Single Dual Setting Directional Over-current Relay Based Line Protection Logic for Distributed Generation Integrated Power Systems

These days, the concept of distributed generations is being widely adopted due to the increased interest in the smart grid and its applications. The integration of distributed generators (DGs) resulted in the transformation of the distribution networks topology from radial to the looped/meshed networks. However, the addition of DGs not only alters the magnitude of fault current but it also results in bi-directional power flow. Thus, the line protection in a DG based power system is mainly based on the directional overcurrent relays (DOCRs) to address the issue of bi-directional power flow. With the technological advancement, the conventional DOCRs are now being replaced by the multi-functional digital relays. This makes it possible to use dual setting DOCRs. In this study, the combined deployment of conventional and dual setting DOCRs is investigated to decrease the number of relays and current transformers (CTs) used for line protection in the IEEE 14 bus distribution system. Since a single dual setting DOCR can have two different tripping curves for forward and backward current directions, the number of costly DOCRs can be reduced compared to the conventional line protection system. To analyze the applicability of the replacement, the proposed protection logic is simulated in the Electrical Transient and Analysis Program (ETAP). Three cases are considered in the simulation. Since, relays and CTs are expensive protection devices, reducing the number of relays and CTs without compromising the level of protection will provide a cost-effective protection solution.