Series compensation schemes reducing the potential of subsynchronous resonance

New series compensation schemes that reduce the potential of synchronous resonance problems in series compensated electrical power systems are presented. The schemes are phase-wise compensation schemes with three different combinations of inductive and capacitive elements. The combinations chosen have frequency characteristics that give equal reactances at the power frequency and unequal reactances at the other frequencies. This implies that the subsynchronous oscillations drive unsymmetrical three-phase currents. The developed electric torque, therefore, will be lower than what it would be if the three-phase currents were symmetrical. This results 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 subsynchronous oscillations will be suppressed, avoiding the build-up of torsional stresses on the generator shaft systems under subsynchronous resonance conditions. The validity and effectiveness of the schemes have been demonstrated on the Second IEEE Benchmark Model, by means of time simulation analysis using the EMTP program