Applications and limitations of the inverse-time overload relay to the protection of an 11-kV network

Methods of grading overload inverse-time relays, with definite minimum time, on an 11-kV system are discussed with special reference to the reduction of tripping times throughout, especially at the source of supply. A method is developed which attains this object and allows a large number of relays to be used in series. A system of recording network short-circuit calculations and emergency relay settings is also discussed.