An adaptive distance relay protection scheme for enhanced protection security

The advantage of distance relay to provide remote backup protection is a matter of concern to power system security under system stressed conditions. The zone 3 of the distance relay is prone to mal-operate under well known system stresses such as power swing, load encroachment and voltage stress; causing undesired relay operation which may further lead to system collapse. This paper proposes an adaptive distance protection scheme based on the decomposition of the current and voltage signals into carrier signals and modulating signals using the amplitude demodulation technique. The magnitudes of the carrier signals are controlled adaptively by a magnitude monitoring function based on the information content in the modulating signal. During power system stressed conditions, the positive sequence impedance trajectory is restrained from entering the distance relay trip zones until a fault occurs on the system. The proposed algorithm is tested on a two area - 4 generator - 10 bus system modeled in ATP-EMTP environment and the simulation results show the reliability of the scheme.