Study on damping scheme of subsynchronous resonance in a multi-machine system by combination of SEDC with STATCOM

When the outputs of parallel-operated multi steam turbine generator units in the same type are sent out via a transmission line with serial compensation, the subsynchronous resonance (SSR) may occur. When unequally loaded, the shafting torsional vibrations are different one another in amplitudes and phases. Taking a parallel-operated two-machine system composed of generators in the same type for example, the differences between torsional vibrations of the two shaftings under SSR are researched. Time-domain simulation results show that when rotating speed deviations of respective generators are taken as input signals, the torsional vibrations of all shaftings can be damped by using static var compensator (STATCOM) only, however the damping speed is slow; the combined damping measure composed of the STATCOM at grid side as the main means and the supplementary excitation damping control (SEDC) at generator side as the auxiliary means can damp SSR in multi generation unit system rapidly and effectively, meanwhile respective advantages of the two means in damping SSR can be brought into play.