Development of advanced analytical techniques for the analysis of subsynchronous torsional interaction with FACTS devices

Summary form only given. The potential for subsynchronous torsional interaction (SSTI) with static VAr compensators (SVCs) and other FACTS devices has been considered in simulation studies as well as in real applications. System studies suggest that large SVCs could have a noticeable impact on torsional vibration modes of nearby generators especially under high-stress conditions. The SSTI sensitivity to SVCs appears from these investigations, mainly related to the dimension and location of SVCs as well as the effect of the voltage control loop and supplemental modulation controls at subsynchronous frequencies. Analysis of SSTI requires complete characterisation of both, the electromechanical dynamics and the electromagnetic dynamics of the network including representation of power system controls in the subsynchronous frequency range. As pointed out by several researchers, SSTI involving FACTS devices is a rather complicated phenomenon, which depends on several factors such as power flow and the interaction with other control devices and control actions. This paper presents some recent advances on the development of analytical techniques for the analysis of subsynchronous resonance (SSR) with AC transmission lines and SSTI with power system controls, namely SVCs and thyristor-controlled series capacitors (TCSCs). Emphasis is being placed on the analysis of the combined effect of series capacitor-compensated transmission lines and SVCs on torsional vibrations. An advanced linear state model of the power system that includes the representation of several FACTS devices is presented.