New Algorithms for Removal of DC Offset and Subsynchronous Resonance terms in the Current and Voltage Signals under Fault Conditions

Two filtering algorithms for removal of DC offset and subsynchronous resonance terms in the current/voltage signals in a transmission line under fault condition are presented. One of the algorithms utilizes the samples of the signal over a time interval slightly greater than one cycle time of the fundamental component and is computationally less demanding than the existing Fourier filters. The second algorithm is based on sampling the signal at arbitrary locations and hence, the signal samples can be acquired during a time interval much less than the full-cycle period of the fundamental component. This results in the calculation of the fundamental component in a time less than the full-cycle time of the signal, and hence is more attractive. It is shown that the Fourier filters used for the removal of DC offset etc. can also be interpreted as the weighted moving-average filters. Moreover, the Fourier filters, although having similarity with the discrete Fourier transform (DFT) computation of a signal, do not precisely involve the computation of the DFT coefficients of the sliding windowed sampled signal. Lastly, simulation results are presented to validate the approach of both the proposed algorithms under noiseless as well as noisy conditions. Key-Words: -Discrete Fourier transform, Power system protection, Power system transients, Power transmission lines