The element of flexible AC transmission system（FACTS）devices

after fault of system

maybe out of operation

its reoperation has big influence on the system stability and the influence at different operation is difficult. In this paper

the mechanism of optimal switching of FACTS element is analyzed

a transient kinetic energy function of two-machine system is established to calculate optimal switching time of FACTS devices based on extended equal area criterion（EEAC）. A new method based on the measurements of wide area measurement system（WAMS）to calculate optimal switching time of FACTS devices is proposed. Finally

the STATCOM is taken as an example

the two zone four generator system models are built by way of PSCAD/EMTDC platform. The simulation results show that the switching FACTS element at optimal time can calm down effectively swing of power angle of generator and power oscillation in tie line as well as improve system stability.