Investigation of Adaptive Auto-Reclosing for Radial Distribution System with Distributed Energy Resources

Abstract

DERs (distributed energy resources) recently have gained popularity in electrical distribution systems. The interconnection of DERs to RDS (radial distribution systems) introduces challenges to the protection and control system of the RDS. Bidirectional current flow is introduced to the RDS due to the interconnection of DERs at load side. In this case, the conventional protection scheme might fail to maintain the proper level of security and dependability. The majority of faults in RDS are temporary in nature and require the auto-reclosing scheme to reduce the impact of such faults. Connecting two live electrical systems requires proper synchronization to avoid mechanical damage to generators. This thesis investigates an approach to have adaptive auto-reclosing in RDS with interconnected DERs. The approach is based on zonal directional overcurrent protection, which utilizes the overcurrent condition with the current directions to determine the faulty zone. The approach suggests tripping DERs connected to the faulty zone and limiting the auto-reclosing to the zonal breaker closer to the grid substation. Doing this, the synchronization requirements are avoided as reclosing is performed to a de-energized zone. Also, the adaptive approach adjusts the TDS (time dial setting) of the recloser fast curve to re-establish coordination with fuses in the zone. Due to the interconnection of DERs, fuse and recloser might see different fault currents, which might cause miscoordination. The adaptive approach allows the implementation of “Fuse Saving” scheme, which is usually desired in RDS.

The suggested approach in this thesis was implemented on PSCAD™/EMTDC™ applied to a test system. The test system is a modified dual IEEE 34 node distribution test feeder with interconnected DERs. The behavior of the approach was investigated by simulating various faults types at different locations on the test system. The approach for the zonal breaker was successful in identifying the right breaker to perform the auto-reclosing following the right sequence. The adaptive approach was also successful in restoring the fuse-recloser sequence of operation. The fuse saving scheme operation sequence was sustained as well. However, the minimum coordination margin between the fuse and the recloser was not maintained properly for most of the case studies.