What's the Rush 2.0

The increasing penetration of Inverter Based Resources (IBRs) in the grid requires us to reconsider many previous firmly held assumptions that, if left unchallenged, could result in problems such as misoperation, equipment damage, and unnecessary re-work. One assumption often made in protective relay design involves the typical response of transformers to energization events. In a rotating machine dominated grid, transformers will experience between 8 and 12 times their rated current when energized. During this brief period there is a large percentage of second and fourth harmonics present in the current wave form. During this brief period there is a large percentage of second and fourth harmonics present in the current wave form. As power grids evolve to integrate increased penetration of IBRs, this behavior is no longer guaranteed. As a result, unexpected behavior during and after energization could cause misoperation of protective relays. This paper provides a follow-up to our previous paper, “What's the Rush? Can IBRs Handle Inrush Like Rotating Machines?” In that paper we studied the effects of inverter-based resources (IBRs) on transformer energization that could impact the performance of relaying. Using an EMT software, multiple vendor-specific inverter models were simulated as they were switched onto a transformer to model energization under various conditions of grid strength and IBR concentration. We found that, while no potential challenges to distance or overcurrent relays were detected, issues such as a persistent second and fifth harmonic content and inrush current could affect the performance of differential relays. Traditionally, second and fourth harmonics are used to discriminate between inrush and fault current. When IBRs are present in a sufficient quantity, they can generate a significant persistent second harmonic signal. This can impede recognizing that signature, which was traditionally known to be only generated during transformer inrush. Experimentation will be done to determine if traditional protective methods can still be effective. The primary focus of this follow-up paper is to recreate the behavior of a typical grid. Using an electromagnetic transients modeling program, inverter setpoints will be modified to bring inverter outputs close to values typically seen in a rotating machine-based grid. The resulting simulation outputs will be tested with differential and overcurrent relays using a relay test set. If the inverter output is not able to be modified to achieve this goal, further testing will be performed with modified relay settings that can accommodate the harmonic nature of IBRs. These experiments will focus on test relay operating in the presence of persistent second harmonics, fifth harmonics, and inrush currents that exist after modifying inverter setpoints. We will evaluate the effects of long-lasting inrush on the dependability of second harmonic inrush blocking, the security of fifth harmonic overexcitation blocking, and the operation of the differential element. Our goal in these evaluations is to find a balance between security, sensitivity, and dependability.