# 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:** policy-standards
- **Reading Time:** 5 min
- **Original Source Citation:** [EirGrid Group & SONI System Operations](https://www.eirgridgroup.com/newsroom/press-releases/2026/all-island-grid-code-update-1hz-rocof-compliance-substations-october-2026)
- **Tags:** EirGrid, SONI, All-Island Grid Code, RoCoF, SNSP 85%, Ireland Grid, Frequency Stability, Transformer Protection
- **Canonical URL:** https://voltformer.com/news/eirgrid-soni-enforce-1hz-per-second-rocof-grid-code-substation-standard
- **Markdown Source:** https://voltformer.com/news/eirgrid-soni-enforce-1hz-per-second-rocof-grid-code-substation-standard.md

## 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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