Sequence currents based adaptive protection approach for DNs with distributed energy resources

Abstract

In this study, sequence currents based adaptive directional overcurrent relaying approach for distribution networks (DNs) with distributed energy resources (DERs) is proposed. Owing to the grid-connected mode and islanded mode operations, the magnitude and direction of fault currents are altered. Such different modes of operation result in protection failure and loss of coordination between directional overcurrent relays (DOCRs). With inception of faults, the current contributed by the inverter-based DER is in the range of 2 pu. Protection coordination is achieved by the adapting relay settings for each operating mode of DERs using the stored conventional relay settings, and the protection coordination is further improved by using negative-sequence overcurrent-based backup DOCR. The direction of the fault is obtained using the phase change in superimposed and prefault positive-sequence currents. The proposed technique is implemented on a dSPACE processor, which is connected to a real-time digital simulator to carry out the hardware-in-the-loop test. Extensive simulation and hardware results obtained for several DN operating modes. The adaptive approach is compared with the conventional approach and results indicate that the adaptive approach provides accurate operating time for primary and backup relays. This proposed approach is independent of the voltage information.