Assessment of a decaying DC offset detector on CTs measurements applying mathematical morphology

Power system protections are highly sensitive to decaying dc offset that could appear when a fault occurs. The consequences of this effect represent a challenge in the coordination of protection devices that have been widely studied. The elimination of the dc offset component of current transformers (CTs) measurements is the objective of this paper, including a new autonomous detector based on mathematical morphology. The idea enhances the digital signal processing to prepare the information before the protective device takes a decision. The detection and fast elimination of the decaying dc offset on current signals could improve the speed of protection, coordination, and selectivity. The paper presents the proposed algorithm and assesses the solution using alternative transient program. The model of the CT used for this validation is also presented. Results show the potential of the mathematical morphology for signal processing to delete the dc offset component.