IEEE 1547-2018 Fault Ride-Through Requirements and Protection Implications

Fault Ride-Through (FRT) originated from wind turbine grid codes in Europe (e.g., German BDEW) and was formalized in IEEE 1547-2018 to address the systemic risk posed by mass inverter disconnection during transmission faults. Unlike synchronous machines—which inherently deliver high, decaying fault current due to rotor flux dynamics—inverter-based resources produce near-zero subtransient current unless explicitly commanded, and their current is limited by semiconductor ratings and control bandwidth.

This fundamental shift demands rethinking protection design: traditional overcurrent relays (50/51) rely on magnitude and time, but inverter fault current may never exceed 1.5× rated current—even during a bolted fault—rendering them insensitive. Instead, modern schemes use voltage-based triggers (e.g., 27/59), negative-sequence detection (46), or traveling-wave fault location (TWF) to identify faults faster than the inverter’s control loop can react. Coordination now centers on aligning relay operating time with the inverter’s FRT envelope—not vice versa.

At the system level, FRT introduces new stability concerns: excessive reactive current injection during deep sags can cause local overvoltage if downstream capacitors or lightly loaded feeders resonate, while delayed fault clearing may violate NERC TOP-002-3 (transient stability). Advanced implementations embed grid-forming (GFM) mode activation *after* FRT completion to restore inertia emulation—blurring the line between protection and control. This convergence means protection engineers must now collaborate with controls engineers on firmware-level logic, not just relay settings.