Capacitive earthing charge-based method for locating faults within a DC microgrid

Abstract

This paper presents a new fault location method using capacitive earthing charge current combined with moving average and Savitzky-Golay filters. Locating a DC fault in a DC microgrid can be challenging due to reduced fault current magnitudes, resulting either from high resistive faults, or during the transition between grid-connected and islanded modes. The capacitive earthing method is proposed for earthing DC systems to avoid the corrosion of earthed metallic surfaces. Under different fault conditions and at different locations, the capacitive earthing with the earth path, charges a transient current with a peak value that depends on the initial voltage of the capacitor and the fault loop between the capacitor and the fault point. Therefore, this paper utilises earth capacitor pre-fault voltages, transient current peak and the derivative current of the capacitive earthing to estimate the total inductance of the fault loop. This in turn can be used to determine the location of DC faults. This paper also quantifies the impact that resistive faults have on the accuracy of the method, especially when the resistance of the fault dominates the total fault loop. The ability to distinguish between downstream and upstream faults with respect to the earthing point location also adds significant value to the proposed method. The proposed fault location technique is tested against pole-to-earth fault at different locations using Matlab-Simulink.