Data window selection for removal of decaying DC component in current phasor estimation for distance protection

In distance protection, the fault current signal is usually distorted by the decaying direct current (DC) and harmonics preventing accurate and fast estimation of the fault current phasor. This paper presents a method based on the carefully selected data windows and least square (LSQ) method to improve the performance of the current phasor estimation. The method comprises a short and variable data window for fast operation of distance relay for close faults and a fixed data window for the accurate operation of the relay for faults close to the boundary of Zone 1. The short and variable data window can achieve high speed in the phasor estimation in a quarter of cycle, whereas the second algorithm uses a fixed data window with an excellent frequency response to increase the accuracy of the phasor estimation. The proposed method is first tested using mathematical formulation under different conditions such as different characteristics of the DC component, noise, harmonics and frequency deviation. Then the method is tested by more realistic samples taken from a simulated transmission system under different fault conditions for flexibility, speed and accuracy. All the test results validate the aforementioned features of the proposed algorithms.