Simulation of Elliptical Relay for Long Transmission Line Protection using MATLAB Software

Relays are a key device for protection of transmission lines. It isolates the faulty section of electrical power system from rest of the power system so that the rest portion can function satisfactorily without any severe damage due to fault current. Power swings occur frequently in long transmission lines. Hence for protection of long transmission line, a relay must be chosen so that it is least affected by power swing. Also relay must operate fast to prevent damage and maintain the stability of the system. In classical relay systems, the trip signal is generated after at least one AC cycle. Elliptical relay is least affected by power swings. The algorithm used for the generation of trip signal in proposed method operates the relay within one AC cycle which is much faster than a classical relay system. The simulation results are obtained for both classical relay and the relay system using this algorithm in MATLAB software. This paper presents the modelling of elliptical relay using the classical algorithm and the proposed algorithm in MATLAB software. The conic characteristics are simulated and results are verified in MATLAB software.