Impact of Inverter-based Resources on Impedance-based Protection Functions

Inverter-based resources (IBRs) may inject nonconventional or no negative-sequence current during unbalanced faults. The adverse impact of such fault current characteristic has been reported on fault type identification and directional functions that are essential to impedance-based protection. However, the impact of IBR negative current injection on the core part of different implementations of impedance-based protection function has not been thoroughly investigated. Latest German Gird Code introduces a new requirement for IBRs to inject negative sequence current proportional to its measured negative sequence voltage. In this paper, we will investigate if this requirement can address challenges and issues raised by IBRs for protection relays. This paper investigates and compares the impact of IBRs with two options 1- no negative sequence current injection and 2- negative sequence current injection based on latest German code on phase comparator based methods and impedance-based protection functions. Theoretical analysis, software simulation and commercial relay test have been used for this investigation.