Fault Analysis in LVDC Systems: Accuracy and Applicability of the Traditional Method

A systematic and responsible expansion of Low Voltage DC systems demands a thorough understanding of specific aspects of DC systems, such as protection systems, DC grids response to a fault, and fault identification and clearance, which are currently limiting the spread of DC distribution systems. For a preliminary evaluation the Traditional DC Fault Analysis method can be a useful tool for estimating fault current contributions from DC converters in LVDC networks during a fault. Unfortunately, its accuracy decreases when considering systems with multiple converters and non-negligible fault impedance. This limitation stems from the inherent assumptions in the analytical solution, resulting in: a) dependence on the reliability of results on fault impedance values and/or contributions from all fault currents of the other converters connected to the DC grid; b) inaccuracies of diode currents estimation, and c) inaccuracies in the Joule integral evaluation. These results may prove unreliable for designing protection systems for either a single converter or an entire network. Consequently, the aim of this work is to clearly identify these limits and to define Traditional DC Fault Analysis applicability in a complex network.