Improvement of Phasor Estimation Accuracy by Prony-based Identification of Two Decaying DC Components

During transmission line faults, a sampled current signal can contain two decaying dc components (DDCs). A primary DDC develops on the faulted transmission line and a secondary DDC arises at a current transformer of the numerical relay. Currently, most numerical relays are designed to remove a phasor estimation error due to the primary DDC in ignorance of the secondary DDC. Their protection performances can be enhanced by correcting an error of phasor estimation due to the secondary DDC. In this paper, a full-cycle discrete Fourier transform (FCDFT)-based phasor estimation method with identification of the primary and secondary DDCs is proposed to improve the phasor estimation accuracy. Prony analysis is applied to the identification of the two DDCs. To alleviate the noise effect in Prony analysis, the identification of the two DDCs is performed on two types of FCDFT coefficients at the quarter and half sampling frequencies. The feasibility of the proposed method is demonstrated in simulations on the DDCs and noise, and a faulted transmission line.