Subsynchronous oscillation principle

Adopting series capacitance compensation in AC transmission system is a very economical method to improve transmission capacity, control power distribution between parallel lines and enhance transient stability of power system. However, series capacitor compensation may cause subsynchronous resonance of power system, and then damage the shafting of steam turbine generator set. The causes and effects of subsynchronous resonance can be described from three different aspects, namely, induction generation effect (IGE), electromechanical torque interaction (TI) and transient torque amplification (TA). For subsynchronous resonance, the main concern is the damage of shafting caused by torsional stress. Long-term accumulation of low-amplitude torsional vibration or short-term high-amplitude torsional vibration can cause shafting damage.

The torsional vibration of turbogenerator shafting caused by DC drive is different from that caused by series capacitor compensation in mechanism, because the former has no resonant circuit, so it is no longer called SSR, but SSO, which makes the meaning more extensive.