Sub-synchronous Resonance through Torsional Mode Interactions: An Analysis

Interaction between electrical and mechanical systems, generally termed as sub-synchronous resonance (SSR) in power system, is not a straightforward problem to analyze as it involves detailed modeling of both systems. From the literature it is found that in most of the cases the SSR analysis is demonstrated through the IEEE first-benchmark system which contains many intricate modal interactions. To motivate the students to take up such standard systems for analysis, in this paper an example is presented which brings out the issues associated with the analysis by employing simplified models for generator and mechanical systems. Model and design equations are systematically derived so that any variations can be tried with ease. Case studies are presented to demonstrate the concept of modal interactions by studying the systems both in isolation and in combination. Eigenvalue analysis is carried out in addition to time-domain simulation to show that SSR is purely a discrete event.