A novel method for removing the decaying DC component in digital relays

One of the major duties of digital relaying is the accurate estimation of fundamental frequency and its phasor. Digital relays usually use discrete Fourier transform to estimate the fundamental frequency harmonic, but decaying DC component is a great challenge to achieve this goal when a fault occurs. This paper presents a new integral-based method to remove the DC offset from current signal. The proposed method uses only half of the sampled data per cycle plus one sample to appraise time constant and magnitude of the DC offset. Then, by subtracting value of the decaying DC component at each sample, DC-removed signal can be achieved. The performance of the proposed technique is evaluated by computer-based signals and signals generated by EMTP. The results illustrate appropriate operation of the suggested algorithm in removing the decaying DC component.