationaffects the safety and reliability of the hydraulic-turbine unit directly. The rotor-dynamic characteristics of a large-scaleFrancis turbine shaft-system under different rotating speeds were calculated with the finite-element method (FEM) inthis paper. The results show that the vibration motion of the studied shaft-system is a bending mode. The rotatingspeedof the unit has significant influences on the rotor-dynamic characteristics of the Francis turbine shaft-system, includingits natural-frequencies, vibration modes and critical-speed. By comparing the critical-speed with the rated and runawayspeed of the Francis turbine shaft-system, the evaluation shows that the shaft-system operates in safe conditions. Theresearch provides theoretical support and practical reference for on-site assembly, safe production and operationofprototype hydroelectric units. The conclusions can be extended to the high-quality installation and operation of other large hydroelectric generating units, pumps and pump-turbine units.