Thesis (Ph.D.) - Cairo University - Faculty of Engineering - Department of Electrical Power and Machines

The integration of distributed generation to the distribution networks and the wide application of microgrid concept to the existing distribution networks lead to challenges for protection schemes due to bidirectional power flows, unintentional islanding, and the change in short circuit level during different modes of operation or the change in network operating conditions.This thesis proposes three protection strategies to deal with the distribution network and microgrid protective schemes.The first proposed strategy is a new islanding detection technique based on the production of voltage sequence components at every relay location not only at the DG point of common coupling.Thus, detecting the islanding at all relays provides updating the protection setting for all relays based on local measurement only without need for a communication network. The second strategy provides a new fault detector based on calculating the rate of change of phasor voltage (ROCOV). It can be able to locate the faulty section using standard inverse-time characteristics and well distinguish between transient healthy and faulty conditions. The third strategy provides a new protection coordination scheme based on ROCOV. It does not require communications or adaptive protective devices to adapt the setting with any dynamic changes in generations or loads. Further, it is not affected by any topological changes.The proposed approaches are tested using different networks under wide variations in grid-connected and islanded modes of operation.The extensive test results indicate that the proposed schemes are highly selective and reliable in providing effective protection schemes

Issued also as CD