A digital twin for torsional vibrations of power plant turbogenerators

Turbogenerators are important mechanical and electrical components in power plants. The steam turbines convert thermal energy into mechanical energy causing the rotor to spin. And the generator produces electrical energy by electromechanical interactions. The total energy is transferred via the air gap torque of the generator. For a safe and reliable operation, the mechanical-electrical interactions in the air gap of the generator and the resulting torsional vibrations of the shaft train must be observed very carefully. In case of disturbances in the electrical system, the excited transient torsional vibrations may become very large due to the low system damping. In such cases it is important to control the torsional vibration behaviour to guarantee acceptable vibration and stress levels. A Digital Twin is a suitable monitoring tool to solve this task. With a Finite Element Model (FEM) as part of the Digital Twin torsional vibrations can be calculated. And the real torsional vibrations are measured at selected locations of the shaft train with sensors. By comparison of measured and calculated torsional vibrations the vibration difference is introduced into a calibration loop of the Digital Twin, in which the system parameters as well as the air gap torque are continuously identified and adjusted. The Digital Twin can be used online, running permanently parallel to the real system as a monitoring system and as a detection system in case of system failures.