Protection of Inverter-Dominated Transmission Systems: First Experiences from Hawaii Island

The fast growth of inverter-based resources (IBRs) leads to inverter-dominated power systems, which has significant impact on power system protection. The hardware limitations of IBRs lead to significantly smaller currents during fault events compared to synchronous generators in traditional power systems. This characteristic also applies to grid-forming (GFM) IBRs which are required in inverter-dominated systems. Today, there is only limited knowledge and experience on protecting an IBR-dominated transmission system. This includes the required Fault-Ride Through (FRT) functions for GFM IBRs as well as how traditional protection functions respond to these FRT functions. In this paper, we summarize an extensive protection scheme analysis of inverter-dominated transmission systems. The analysis consists of a comparison of four commonly used generic FRT functions for GFM IBRs and three different protection functions (line distance, Permissive Over-reaching Transfer Trip (POTT), and line differential) in a variety of test environments. First, we study these functions extensively in a small power system model based on almost 1,000 electro-magnetic transient (EMT) simulations. Second, we implemented and compared these functions in a protection hardware-in-the-loop (PHIL) testbed consisting of a real-time simulation of the transmission system of Hawai’i Island interconnected with commercial protection relays. The comparison is based on 100 scenarios studied in the PHIL testbed. The main results show that distance protection, POTT, and differential show high protection dependability and security in IBR-dominated systems and good system stability after fault clearance as well as during non-fault events with appropriate FRT functions.