Possibility of phasor estimation in digital relays without using anti-aliasing filter and very high sampling rates

Abstract

In digital relays, anti-aliasing filters introduce additional time-delays in the phasor estimations. This time-delay reduces the speed of the protection relay. Removal of anti-aliasing filter from digital relay is beneficial from the point of view of cost, compactness, power dissipation, reliability and maintainability. Previously efforts have been made to remove anti-aliasing filter from digital relays using very high sampling rates. However, existing digital relays do not support very high sampling rates. The purpose of this paper is to investigate the possibility of phasor estimation without using anti-aliasing filter and very high sampling rates. Compressive Sampling (CS) theory has opened up a new possibility of signal reconstruction from sub-Nyquist rate samples. This paper proposes a CS based phasor estimation method for digital relays. The proposed method can work with the lower A/D sampling rates. The performance of the proposed method has been evaluated using signals generated by PSCAD software and mathematical equations. It is shown that the proposed phasor estimation method has faster response than the conventional approach. Results show that the frequency specification of anti-aliasing filter can be significantly relaxed in the proposed method. The complete removal of anti-aliasing filter is also possible at the cost of significant computational burden. In summary, this paper presents some promising results regarding removal of antialiasing filter from digital relays with lower sampling rates.