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A current signal often exhibits dynamic characteristics and contains decaying dc components when an earth fault occurs under power oscillations. In this paper, a dynamic phasor estimator for fault current (DPEFC) is proposed to remove the phasor-estimation errors caused by dynamic characteristics and decaying dc components. The proposed DPEEC estimates dynamic characteristics and decaying dc components accurately by an iterative procedure. It can also eliminate the impacts on phasor estimation by reassigning estimations from discrete Fourier transform with the knowledge of the fundamental phasor and the dc components. The performance of the proposed DPEFC is evaluated by computer-simulated signals and EMTDC-generated signals. The results indicate that DPEFC can achieve accurate phasor estimation of fault current in the presence of dynamic characteristics and decaying dc components with a minimal increase of computational cost which meets the requirements of the application in phasor measurement units.
Date of Publication: July 2011