EirGrid and SONI Enforce Mandatory 1.0 Hz/s RoCoF Grid Code Standard Across All Island Substation Protection Relays
Irish transmission operators EirGrid and SONI have legally enacted the updated All-Island Grid Code requiring all generator step-up transformers, transmissio...
EirGrid and SONI Enforce Mandatory 1.0 Hz/s RoCoF Grid Code Standard Across All Island Substation Protection Relays
Irish transmission operators EirGrid and SONI have legally enacted the updated All-Island Grid Code requiring all generator step-up transformers, transmission substations, and BESS installations to withstand a Rate of Change of Frequency (RoCoF) of 1.0 Hz/s over a 500 ms rolling window, paving the way to an 85% System Non-Synchronous Penetration (SNSP) cap.
- Publish date: 2026-10-01
- Category: Standards & Policy
- Original source: EirGrid Group & SONI System Operations
- Reading time: 5 min
Pioneering Extreme Low-Inertia Island Grid Operations
Effective October 1, 2026, EirGrid (Ireland) and SONI (Northern Ireland) finalized the operational transition requiring 100% compliance with the 1.0 Hz/s RoCoF withstand standard. In small synchronous island systems dominated by offshore wind and solar, the sudden tripping of a major interconnector or power unit causes frequency to plunge far more rapidly than in mainland continental grids.
The mandatory standard prevents the cascade tripping of generator step-up transformers, loss-of-mains anti-islanding relays, and renewable feeder circuit breakers during high-RoCoF events.
Substation Protection Relay and Transformer Upgrades
Transmission asset owners invested over €140 million across 350 substations to reprogram digital numerical relays, recalibrate vector shift and frequency rate settings, and perform dynamic short-circuit mechanical stress simulations on aging power transformers.
With the standard fully enforced, EirGrid confirmed trial operations to lift the System Non-Synchronous Penetration (SNSP) limit from 75% to 85%, cementing Ireland’s global leadership in running an electricity grid on variable renewables.
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