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Impact of IBR Negative-Sequence Current Injection on Ground Fault Temporary Overvoltage and Ground Overcurrent Protection

Inverter-based resources (IBRs) are proliferating in distribution and transmission systems. These resources have been driving changes in industry paradigms, grid codes, standards, and recommended practices. One established utility system design is effective grounding for ground fault temporary overvoltages (GFTOV). This was derived entirely on the premise of a traditional grid, with utilities conforming their practices over the decades with the expectation of this topology to continue. As IBRs proliferate, traditional practices are becoming ineffective in depicting expected behavior. As a result, management of GFTOV becomes critically dependent on IBR control algorithms and on the negative sequence impedance of the aggregate load of a distribution feeder. This requires a shift in direction for transmission and distribution operators. This paper includes an electric utility's lessons learned in the interconnection of a range of large scale IBRs to its distribution grid. Two case studies are presented to illustrate the drawbacks of conventional practices. It also exemplifies how the utility manages the problem and presents a forward-looking perspective on the evolution of rules, standards, and practices.