LVDC Networks Fault Analysis for Protection Devices Selection

Protection devices play a crucial role in safeguarding LVDC grids, and their characteristics are strongly related to the grid design. Recently, significant emphasis has been placed on the design and selection of protective devices suitable for active DC grids. Depending on the technology used, protection devices have different breaking characteristics, impacting the power dissipated during a fault and thereby the sizing requirements of the different grid components. However, to achieve these outcomes, it is firstly necessary to accurately evaluate the DC grid fault current and voltage in any point in the grid and in different fault conditions. A preliminary estimation of fault current contributions can be addressed by the traditional DC fault analysis method only when the DC grids are simple and with few converters and/or for bolted faults because its accuracy significantly decreases when these conditions are not verified. As a result, a more accurate and flexible method to evaluate current and voltage with no restrictions on grid complexity or fault type would be highly beneficial, especially in the case of multiple converters and/or nonnegligible fault impedance. This paper discusses an innovative strategy for protection device selection in a generic LVDC grid. In particular, considering the different available technologies for DC circuit breakers, the main variables that can be used to trip protection devices are highlighted, and the effect of different technologies and settings on clearance times and relevant grid variables are discussed.