A composite index to adaptively perform fault detection, classification, and direction discrimination for transmission lines

This paper presents an adaptive protection scheme for transmission lines based on synchronized phasor measurements. The work includes: fault detection, fault classification, and fault direction discrimination. Using two-terminal synchronized measurements incorporated with distributed line model and Clarke transformation theory, fault detection index is derived. We can classify the faults by the proposed modal fault detection index and the circuit breaker can achieve single-pole tripping. The fault detection index is composed of two complex phasors. The fault events can be found according to the angle difference between these two phasors as in internal and external fault situation. The proposed method also combines on-line parameter estimation to assure protection scheme performance and to achieve adaptive protection. After a lot of EMTP simulations and verifications show that the method provides a fast and accurate protection scheme for transmission lines. The tripping decision time of the protective relay is within 1/2 cycle.