Most protection algorithms including distance protection algorithms use the phasor of the fundamental frequency component of voltage and current signals. To extract the fundamental frequency component of voltage and current signals, digital filters such as filters based on discrete Fourier transform (DFT) and filters based on the least square (LS) method are used. When a short circuit fault occurs, the fault current contains a decaying DC component, which can adversely affect the permanent and transient performance of digital filters and, as a result, the performance of protection algorithms. In this thesis, introducing Fourier and least square digital filters, the effect of the decaying DC component (DDC) on the performance of these algorithms has been investigated based on different methods and criteria. Specifically, full-cycle Fourier, half-cycle Fourier, cosine and least square filters based on the considering different content for the fault signal model are introduced and their permanent and transient performance in the presence of the decaying DC component has been investigated. Also, the methods introduced to improve the performance of aforementioned filters in the presence of the decaying DC component are reviewed and eva‎luated.

محمداسماعيل همداني گلشن

محسن حمزه , فاطمه زارع