Fault detection and location in medium‐voltage DC microgrids using travelling‐wave reflections

Abstract

Fast dc fault detection method is required in medium-voltage dc (MVDC) microgrids to avoid severe damage to the interfacing converters. Ensuring selectivity and sensitivity of the protection system within a few milliseconds is a major challenge. This study proposes a new technique based on fault launched travelling-waves (TWs) to detect, classify, and locate different dc fault types in MVDC microgrids. Unlike the existing TW-based protection and fault location methods, the proposed technique utilises the frequency of TW reflections, rather than their arrival time. Moreover, the fault initiated voltage TW is contained within the faulted line by adding smoothing inductors on line terminals, which (i) prevents relays on adjacent lines from detecting the TW and (ii) results in higher reflected TW magnitudes. Therefore, the proposed method's selectivity and sensitivity are enhanced compared to existing methods. Other salient features of the proposed scheme include a moderate sampling frequency of 2 MHz, detection speed of 128 μs, fault location accuracy of ±25 m, no communication requirement, and independence from system configuration. The proposed scheme's performance has been assessed using a ±2.5 kV TN-S grounded MVDC microgrid under various conditions. The fault location accuracy of the proposed technique is compared to the conventional single-terminal TW-based method.