y and economically The capital investment involved in power system for the generation, transmission and distribution is so great that the proper precautions must be taken to ensure that the equipment not only operates as nearly as possible to peak efficiency, but also must be protected from accidents The normal path of the electric current is from the power source through copper (or aluminium) conductors in generators, transformers and transmission lines to the load and it is confined to this path by insulation. Nature of Faults  Short circuit fault- current  Open circuit fault- voltage In terms of seriousness of consequences of a fault, short circuits are of far greater concern than open circuits, although some open circuits present some potential hazards to personnel Classification of short circuited Faults • Three phase faults (with or without earth connection) • Two phase faults (with or without earth connection) • Single phase to earth faults Classification of Open Circuit Faults • Single Phase open Circuit • Two phase open circuit • Three phase open circuit