The first Common Information Model (CIM)-based Long-Term Development Statements (LTDS) models were published by Distribution Network Operators (DNOs) in Great Britain in November 2025. Here’s TNEI’s take on them, what that means, and what’s coming next.
What is the Common Information Model (CIM)?
Common Information Model (CIM) is an internationally recognised semantic data model for power systems, defined under International Electrotechnical Commission (IEC) 61970 and 61968. It provides a consistent way to represent network components, topology and parameters, and improving interoperability between software tools and reducing reliance on bespoke formats. The Common Grid Model Exchange Specification (CGMES) is a set of CIM profiles developed by ENTSO-E that constrain CIM for specific grid-modelling use cases, enabling models to be exchanged and re-used consistently across parties and platforms. This is the standard applied in the GB context.
How is CIM being implemented for GB distribution networks?
Two things appear to be driving adoption in parallel:
- Regulation. Following Ofgem’s 2022 decision and subsequent LTDS reform direction, DNOs are now required to publish CIM (CGMES-compliant) network models in place of legacy Excel / text formats. The first EQ models were published on 28 November 2025.
- Software. In GB, IPSA (TNEI) and PowerFactory (DIgSILENT) are the two main packages with Attestations of Conformity to CGMES v3.0, issued by ENTSO-E in January 2024 and April 2025 respectively, and others will undoubtedly follow.
In parallel, National Energy System Operator (NESO) is pursuing wider CIM-based data exchange through industry code change, notably GC0139, covering both distribution and transmission representations for model exchange and whole-system planning.
Which CIM profiles are included in the first (Stage 1.3) release?
Only the Equipment (EQ) profile for the EHV network, which represents the existing licence-area grid down to the lower-voltage busbars of primary substations. The remaining profiles will follow in future releases through 2026 (see the milestones below).
The full profile set, once complete, is expected to cover:
- Physical: EQ, Short Circuit (SC) and Geographical Location (GL)
- Situation: Steady State Hypothesis (SSH), capturing operating conditions such as demand and generation
- Solution: Topology (TP) and State Variables (SV), representing processed topology and power flow results
- LTDS-specific: System Capacity (SYSCAP), providing bus-level fault levels, firm capacities and loadings
- Visualisation: Diagram Layout (DL)
A useful feature of this structure is that not every profile is needed for every study; the right subset can be applied to the question at hand.
How does CIM replace or coexist with legacy tabular LTDS data?
For now, CIM publications sit alongside existing LTDS tables. One DNO has indicated tabular publication may not continue indefinitely once CIM equivalents mature, but no transition date is set. Legacy tables remain the more complete source today because the current release covers only EQ; as the remaining profiles arrive through 2026, CIM will progressively become the authoritative exchange mechanism.
What did a review of the first published CIM models reveal?
TNEI reviewed the EQ models published by the 14 licensed DNOs across the five DNO groups, looking at asset volumes, element types, connectivity (islands) and impedance plausibility.
Our key observations from the EQ models are:
- Models range from around 3,000 busbars to over 25,000, now available in a consistent CIM format for the first time.
- Access arrangements vary, some DNOs allow immediate download after registration. Others require a shared data request form and several days’ approval.
- Visualisation is limited without the Diagram Layout (DL) profile, making connectivity hard to interpret.
- Data quality is mixed. Some impedance values fall outside expected ranges, and several models contain small islands suggesting missing elements or modelling choices.
- Naming conventions differ materially between DNOs (numeric IDs vs. site codes vs. full names), complicating automated cross-DNO processing.
- Running arrangements and Normally Open Points (NOPs) cannot be identified easily, limiting assessment of true connectivity and available capacity.
Given this is a first release, issues and limitations are to be expected, however it’s clear there are several areas where consistency and documentation need to strengthen.
Can CIM LTDS data be used for load flow, constraint analysis and connection design today?
Not quite yet, in most practical cases. The current release covers only EQ; operating assumptions (SSH), topology solutions (TP/SV), fault and capacity data (SC, SYSCAP) and solved cases all arrive in later stages. Combined with the data quality points above, CIM is probably not yet a drop-in replacement for legacy LTDS-table workflows.
The practical approach now is to prepare pipelines to consume CIM directly, validate against legacy LTDS where both are available, and expand use as the remaining profiles land through 2026. This is the approach TNEI is taking and adapting our curtailment and capacity assessment tools to consume CIM data directly in place of (legacy) tabular models.
What are the upcoming CIM milestones?
Deliverable | Date |
EQ model for the existing licence area | 28 November 2025 (Completed) |
EQ, SC and SYSCAP models for the existing grid and each of the next 5 years; capacity heatmaps | 29 May 2026 |
Solved cases; GL models for the existing grid and each of the next 5 years; grid development projects as Difference Models | 30 November 2026 |
Beyond the DNO roadmap, we’re keen to see equivalent CIM-based publication applied at transmission level, perhaps in future ETYS Appendix B releases!
Download a copy of our full paper on the CIM release or contact us to speak to our team of experts.
