The TRW (Transmission Reinforcement Work) study shows that over the next ten years, a significant area of the transmission network will exceed the existing 63kA maximum fault current capability if the PPM (Power Parked Module)-based wind and solar generation and batteries feeds a minimum fault infeed of 1pu into a fault. Many sites might have to be rebuilt with 80kA fault level capability or run split. The project aims to develop an innovative method which control cumulative fault infeed in order to manage maximum fault levels in the future network and reduce the need for reinforcement.
Benefits
It is anticipated that the project will create an innovative solution that will eliminate or reduce the need to upgrade existing sites to the higher fault level capability of 80kA, or run sites split. The upgrade/rebuild of sites would cause significant delay to new renewable connections and would be excessively costly. Running sites split can result in increased network thermal and stability constraint costs due to the reduced network capability to balance power flow and the increased impedance of the network. Therefore, the project facilitates the energy transition in that it will accelerate renewable generation and battery connections and bring cost benefit to consumers.
Learnings
Outcomes
2024/2025
A comprehensive survey of global code requirements, industry experience, and best practices has been completed. A report has been produced that reviews international code requirements and industry practices related to Power Park Module (or IBR) fault level management and its impacts. Innovative methods have been proposed to manage cumulative fault infeed. Based on discussions with key stakeholders, it is suggested that making fault infeed a function of pre-fault active power output be considered for further development and validation.
2025/2026
RMS and EMT fault studies for WP3 and WP4 were undertaken, along with recommendations and further actions based on the findings – the results of these will be published in the relevant technical documentation on the ENA portal. A summary is given below:
Recommendations for further work
The key recommendations from this project are:
1. Coordinated action
1.1. Fault Level Working Group
Formalise the Fault Level Working Group and broaden the industry representation.
2. Improved Modelling
2.1. How fault infeed is calculated
Develop a large-scale project to improve transmission system fault level modelling
Update the core method for calculating fault infeed (G74)
Use time-domain simulation for voltage recovery – EMT and RMS;
Perform validation – real events, test short-circuits, EMT;
Update requirements for User Data, once the modelling approach is identified.
2.2. How the worst-case scenario for fault levels is defined
Continue development of assumptions for connections (already in hand) and retirements;
Apply probabilistic operating scenarios for the over-built system;
Coordinate the planning approach with operational measures – active management of fault level (FL) constraints by NESO, similar to thermal, voltage and stability constraints.
3. Revised IBR FFCI specification
3.1. Grid Code Modifications Engagement
Monitor and engage with Grid Code Modifications to ensure that FL considerations are appropriately accounted for.
Use the Grid Forming Grid Code (GC) Mod to implement “quick wins” on the IBR Fast Fault Current Injection (FFCI) specification.
3.2. Optimising FFCI from IBRs
Carry on research into optimising FFCI using improved fault infeed calculation methods and probabilistic sampling and cut-off. Implement changes via GC Mod.
Further details can be found in the WP4 report.
TRL
TRL at start: 3
TRL at end: 5
Total NIA Expenditure on project
Total Spend: £553k
Internal and Indirect Spend: £112k
External Spend: £441k
Net Benefits
The TRW study indicated that significant reinforcement would be required to manage 42 sites exceeding the current maximum 63kA fault level by 2033. The baseline solution would be upgrading those sites with 80kA fault level capability or running the sites split. It is assumed that 50% of the issues can be resolved via upgrading the sites with 80kA fault level capability and the rest of can be resolved via running the sites split. Both solutions come with a significant cost. Running sites split will increase the operability risk, reduce the network capability to balance the power flow and lead to increased thermal and stability constraint costs. The rebuild solution requires significant reinforcement, outages and introduces uncertainty and delay to customer connections. It is believed that an innovative solution can effectively reduce the cumulative fault level in the future network and thus significantly reduce the number of the sites requiring to be upgraded with higher fault level capability or running split. The key benefits calculated are based on savings in reduced reinforcement and constraint costs by 2035/36. The estimated NPV cost benefit of this project is significant and could reach around £73m per feasible site if the project is successful and the innovation method can be rolled out across GB.
All benefits are dependent on grid code changes and further innovation projects to understand if the proposed methods are feasible across the relevant 63kA sites. This includes engagement with other transmission owners and the energy system operator to collectively devise an industry-wide fault level management strategy.
Lessons Learnt
2024/2025
No lessons learnt for future projects to report at this stage.
2025/2026
Key lessons learnt are:
· The need for industry alignment on terminology on system strength and fault levels, as current definitions can often be ambiguous.
· Fault level calculations are based on a method that is not fit for the modern power electronic grids.
· Cross-industry engagement and a unified strategy between transmission owners and the system operator is necessary
