PROTECTION OF MODERN DISTRIBUTION SYSTEMS

Abstract

Motivated by the potential for improvements in the electric distribution system’s protection schemes, this dissertation examined the challenges facing protection schemes due to the integration of Distributed Generators (DGs). Traditional protection schemes for radial distribution systems were designed based on the unidirectional power flow from the source down to the loads. Protective devices typically use are overcurrent relays, autoreclosers, fuses, and circuit breakers. However, these protective schemes may no longer be sufficient to ensure correct operation in the new era of distribution systems integrated by DGs. This dissertation investigated the impact of DGs that might mislead the protection schemes in distribution systems. Understanding these impacts are helpful for improving protection schemes solution methodologies. This dissertation also presented multiple solutions for protection schemes aimed at mitigating the negative impacts of integrating DGs into radial distribution systems. The first proposed solution provided improvements for distance relays (DRs) that were proposed recently to protect radial distribution feeders (RDFs). This solution consisted of three new methods to accurately calculate the measured positive-sequence impedance by DR in the presence of the infeed effect. These methods depended only on local measurements making them cost-effective and easy to implement compared to other solutions that depend on communication links. The second solution proposed a new approach to control inverter-based DGs (IBDGs). This approach limited the fault current in distribution systems by controlling single-phase inverters that connect distributed generators to distribution systems. Finally, this dissertation proposed an accurate and reliable model for the resistive superconducting fault current limiter (SFCL). The performances of the proposed methods were demonstrated with radial distribution system models in PSCAD™/EMTDC™.