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Protection of a power system is an extremely important aspect as the duality and scheme of protection decides system reliability, controllability and stability. This paper concentrates on the protection of a distribution system in the light of developments in distributed generation (DG). The conventional distribution system is radial in nature, characterized by a single source feeding a network of down-stream feeders. The protection system has traditionally been designed assuming the system to be radial. After connecting DG, part of the system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination will depend on size, type and placement of DG. This paper explores the effect of DG on protective device coordination such as fuse-fuse, fuse-recloser and relay-relay. In each case, depending on size and placement of DG, there are some margins in which the coordination may hold and certain cases, where no margin is available. These conditions are identified for each case through coordination graphs.
Girgis et al. (Wed,) studied this question.