Changing generation is resulting in lower system inertia and increasing costs, with residual inertia making up a larger percentage of the total system inertia. The ability to measure real-time inertia will enable both synchronous and residual inertia to be known, improving decision making and reducing the risk of the system running insecure. There is currently no best practice or standardisation for measuring system inertia. This project will analyse and verify data from new commercial inertia monitoring tools and compare to NGESO operational data, establishing different generation and demand scenarios for inertia and Rate of Change of Frequency (RoCoF). Through development of measurement parameters and specifications for reference instrumentation, the project will build on existing data and use cases with the goal to establish standardisation for inertia measurement.
Benefits
The ability to measure real-time inertia will enable both the synchronous and residual inertia to be known, resulting in improved knowledge and better informed decision making. More accurate inertia values, especially against different generation and demand use cases, will reduce the risk of the system running insecure.
Managing RoCoF as a result of low inertia is costing approximately £200m per year, a more accurate measurement could result in a reduction in these costs and provide added transparency to decision making.
Improved measurement and forecasting capability will be able to feed into pathfinder assessments, helping to define the required volume, where it should be purchased and potentially enable the future despatch of inertia services.
Learnings
Outcomes
1. Assessment of the plausibility of results from commercial inertia measurement systems with respect to existing inertia estimation. Identification of scenarios in which measured and estimated inertia have smaller/larger divergences.
2. Assessment of the extent and effect of regional differences in frequency, its rate of change and inertia in the GB power system. Along with frequency measurement results, the results may be used to plan regional inertia monitoring requirements and optimize local frequency management.
3. Use cases and measurement requirements for frequency, its rate of change and inertia have been documented. This information may be used to review existing and specify new requirements for response times of frequency services.
4. Methodology for validation of inertia measurements has been developed. This includes a method for reference measurements of the RoCoF due to inertial response to loss of large infeed events. The methodology provides a framework to assess the extent to which inertia measurement results from commercial systems meet the requirements of the main use case of predicting the frequency trajectory after large disturbances. The methodology has been presented to international Working Group CIGRE C2.45 which is preparing a technical brochure providing guidance on ‘Estimation, evaluation and provision of power system inertia in networks with a high share of renewable generation’ due to be published in 2026, and to IEC TC8 for considerations on a future standard on power system inertia.
5. The absolute accuracy of the commercial systems measurement results and of NESO’s inertia estimation has been quantified using reference RoCoF measurements from NPL’s instruments installed in different network locations. The results enable NESO to assess and optimise the reliability of inertia measurements and estimations for operational use.
Lessons Learnt
Future projects should anticipate that setting up data access and installation of non-standard software packages can take several months. Contingency should be allowed for delays in installation of instruments in high-voltage substations. The verification procedure requires information about the size of the power loss which is published in NESO’s system incident report GC105 which has a lag time of 3 to 4 months, this should be considered in the timeline of future projects using information from this report.
