Strong DC coupling with weak AC and large-scale renewable energy integration are the two significant characteristics of ultra-high-voltage AC/DC (UHVAC/DC) hybrid power grids in China. Strong coupling between AC and DC grids and the different integration performance of renewable energy sources have profoundly changed the stability characteristics of the power system. The traditional stability control system is inadequate for the stability control of UHVAC/DC power grids. This paper analyzes the requirements for constructing an integrated defense system in a UHVAC/DC hybrid power grid (i.e. power system protection). The definition

connotation

and designing principles of power system protection are put forward. The relationship between the power system protection and the traditional three-defense lines is investigated. The design principles

general hardware structure and main functions of a power system protection are presented. Key problems and technologies are specified in the construction of the power system protection.