Increasing the Rate of Change of Frequency limit to +/– 1 Hz/s

One of EirGrid’s and SONI’s key tasks as Transmission System Operators is to maintain balance between electricity supply and demand. EirGrid and SONI as TSOs faced a challenge in enabling the growth of renewable energy on the system so they worked to create a technologicially innovative solution. The goal was to increase the instantaneous non-synchronous renewable generation penetration limit. This is a key enabler for delivering a cleaner energy future.

Highlights

• Pioneers increased renewable energy penetration in the Ireland and Northern Ireland power systems via complex cross-industry involvement.
• Enabling this change made it possible to increase the instantaneous non-synchronous renewable generation penetration limit to 75%.
• Allowed EirGrid to trial the reduction in the minimum number of synchronous units required to be connected to the grid at any one time.
• Lowers the carbon intensity of the electricity supply in Ireland and Northern Ireland power systems by reducing the curtailment of renewables.

About the practice

Imbalances between supply and demand occur from time to time on the power system. For example, when a large electrical generator suddenly disconnects and its electrical power is lost, the supply from the system is temporarily below the demand and the system frequency begins to fall. An important metric when this happens is the Rate of Change of Frequency (RoCoF). This is a technical term describing the rate at which the frequency changes during a system imbalance event.

Events that result in high RoCoF levels can potentially lead to instability in the power system, so to help reach the target of 40% electricity generation from renewables, detailed studies identified a need to increase the maximum allowable RoCoF from 0.5 to 1 Hz/s on the Ireland and Northern Ireland power systems.

EirGrid and SONI established a multi-year and multi-stakeholder programme of work to change the RoCoF standard with multiple strands and numerous stakeholders including the Distribution System Operators, market participants and regulatory authorities in both jurisdictions. Key focus areas included: changing interface protection settings on the distribution system; conducting compliance testing of conventional generators; implementation by EirGrid and SONI of a state-of-the-art dynamic stability assessment tool with look-ahead capabilities to be able to monitor and assess RoCoF in real-time in the control rooms; and modification of the Grid Codes to reflect the new RoCoF standard.

In May 2023, following a successful operational trial and detailed studies, the RoCoF programme concluded and EirGrid and SONI are now operating the Ireland and Northern Ireland power systems with a RoCoF limit of 1 Hz/s. This operational capability will enable higher levels of renewable energy in Ireland and Northern Ireland.