Principle and Implementation of Current Differential Protection in Distribution Networks With High Penetration of DGs

With the high penetration of distributed generations (DGs), the conventional radial distribution network is becoming an active distribution network (ADN). It has the characteristics of multisource, multibranch, bidirectional power and fault current flow, as well as weak infeed. To provide effective protection for such a network, a novel current differential protection scheme, together with new implementation technology, is proposed in this paper. In this scheme, instead of using phase currents, a positive-sequence fault component (PSFC) is introduced into the differential protection. By building the PSFC equivalent circuit of the ADN, the distribution characteristic of PSFC within the ADN is theoretically analyzed in detail, especially for the case when the ADN contains inverter interfaced DGs. The PSFC-based differential protection criteria for different types of feeder are then established and simulated. To put the scheme into practice, data self-synchronization and peer-to-peer communication techniques are established. Based on this principle and using an advanced hardware platform, a protection prototype is successfully developed and tested. The test results verify the feasibility of the proposed protection scheme.