Determining Subsynchronous Damping Based on PMU Measurements from Finnish 400 kV Transmission Network

In May 2006 two Phasor Measurement Units were installed in Finnish 400 kV transmission grid in order to study subsynchronous damping of 950 MVA generating unit located geographically close to 550 MW HVDC transmission system. Subsynchronous damping was analyzed based on post- disturbance data measured using PMU. In this paper the background of the study and the main results from the measurements over period between May 2006 and August 2006 are presented. The quality of measured subsynchronous oscillations is illustrated and the validity of approach on subsynchronous damping estimation is discussed based on the measurements. Also, amplitude of measured subsynchronous components related to different system disturbances are illustrated and the values determined for total subsynchronous damping based on the post-disturbance measurements are presented. Finally, the possibilities to use PMU output data for real-time monitoring of subsynchronous damping is discussed based on the obtained experiences.