Proteção diferencial de transformadores de potência baseada na corrente de sequência negativa

Abstract

The present thesis proposes a new power transformers differential protection algorithm based on the negative sequence current, which is reconstructed in time from the corresponding phasor at both transformer windings. Aiming to provide a faster and more reliable operation of the proposed method, the ratio of the operating and restraint negative sequence current signals is integrated during the time. The proposed method also incorporates a function that detects disturbances nearby the transformer, and a new harmonic restraint strategy is also proposed, to improve protection security for external faults with current transformer (CT) saturation. In order to evaluate the performance of the proposed algorithm, a wide variety of disturbances is simulated in the software Alternative Transients Program (ATP): external short-circuits, CT saturation, transformer nearby external fault removal, sympathetic inrush condition and internal faults, by varying the fault type, short-circuited turns percentage, sources strength and the power system loading. In addition, it was performed comparative evaluation between the proposed differential protection and the current traditional differential protection (based on the phase and negative sequence elements). Finally, the proposed algorithm logic was implemented in a commercial differential protection relay, allowing its experimental validation. The obtained results reveal that the proposed method is able to detect turn-to-turn and turn-to-ground faults, even for 1% of short-circuited turns, so that it can be a complement to the phase differential functions, for a faster and more sensitive operations for internal faults involving few turns, and safe for external short-circuits with CT saturation.