In recent years

with large amounts of power electronic equipments connected to power systems

subsynchronous oscillation is becoming increasingly complicated. So it is difficult to identify the main cause of oscillation. Disturbance source location of subsynchronous forced oscillation and damping evaluation are carried out based on transient energy flow. The computation formula of transient energy flow for subsynchronous analysis is studied. To compute transient energy flow

instantaneous voltage and current of component ports in abc axis are converted to xy axis. The composition of transient energy flow in a detailed generator model with multi-mass torsional shaft is derived

which is transient energy and dissipated energy by damping. This explains the relationship between energy flow and damping. The positive value of the power of energy flow injected into a component represents energy dissipation. The component is considered possessing positive damping if it absorbs energy. In subsynchronous forced oscillation

as the disturbance source steadily generates energy

the source of disturbance can be located by calculating the oscillation energy flow and energy flow power in the network. Different test cases are built and simulated under electromagnetic transient simulation software. The validity of the method is verified by the simulation results. This work is supported by National Natural Science Foundation of China(No. 51377002)and State Grid Corporation of China(No. 5201011400M5).