Impact of fault clearing time on shaft torque amplification in series compensated system

Series capacitor compensation in AC transmission systems may cause subsynchronous resonance (SSR) that can lead to turbine-generator shaft fatigue. One of the SSR phenomenons is referred to as shaft torque amplification, which might cause serious damage to the shaft. A methodology considering shaft torque as the torsional system response of applied force is given in this paper. The maximum shaft torque is finally deduced as an analytic function of fault clearing time using a simplified two-DOF model. The conclusion could be obtained that fault clearing at odd numbers of half cycles of the dominant torsional mode will generally provide maximum torques. Simulation results demonstrate the validity of the conclusion, which helps in choosing a proper fault clearing time that could avoid shaft damage and decrease reduction of shaft life efficiently.