Low-amplitude subsynchronous oscillation(SSO)problem occurred frequently during operation of a supercritical 600 MW unit.To solve this problem

the Riccati transfer matrix method was applied to establish lumped-mass model for this unit.The torsional vibration natural frequency of shafting was solved

and the result was compared with the actual measured torsional vibration natural frequency of shafting.It was proved that the calculation results agreed well with the actual measured results

this model could be used to analyze the torsional vibration of this unit.Moreover

the relative value of torsional vibration stress shafting was solved based on the torsional vibration mode of this unit shafting

and the dangerous section of shafting was determined under SSO.The relationship between speed difference of the unit head and the fatigue life of the most dangerous section under SSO was established

the torsional vibration safety and fatigue life expenditure of the unit when the low-amplitude SSO occurred were evaluated.It provides important references for the same type units to analyze SSO.