Accurate Measurement of Fault Currents Contaminated With Decaying DC Offset and CT Saturation

Decaying dc offset and current-transformer (CT) saturation are the main obstacles to accurate measurement of the fundamental frequency component of fault currents. So far, most of the research works have focused exclusively on only one of these obstacles. However, very recently, research has been directed toward new current measurement algorithms which can deal with both of these issues simultaneously. Using least error squares technique and a simple offline lookup table, this paper introduces a novel method to filter out the decaying dc component and the effects of CT saturation. The proposed algorithm provides the fundamental sinusoidal component of current accurately. This method can respond using only five current samples. Meanwhile, the window size could also be increased to provide more immunity against noise and harmonics. High speed and accuracy, together with the simplicity and noise immunity of the proposed method, can make it a practical solution to address the decaying dc offset and CT saturation problems. Numerous simulated and real fault currents as well as real-time hardware implementation verify the effectiveness of the proposed algorithm.