In order to study the necessity and specification requirements of static var generator (SVG) dynamic reactive power compensation applied in large-scale grid connected wind power plant and photovoltaic substation, this paper comparatively studies the two kinds of reactive power compensation, i.e. static var compensator and static var generator, in terms of regulation characteristics, response speed and other performance indicators. For grid connected new energy projects in Gansu Province, it analyzes some details and misunderstandings about reactive power configuration and reactive power device operating experience of wind power plant. And it researches voltage support and reactive power of SVG to power system under grid failure condition, combined with analysis of typical accident case. Meanwhile, SVG selection, typical wiring program and common failure problems of centralized grid-connected photovoltaic substation in practical engineering applications are studied, which is benefit to similar projects.