Detection of Subsynchronous Torsional Oscillation Frequencies Using Phasor Measurement

This paper presents a noninvasive and easy-to-implement technique using phasor measurement units for accurate estimation of subsynchronous torsional frequencies. This information is relevant for the optimal design of high-voltage direct-current (HVDC) subsynchronous damping controllers that enhance the effect of HVDC on subsynchronous damping. The method is rigorously justified using mathematical proofs as well as thorough electromagnetic-transients simulations. The method was implemented in the Finnish transmission network and proved to be effective.