Reciprocal impacts of PSS and line compensation on shaft torsional modes

In this paper, the effects of Power System Stabilizer (PSS) along with an uncompensated or series compensated transmission line on turbine-generator shaft torsional oscillations are investigated. Time domain simulations and eigenvalue analysis are carried out in MATLAB and SIMULINK to study the interaction between PSS and torsional modes. A six-mass shaft is employed to accurately study the torsional oscillations between the masses. The results show that under certain conditions, serious problems may occur between Low Pressure (LP) turbine and generator masses. Also, for a series compensated line, torsional oscillations are likely to occur between Intermediate Pressure (IP) and LP turbines on the shaft at certain levels of compensation. As opposed to electromechanical mode, the PSS not only cannot make any damping improvements to torsional oscillations, but also may even make the situation worse.