This series of papers report on relay protection strategies that satisfy the demands of a strong smart grid. These strategies include ultra-high-speed transient-based fault discrimination

new co-ordination principles of main and back-up protection to suit the diversification of the power network

optimal co-ordination between relay protection and auto-reclosure to enhance robustness of the power network. There are also new development in protection early warning and tripping functions of protection based on wide area information. In this paper the principles

algorithms and techniques of single-ended

transient-based and ultra-high-speed protection for EHV transmission lines

buses

DC transmission lines and faulty line selection for non-solid earthed networks are presented. Tests show that the methods presented can determine fault characteristics with ultrahigh- speed (5 ms) and that the new principles of fault discrimination can satisfy the demand of EHV systems within a smart grid.