Simulation of Sub-synchronous Resonance (SSR), and Mitigation of SSR by Static Synchronous Series Compensator with Lead Lag Compensator

Abstract

This research work presents a narrative method of alleviating the SSR problem using a static synchronous series compensator (SSSC). This method is based on using the SSSC to inject unbalanced series quadrature voltages and unbalanced shunt reactive currents in transmission line just after clearing faults. When the sub-synchronous oscillations drive unsymmetrical phase currents, the developed electromagnetic torque will be lower than the condition when three-phase currents are symmetrical. The unsymmetrical currents result in a lower coupling strength between the mechanical and electrical systems at asynchronous oscillations. Therefore, the energy exchange between the electrical and mechanical systems at sub-synchronous oscillations will be suppressed, thus avoiding build-up of torsional stresses on the generator shaft systems under sub-synchronous resonance condition. Stator current and voltage signals of synchronous generator are used as damping signals. In present work, SSR has been artificially developed by generating 3-phase LLL-G fault. Further, in order to mitigate this sub-synchronous resonance problem, lead lag compensator with SSSC is adopted. For analyzing effectiveness of this method, a Simulink model is developed and through results it has been concluded that the proposed method SSSC with lead lag compensator gives improved results.

Keywords: Lead lag compensator, quadrature voltage, SSR, static synchronous series compensator (SSSC), synchronous generator.