Wide area protection and emergency control

This paper describes basic principles and philosophy for wide area protection schemes, also known as remedial action schemes (RAS) or system protection schemes (SPS). In the areas of power system automation and substation automation, there are two parallel trends in different directions: centralization and decentralization. More and more functions are moved from local and regional control centers towards the central or national control center. At the same time we also observe more and more "intelligence" and "decision-power" moving closer towards the actual power system process. We also see a great deal of functional integration, i.e., more and more functionality enclosed in the same hardware. This raises discussions concerning reliability (security and dependability). The main targets for this paper is therefore to:sort out the terminology used in this area; Describe different application areas and related requirements; illustrate different design principles - "top-down", "bottom-up", hierarchy, flat, etc., for different applications; and identify similarities and differences between classic equipment protection and system protection concerning philosophy as well as concerning product and system design.