An analytical approach for removal of decaying DC component considering frequency deviation

• The proposed method is the decaying DC component removal algorithms with regard to frequency deviations. In this approach the effect of decaying DC component created by CT is considered.
• TThe nature of the proposed algorithm is based on Hilbert transform and periodic integration, which causes harmonic elimination.
• These two above-mentioned points can cause analog low pass filter removing in numerical relays, which result in relay size reduction and speed up relay decision making.

Decaying DC component has an important effect on extracting the fundamental phasor. It directly affects the precision of protective relaying algorithms which act based on the fundamental frequency component. Generally there are two DC offsets in a CT secondary signal, which are estimated and their effects will be eliminated in first cycle data window. This paper proposes an analytical hybrid approach for fundamental phasor estimation in order to remove the decaying DC components using Hilbert Transform (HT) and Discrete Fourier Transform (DFT). The proposed method converges to the original value in one cycle in presence of harmonics. In addition, the proposed algorithm is able to detect the frequency fluctuation. Thus, it is applicable for static and dynamic conditions. Simulation results represent that the proposed method for estimating phasor achieves robust performance in comparison with conventional DFT method.