Experimental Analysis of Transmission Line Protection Functions in Grid-Connected IBR

This paper investigates protection challenges for line current differential (87L) and distance protection function (21) posed by the integration of inverter-based resources (IBR) into transmission systems. The reliability of these functions is investigated in a weak in-feed system, where the IBR is the only source of fault current. The analysis of the protection schemes is performed on a real-world 25 bus network system, using a time-domain transient program (EMTP). The test system is interconnected with an IBR source, converted into a white-box model in accordance with IEEE 2800-2022 matching the negative sequence injection, phase angle, voltage ride through, and reactive power control strategy. The IBR response to 15 fault cases is simulated and tested against EMTP protection function models, then recorded into COMTRADE files. These files are used in a power system simulator to test the response of manufacturer's 87 L and 21 protection functions inside three different types of physical microprocessor relays. The following was concluded: the simulation tripping time response matches closely to the hardware tripping time response, the relaying philosophy used in the presence of synchronous generators is not sufficient due to the unique IBR fault response, the effect on overcurrent supervisors of 21 and 87 L relays must be carefully considered, and ground protection functions are impacted based on the presence of a grounding transformer in the IBR.