CM097: Electromagnetic Transient (EMT) Root Mean Square (RMS) Model Submission for Transmission Owners (TOs)
What is being proposed
As Great Britain’s (GB) power system moves towards a net zero carbon operation; the number of Inverter-Based Resources (IBR) is expected to increase, with the amount of synchronous generation in the grid to decline which will significantly change the characteristics of the GB network These changes give rise to the need for more accurate dynamic modelling and the need for analysing the effect of potential control interactions between the devices across the network leading to risks of oscillations and inverter stability. This modification seeks to require Transmission Owners (TOs) to provide the ESO with Electromagnetic Transient (EMT) and Root Mean Square (RMS) models to carry out the required analysis.
Current status
(20/05/2024) New Proposal to be presented at May STC Panel, 03/06/2024 Workgroup Nominations going out 3 June 2024. 22/07/2024 Workgroups due to start in August/September 2024 following the completion of Urgent modifications. 03/09/2024 Awaiting completeion of urgent modifications before Workgroups can proceed.(06/10/2024) New Timeline to be presented at November STC Panel. 06/10/2024 New Timeline to be presented at December Panel as November Panel was cancelled. Workgroups due to start 16/12/2024, (05/12/2024) New timeline to be proposed at December's STC Panel on 11/12/2024, 06/01/2025 New timeline agreed, 1st workgroup is on 16 January 2025.07/05/2025: The Workgroup consultation opened on 28 March 2025 and closed on 22 April 2025. Workgroups to re-commence in May 2025. (05/06/2025) Workgroup Consultation completed, Workgroup meetings re-commenced on 5 June. 07/07/2025 Workgroup phase ongoing following Workgroup consultation. (03/09/2025) Workgroups are paused as agreed at August 2025 STC Panel until the related CUSC modification has been approved.
Details
Timeline
Analysis
NESO proposes requiring Transmission Owners to provide detailed Electromagnetic Transient (EMT) and Root Mean Square (RMS) models for grid stability analysis as inverter-based resources replace synchronous generation. The modification addresses control interaction risks and oscillation threats from the changing power system characteristics. Workgroups are paused pending approval of related CUSC modification GC0168.
Why it matters
This reflects the hidden costs of inverter-based generation transition — grid operators need expensive new modelling capabilities to maintain system stability as synchronous inertia disappears. The requirement socialises these analytical costs across transmission users while the modification process reveals regulatory complexity in managing cross-code dependencies.
Key facts
- •Workgroups paused until related CUSC modification GC0168 approved
- •High impact on Transmission System Operators and Owners (onshore & offshore)
- •First workgroup rescheduled multiple times, now dependent on cross-code approval
- •Addresses inverter stability and oscillation risks from declining synchronous generation