Analyzing Subsynchronous Torsional Interactions in Large-Scale Power Systems in Frequency Domain

This paper presents a generic technique for analyzing subsynchronous torsional interaction (SSTI) between series capacitors and multi-mass shaft system in steam turbine-generators. The proposed method focuses on application of the method in large-scale power systems where the SSTI study is to be carried out for large number of generators, different compensation levels, and various contingencies. The proposed methodology encompasses three steps: 1) Performing a network frequency scan to identify generators that are likely to show SSTI, also called critical generators; 2) Finding local mode of critical generators to identify critical torsional modes that are likely to interact with series capacitors; 3) Using frequency of critical modes as initial guess to trace them in the full system and find associated damping. This three-step procedure reduces computational cost while minimizing possibility of missing any torsional interaction in the system. Moreover, the developed procedure highly automates the process of finding subsynchronous modes and minimizes user interaction.