Modern applications of line differential protections to improve EHV transmission grids security: the Italian experience

EHV transmission grids require more and more a fast and selective fault clearing in order to guarantee the requested levels of security and stability. In last years, technology has made available new line devices with embedded differential and distance protection functionalities (87L/21). These multifunction devices include also some other enhanced features. Moreover, the increased availability of suitable telecommunication vectors (fiber optic, SDH networks, MPLS networks, etc.) has enabled their diffusion and use. In the first part of the paper, the main advantages of line differential protection use for selective clearing of different fault types are described and its performances are compared with distance protection ones. In the second part Terna's approach and experience on line differential protection installation and future spread plans are reported. There are also described telecommunication approaches already in use (Fiber Optic, SDH networks) and the current tests on advanced MPLS networks usage. In the final part some future perspectives on Sampled Value IEDs and traveling wave-based protection schemes are briefly introduced.