New theory of directional current protection for the distribution network containing DG based on fault component

The distribution network will be changed from the single power to the multi-power supplied when DG combined into it. Three-section current protections will no longer be applicable. Therefore, a new protection scheme which is suitable for the distribution network contained DG be proposed, which is that the protections lying on the downstream lines of DG need to have new setting value, and the protections with the directional components need to be installed on the line between the power and DG. Based on the qualitative analysis of the influence of DG combined into the network on the traditional current protection of distribution network, this paper proposed a new directional current protection on the basis of the positive- sequence fault component. The scheme using fault component principle analyzed the phase angle difference of the positive- sequence current in one period just before the fault and that just after the fault, worked out the protection criterion of the positive and negative fault, and thereby realized the fault location.