Mitigating Directional Protection Challenges in Transmission Systems with Inverter-Based Resources: Modeling Negative Sequence Current Injection in Compliance with IEEE Std 2800-2022

IEEE Std 2800-2022 was developed to establish minimum technical requirements for the interconnection of IBRs with transmission and sub-transmission systems. Among its many provisions, the standard includes specific requirements related to fault response capabilities, including the injection of negative-sequence current during unbalanced faults. This capability is critical for the proper functioning of many conventional protection schemes, especially line protection which utilizes directional relays that rely on negative-sequence or zero-sequence quantities to declare a forward or reverse fault.

This paper examines the limitations of traditional line protection schemes in systems with high

IBR penetration. These limitations become particularly pronounced under weak grid conditions or in cases where the system lacks adequate directional polarization sources. In such environments, conventional protection schemes may misoperate or entirely fail to trip, thereby compromising system reliability and safety. Through detailed analysis, we demonstrate how IEEE Std 2800-2022 aims to mitigate these risks by requiring fault current characteristics that enhance fault identification and polarization under evolving grid conditions.

A key difference between conventional synchronous sources and IBRs lies in their fault current contributions. While synchronous machines naturally provide fault currents composed of positive-, negative-, and zero-sequence components depending on fault type and network topology, IBRs often do not contribute negative- or zero-sequence currents unless specifically designed to do so. Lack of negative-sequence current prevents directional element polarization, leading to potential misoperations during unbalanced faults.

A case study involving a realistic transmission system modeled under three distinct operating conditions is presented:

1. Base case featuring only synchronous generation and no IBRs.

2. A scenario with synchronous sources replaced with an IBR that does not inject negativesequence current.

3. A final scenario in which the IBR is fully compliant with IEEE Std 2800-2022 and is capable of injecting negative-sequence current during unbalanced faults.

The protection system's performance is evaluated using steady-state RMS phasor-domain simulations. Results show that the ability of IBRs to inject negative-sequence current is a key enabler for reliable directional protection. Without it, polarization may be insufficient, leading to incorrect fault direction determination or delayed tripping. These findings underscore the importance of ensuring IBRs meet fault performance standards to support protection system dependability and security in high-renewable grids.

Traditional line protection schemes are evaluated under all scenarios. While these schemes were historically implemented using electromechanical or solid-state technology, modern digital relays are now commonly used. Although microprocessor-based relays are more advanced, they utilize algorithms similar to electromechanical models. Therefore, microprocessor relays are used in the simulations. Specialized protection schemes—such as current differential, blocking or permissive, and phase comparison are not included in this analysis.