A moving average smoother to improve the accuracy of impedance based protection

Abstract

Traditional protective relays work based on a frequency domain since many decades ago. Over the last decades, the fundamentals of a Discrete Fourier Transform (DFT) have shown fair performance when computing the signals before entering a protection algorithm. However, modern power systems integrate complex elements that may affect the response of a trip under particular faults. This research addresses the problem of the phasor computing of a traditional relay. The problem is identified specifically with the selectivity and the accuracy of zone detection for an impedance based protection. A novel moving average module is proposed and assessed with playback simulation and further development of a prototype in a Digital Signal Processor (DSP) for the industrial development of relays. The contribution is focused on the better accuracy of zone detection, including higher selectivity with a low impact on the protection speed.