In a thermal power-renewable energy combined transmission system

the transient power rotor angle instability of thermal power units and the transient over-voltage at the renewable energy generator terminals are important issues that limit the transmission capacity. First

an analytical equation for the power rotor angle variation of thermal power units considering the negative impedance characteristics of new energy is established

and the new transient power rotor angle stability characteristics of thermal power units after the integration of new energy are analyzed. Secondly

based on the Thévenin equivalent and vector analysis method

the transient over-voltage at the new energy machine terminal is analyzed

and the influencing factors of transient over-voltage are discussed. Next

through formula analysis and electromagnetic transient simulations

the coupling relationship between two types of transient over-voltages is highlighted. Finally

using a practical engineering case as an example

this study analyzes the dominant risk modes under different scenarios

and proposes operational modes under two integrated risk constraints. The research results provide technical references for the safe and stable operation of thermal power-renewable energy combined energy bases in the new situation.