CIM
The Common Information Model, and why every GB DNO speaks it.
CIM is the IEC 61968/61970 data model for power systems. It describes what an asset is, how assets connect, and how they behave. GB LTDS, SCADA vendors, vendor planning tools, and the emerging MHHS data flows all use derivations of CIM. This route explains the model, the hierarchy, and the GB profiles.
21Route 21 · Data and standardsAfter this route you will be able to
- Explain what CIM is and which parts of IEC 61968/61970 relate to which functions.
- Trace the class hierarchy from IdentifiedObject down to specific equipment classes.
- Describe what a CIM profile is and why LTDS uses four of them.
- Identify the common serialisations: RDF/XML, RDF/Turtle, XML with embedded RDF.
- Use the LTDS validator to exercise your understanding against real data.
1999IEC 61970 first published · CIM starts life as an EPRI standard
A North-American utility research project became the data model every large grid now uses.
CIM began in the 1990s as a project of the
Adoption took a long time. Vendors had their own data formats and little incentive to converge. What changed the equation was cost of integration: every utility building a new system faced the choice between reinventing a model or aligning with CIM. Slowly, then quickly, the CIM-shaped world became cheaper to build than the bespoke one.
Today every major GB DNO control system, every vendor planning tool (DigSilent, PowerFactory, PSS/E, ETAP, Siemens), and every market data flow in MHHS builds on CIM derivatives. LTDS is the most visible GB expression. The less visible uses are everywhere.
CIM is three decades old. Why does the model still work, and what does its structure actually tell a GB analyst?
The answer is the class hierarchy. Once you understand it, every CIM file becomes readable.
Section 01 · Class hierarchy
IdentifiedObject at the top. Specialised equipment at the leaves.
CIM is an inheritance hierarchy. A Transformer is a kind of ConductingEquipment is a kind of Equipment is a kind of IdentifiedObject. Understanding the top three levels is enough to read most files.
IdentifiedObject
The root class. Everything in CIM inherits from it. Attributes: mRID (master resource ID), name, description, aliasName.
PowerSystemResource
A physical or logical part of a power system. Abstract; concrete subclasses below.
Equipment
A physical asset (transformer, breaker, generator, line). Has terminals and ratings.
EquipmentContainer
Holds other equipment. Substation, Line, VoltageLevel, Bay are all EquipmentContainers.
ConductingEquipment
A specialisation of Equipment that conducts current. Transformers, breakers, lines and generators are all ConductingEquipment.
PowerTransformer
Two- or three-winding transformer. Has TransformerEnds, each connected to a Terminal.
Breaker
A switch that opens and closes to interrupt or restore current flow. Subtypes exist for vacuum, SF6, oil-filled, etc.
ACLineSegment
A section of overhead line or cable. Has resistance, reactance, admittance, rated current, length.
SynchronousMachine / EnergyConsumer
Generator classes and load classes. Each has specific operating parameters.
Every LTDS file is a graph of IdentifiedObjects, connected through their inheritance tree and their association relationships. The four LTDS profiles each restrict attention to a subset of this hierarchy.
Section 02 · What is a profile?
A subset of CIM, with extra constraints, for a specific purpose.
Raw CIM has thousands of classes. No single exchange needs all of them. A profile picks the classes needed and tightens the rules (mandatory attributes, allowed cardinality, allowed values).
Equipment profile (EQ). The physical and topological model: substations, transformers, lines, switchgear, protection relays. For LTDS v2-1-0, this is EQ v7.
Short Circuit Result profile (SCR). Pre-computed fault-level data at each node. Computed from the Equipment model under specific fault scenarios. LTDS uses SCR v3.
System Capacity profile (SYSCAP). Capacity, demand forecasts, headroom data. This is the profile that connection applicants and developers most commonly read. LTDS uses SYSCAP v5.
Header profile. Submission metadata: who published, when, version, change log. Not power-system data per se; the governance wrapper around the data.
Profiles are defined by SHACL shapes. A shape lists the required properties for each class, the allowed datatypes, the allowed cardinality, and cross-references between classes. A submission is valid if every shape's rules hold.
A CIM profile is a subset of the CIM data model that is tailored to a specific information exchange. A profile specifies which classes and attributes are used, their cardinality, and their semantic constraints. Profiles enable interoperable exchange between parties using the same CIM base.
IEC 61970-301 (Base CIM) and IEC 61970-552 (CIM profile definitions)
Section 03 · Working with CIM data
Parse it yourself or use a library?
A CIM file is RDF. Two mainstream approaches to reading it.
Check your understanding
Three questions on what you have just read.
Key takeaways
- CIM is IEC 61968/61970. Three decades old, widely adopted, stable.
- Class hierarchy top: IdentifiedObject → PowerSystemResource → Equipment → specific classes.
- A profile is a subset of CIM plus extra constraints, defined by SHACL shapes.
- LTDS v2-1-0 uses four profiles: EQ, SCR, SYSCAP, Header.
- Three main ways to work with CIM data: general RDF library, vendor tool, triple store with SPARQL.
References
- IEC 61970 (transmission CIM)
Base CIM for transmission and planning.
Primary standard.
- IEC 61968 (distribution CIM)
Distribution CIM extension.
Distribution standard.
- W3C SHACL
Shape-based validation language.
Profile constraint mechanism.
- Ofgem: LTDS
GB LTDS v2-1-0 profile usage.
GB-specific regulatory source.
That completes the architecture and LTDS routes. The history routes in Wave 3 give the long view of how GB energy got here.