The transient energy flow method is a new method of oscillation analysis

which can be applied to the oscillation source location and damping assessment. This paper further studies its physical significance in subsynchronous oscillation. The relationship between transient energy flow

subsynchronous power and supersynchronous power is deduced. The power of energy flow is proportional to the difference between supersynchronous power and subsynchronous power. In a subsynchronous resonant system with series compensation equipment

the resistance may consume or generate transient energy

which is negative damping when the transient energy is generated. The inductance and capacitance are zero damping

but can greatly affect the damping characteristics of resistance by changing the line current. By comparing transient energy flow with the damping torque coefficient of the electrical subsystem

the rationality of above derivation is verified. Finally

the simulation results in different examples verify the validity of the conclusions.