As synchronous generators are progressively replaced by inverter-based resources, power system short-circuit levels decline and fault impact ranges expand. Gridforming (GFM) inverters can restore voltage-sourcecharacteristic fault current, yet their maximum overcurrent capability I max is hardware-limited and remains unspecied in current European grid codes. This paper develops a unied quasi-steady-state short-circuit model integrating synchronous generators, grid-following, and grid-forming inverters, and applies it to real European transmission grid data (PyPSA-Eur / OpenStreetMap) covering 11 regional subsystems. Through systematic I max scanning from 1.0 to 6.0 p.u. under three GFM penetration scenarios and both interconnected and systemsplit conditions, a recommendation extraction framework based on exponential saturation and capacityweighted compliance analysis yields region-specic recommendations of 2.53.5 p.u., forming a three-tier structure that reects grid topology, synchronous generation share, and interconnection level. A comparison of two representative current-limiting strategies conrms that both converge to identical system-level recommendations. These results provide quantitative input for national TSOs developing I max specications under ENTSO-E RfG 2.0.

Predicting sub-cycle transient peak currents from inverters within the first few milliseconds after fault inception is essential for instantaneous overcurrent protection coordination, yet the most commonly used standard for short-circuit calculation, like IEC~60909-0 and ANSI C037.010 addresses only quasi-steady-state currents. This paper proposes a closed-form analytical framework that decouples inverter fault current into hardware natural response and control-commanded response. The hardware natural response, governed by inverter output filter and passive grid resonances, dominates the first transient peak and requires only nameplate and filter data - no proprietary controller information. The control-commanded response, shaped by the current loop, phase-locked loop, and fault ride-through strategy, governs subsequent waveform evolution. Building on unified hardware modeling, the framework extends separately to Grid-Following and Grid-Forming inverters. Validation against electromagnetic transient simulations and power hardware-in-the-loop tests on three commercial inverters confirms prediction accuracy.

Predicting sub-cycle transient peak currents from inverters within the first few milliseconds after fault inception is essential for instantaneous overcurrent protection coordination, yet the most commonly used standard for short-circuit calculation, like IEC 60909-0 and ANSI C037.010 addresses only quasi-steady-state currents. This paper proposes a closedform analytical framework that decouples inverter fault current into hardware natural response and control-commanded response. The hardware natural response, governed by inverter output filter and passive grid resonances, dominates the first transient peak and requires only nameplate and filter data-no proprietary controller information. The controlcommanded response, shaped by the current loop, phaselocked loop, and fault ride-through strategy, governs subsequent waveform evolution. Building on unified hardware modeling, the framework extends separately to Grid-Following and Grid-Forming inverters. Validation against electromagnetic transient simulations and power hardwarein-the-loop tests on three commercial inverters confirms prediction accuracy.