The SVC voltage regulator can adversely affect the damping of the subsynchronous frequency torsional modes due to turbine-generator rotors and elastic shafts (constituting a lightly damped mass-spring-damper system). Unlike in the case of fixed series capacitors, the Torsional Interaction (TI) problem with SVC is not very significant. It has been suggested that the use of low pass filter or Transient Gain Reduction (TGR) in conjunction with the voltage regulator is adequate to overcome the problem.