Sustained Coordination of Devices in a Two-Layer Protection Scheme for DGs-Integrated Distribution Network Considering System Dynamics

Distribution networks are usually protected by directional overcurrent relays (DOCRs). Besides, autoreclosers and fuses can be used for protecting lateral feeders to minimize power cuts. Coordinated operation of protection device must be maintained to ensure optimal fault isolation. Typically, steady-state fault current and static protective device characteristics are used to determine optimal settings of devices such that coordinated operation is verified. Sine fault current is not a steady signal and protection devices have dynamic behaviors, the conventionally-determined settings of devices can lead to loss of coordination jeopardizing system reliability. In this paper, a two-layer protection scheme is proposed for a distribution network with distributed generators (DGs). The first layer has DOCRs to protect main feeders. The second has autoreclosers and fuses to protect lateral feeders. Optimal settings of devices are determined to achieve both local-layer and inter-layer coordination of devices by constrained nonlinear optimization. Full dynamic models of every component and transient data of fault current are considered. Furthermore, to sustain coordination under DGs, a hybrid superconducting fault current limiter (HSFCL) with high temperature superconducting resistive element is connected in series to each DG. Dynamic modeling-based HSFCL cost minimization is searched by multi-objective optimization. The approach is applied to two distribution networks and simulation results are analyzed.