Keywords: spline function, fault clearing security factor, FCSF, adaptive relaying, maximum fault clearing time, MFCT, in-feed ratio, overcurrent grading, multifeed distribution systems, overcurrent relays, power systems
Spline function-based adaptive overcurrent grading for multifeed distribution systems
In spite of the changes in the hardware and the principle of operation, the characteristic of the overcurrent relays has not undergone much change. The scheme proposed in this paper is based on the spline function characteristic rather than the conventional overcurrent characteristic and is adaptive in nature. Also, the fault clearing time for each fault current level is based on system fault washstand level. The concept is proposed for a system that has four buses forming a ring and each bus has a generator connected to it. One of the relays has two characteristics and is provided with automatic selection of the characteristics and this way adaptability is built in the system. This scheme is easy to implement using a numerical relay and utilises the capability of the numerical relays in a better way.