Performance of Shipboard Medium-Voltage DC System of Various Grounding Modes Under Monopole Ground Fault

This paper compares different grounding modes of a shipboard medium-voltage dc (MVDC) system such as ungrounded, solidly grounded, grounded with resistors, and grounded with resistors in parallel. Based on a typical shipboard MVDC system under different grounding modes, the transient short-circuit current and overvoltage under a monopole ground fault condition are calculated with PSCAD/EMTDC. The impact of the grounding resistance on the fault feature of the system is also studied. According to the comparative analysis and simulation results, a suitable grounding mode and the grounding resistance are proposed. The influences of load conditions, capacitance of loads, capacitance of the transmission cables, resistance between line and ground at the fault point, and fault position on the overvoltage are considered. Finally, a system protection scheme consisting of grounding mode selection, capacitor, arrester, and conjugate mirror filter has been developed.