A Coordination Scheme for a Combined Protection System Considering Dynamic Behavior and Wind DGs Fault Ride-Through Constraints

A combined protection system has multiple types of devices such as directional overcurrent relays, reclosers, and fuses to protect distinct areas in a DG-incorporated network. An approach for setting all protective devices to realize complete coordination of adjacent ones taking transient responses into account is presented. The participation of synchronous generator-based and/or inverter-based wind DGs can degrade protection coordi-nation. So, a scheme for sustaining coordination by optimal hybrid superconducting fault current limiters is proposed. The scheme can cope with variation of network topology; and handles the change of fault current level perceived by the protection device under a given topology. Moreover, instead of the conventional steady-state models, more realistic dynamic models of relays, reclosers, DGs, and fault current limiter are used. As a serious operation problem, undesired tripping of wind DGs under fault condition can occur due to the sag of terminal voltage below certain limits defined by national and international standards. Therefore, the proposed scheme prevents this undesired tripping of wind DGs by integrating its ride-through capability constraints into the fault current limiter allocation problem. The proposed approach is applied to the IEEE 9-bus and 30-bus systems. Results confirm the efficacy of the proposed method.