As the landscape of energy production in Europe and other developed countries undergoes a rapid shift towards renewable energies, such as offshore wind, the use of HVDC (High-Voltage Direct Current) technology is increasing. HVDC converter stations have been reported to potentially cause sub-synchronous torsional interaction (SSTI) with turbo-generators in the grid. This phenomenon implies a negative electrical damping at the turbo-generator which may result in non-attenuating torsional vibrations. This is especially an issue in power grids where the close proximity of the power stations to the HVDC converter stations cannot be avoided. Therefore, in order to ensure safe and stable operation, monitoring of torsional vibrations is required.
In this article, a proof-of-concept study of touchless torque sensing at a nuclear power train in Gösgen, Switzerland, is presented. All three sub-synchronous natural frequencies were detected by the torque sensor during a load rejection test and show very good agreement with theoretical predictions based on finite element calculations. Possibilities to devise monitoring and eventually protection systems for torsional vibrations based on this technology are also discussed.