With the increasing demand for electricity and the expansion of electrification, advancements
in substation automation systems have become essential. A secure and reliable protection scheme is a cornerstone of these systems, ensuring robustness and redundancy across all components. Digital substations utilizes Process Bus Sampled Values (SV) and Generic Object-Oriented Substation Events (GOOSE) to improve the system response time, interoperability among technologies, decreasing the substation footprints.
This dissertation investigates the performance and response of protection systems in digital substations, focusing on transformer differential protection. Key challenges, such as interoperability among vendor-specific implementations, communication network conditions, and the quality of measurements, are explored. These issues are addressed through research questions centered on interoperability, data integrity, and modern communication technologies.
A significant contribution of this work is the development of multiple hardware-inthe-loop (HIL) testbeds to evaluate protection schemes. A cost-effective platform utilizing a Raspberry Pi with a real-time Linux operating system was established, providing flexibility for testing protection algorithms. The research reveals that merging units (MUs) from different vendors exhibit varying transient responses, which can compromise transformer differential protection during conditions such as inrush or overexcitation. While IEC 61850 promotes interoperability, vendorspecific frequency response differences must be compensated to prevent spurious relay operations.
The study also examines the effects of consecutive SV losses on protection IEDs. Varying tolerances to SV packet losses among IEDs were found to affect dependability and security, potentially undermining protection performance. To address these challenges, two innovative solutions were introduced: Data Repairing for Protection IEDs (DRPIED) and the Backup Subscription Scheme (BSS). DRPIED uses High-Order Dynamic Mode Decomposition (HODMD) to reconstruct lost SV data with minimal error, achieving real-time processing. Meanwhile, BSS provides redundancy by rerouting SV streams when primary streams fail. Both solutions were validated through HIL testing, demonstrating significant improvements in SV loss tolerance and security and dependability of the protection IEDs.
Additionally, the integration of 5G communication into digital substations was explored using a real-time cyber-physical testbed and local 5G communication network for distance pilot protection scheme. By combining power system simulations with network emulation, the platform evaluated the impact of latency, jitter, and reliability on protection schemes. Results showed that 5G-assisted protection schemes deliver fast fault detection and response times, highlighting the transformative potential of advanced communication networks in substation automation.
Overall, this dissertation provides insights into the challenges and solutions related to the performance and reliability of protection systems in digital substations, shedding light on the potential of emerging technologies like 5G in this domain. This aligns with the increasing demand for advanced, reliable, and secure substation automation systems in the context of growing electrification
