Current differential protection method for unipolar ground fault of DC distribution network based on current variation characteristics

When a DC distribution network with a small current ground is protected by existing current differential protection methods, The anti-transition resistance and anti-noise ability of this method are poor, and it is easily affected by the capacitor current distributed by the line. Therefore, a unipolar ground current differential protection method based on current variation characteristics of DC distribution network is proposed. When unipolar grounding, the current flow loop and charge-discharge characteristics of the line distributed capacitance are analyzed. In the event of a fault in or outside the zone, the difference in the components of the positive and negative differential currents across the protected area is obtained. The characteristic quantity of variation is introduced to characterize the degree of variation of the differential current. In addition, the ratio of the variable feature quantity and the variant feature quantity in the protected area is coordinated in two stages, and the protection criterion threshold is adjusted. For simulation verification, a two-terminal flexible DC distribution network model was constructed using the PSCAD/EMTDC simulation platform. The findings demonstrate that the suggested approach is capable of precisely locating the fault region and won't lead to incorrect conclusions owing to the impact of capacitor current dispersed by DC line. And it has good anti-noise and anti-transition resistance ability.