A Novel Adaptive Relaying Scheme for Distribution Networks with DG by considering Fault Severities

The power distribution networks are radially structured, with fuses, reclosures for temporary faults, and relays. After the connection of Distributed Generation (DG) to the power system, it is subject to the in-feed effect which results in different currents flowing through primary and backup relays. Thus, predefined coordination time interval (CTI) will be changed, which in turn, leads to the violence of coordination rule between the relays. This paper proposes a novel adaptive protection scheme for the power network integrated with DG which takes the severity of the fault current into account. Thus, the higher the magnitude of the fault current, the faster will be the breaker action and fault isolation. The solution is to adjust the variable relay parameters including Time Dial Setting (TDS) and Plug Setting (PS) of Inverse Definite Minimum Time (IDMT) relays. According to the proposed algorithm, the relay settings are updated based on the status of the breaker connected to the DG. The paper implemented IEEE 33-bus power distribution network to analyze the influence of DG on the operations of primary and backup relays and to test the proposed algorithm. The simulation results showed that the proposed scheme is effective in maintaining CTI in distribution systems with PV involvement.