Protection for sub synchronous torsional interaction conditions using an industrial sub-harmonic relay

The Sub Synchronous Torsional Interaction (SSTI) conditions occurred due to the interactions of the generator-turbine systems and devices such as series compensated systems and HVDC systems has identified as harmful condition to avoid. Although it is a common practice to study and mitigate possibilities of SSTI conditions at system level designs, the power systems are not fully immune to SSTI conditions. This paper investigates the applicability of a numerical sub-harmonic relay for providing the protection against such SSTI conditions. Performance (accuracy and speed) of the proposed solution is investigated using various SSTI conditions injected into the relay.