PNNL

Abstract

The objective of this technical report is to outline the challenges of protection design for power systems rich in inverter-based resources (IBRs), synthesize current industrial practices, review new approaches from recent literature, and explore future opportunities in protection. IBRs are experiencing widespread adoption across both transmission and distribution systems. When present in significant quantities, IBRs challenge the performance of many traditional protection functions. To address these issues, the industry has developed sophisticated protection schemes that involve advanced relaying techniques in highly engineered pilot projects. However, these schemes are expensive and time-consuming to develop, build, and test. Researchers have proposed a number of new approaches for protection in IBR-rich distribution systems. Despite their potential, these new approaches do not address some major shortcomings of industry approaches stemming from complexity, practical requirements, and reliability. The essential findings of this report are as follows: • The protection methods currently being used to protect IBR-rich microgrids can also be applied to IBR-rich distribution systems and provide good performance if modern design methods are employed. Compared with traditional distribution protection schemes, microgrid protection generally makes greater use of transmission-oriented protection algorithms and communications. • Industry microgrid protection approaches are not economical for large-scale distribution systems. This is because they rely heavily on high-speed communications, complicated system-specific logic, detailed models of IBR behavior, and electromagnetic transients modeling (EMT). Thus, there is significant value to new protection techniques that reduce reliance on these factors. • Researchers have proposed a variety of new protection approaches for IBR-rich distribution systems. Some show promise for protection schemes that will scale more economically to distribution systems at large. Approaches based on unbalanced incremental quantities, such as incremental negative-sequence impedance, provide accurate fault detection and directional indications even in IBR-rich networks. Data mining approaches, such as random forest classification, provide a statistical framework for designing effective protection features while retaining transparency and determinism. • Approaches that are purely data-driven or those that rely on dynamically adaptive protection are unlikely to scale economically. In addition to requiring extensive studies to design, these approaches are difficult to integrate with established and trusted approaches for protection system testing. Based on these findings, Pacific Northwest National Laboratory has identified several avenues for further research. The use of modern data mining techniques for designing robust, reliable, and transparent power system protection algorithms should be explored. Modern directional elements are a promising line of inquiry for improving protection algorithm robustness against system operating conditions and IBR fault controls. There is a need for design strategies to confirm IBR protection elements are immune to uncertainties in IBR fault controls or variations in system operating conditions (e.g., microgrid vs. islanded operation). Design strategies are also needed for IBR protection based on short-circuit programs rather than EMT.