by Keith Gray, POWER Engineers – a member of WSP, USA
IEC 61850-6-3, titled “Format of machine-processable rules for validation of IEC 61850 XML-based files”, was published in July 2025. IEC61850-6-3 introduces the use of Object Constraint Language (OCL), which is maintained by the Object Management Group (OMG), to validate System Configuration description Language (SCL) files. OCL is a significant advancement in the IEC 61850 engineering process because it enables rigorous, machine-processable validation of SCL files.
You may already be aware that SCL is described by an XML Schema Definition (XSD) which provides rules about the structure of the SCL XML. However, XSD cannot express many of the semantic and cross-referenced constraints required by IEC 61850 SCL. The limitations of XSD have been evident in UCA International Users Group (UCAIug) Interoperability (IOP) sessions, where SCL-related issues have consistently been a major source of interoperability problems. This gap is addressed by the introduction of OCL-based validation.
OCL provides a formal expression language that is used to define validation rules for SCL files. SCL files are then checked against these rules, and any rule violations are reported to the user. OCL expressions are defined against a UML-based information model, allowing constraints to be evaluated against structured representations of SCL data. In the current implementation, the UML model has been derived from the existing SCL XSD, as a native UML representation is not yet defined in IEC 61850-6. However, that will change with the next edition of Part 6, which will be renumbered to IEC 61850-6-1.
OCL rules can be defined by multiple sources. First, IEC TC57 WG10 will provide rules for each of the relevant parts of the standard (IEC 61850-6, IEC 61850-7-1, IEC 61850-7-2, etc.). The first release of these rules is in the final stages of preparation. Additionally, system integrators and end-users can create their own rules. The combination of the standard rules and the user-specific rules is expected to significantly improve the quality of SCL files across the industry. The figure below is a simple example of what an OCL rule looks like. The example rule verifies that unbufReport or bufReport must be true if maxReports is greater than 0. These attributes are defined in the services section of an IED within the SCL file. Similar rules can validate relationships between datasets, control blocks, logical nodes, and references across the SCL file, enabling a level of semantic validation that is not possible with the XML Schema alone. (See Figure 1).
A key milestone in the adoption of OCL-based validation will occur in the 2026 UCAIug IOP, where compliance with OCL rules will be required as part of the engineering process. The new process represents a shift from informal validation practices to a standardized, automated quality gate for SCL artifacts. OCL validation applies to ICD/IID files provided by the vendors, SSD/SCD files provided by the system engineering team, and hopefully to ASD files provided by the BAP and Functional Testing team. Validation against XSD and OCL will be automated and any violations will have problem reports created. A problem report will also be created if an issue is found with an OCL rule, ensuring that both the SCL files and the validation rules themselves are continuously improved.
OCL-based validation represents a fundamental improvement in how IEC 61850 systems are engineered. By enabling precise, machine-processable validation rules, it addresses longstanding challenges in SCL quality and interoperability. Its adoption is expected to play a central role in improving engineering efficiency and reducing integration issues across the industry, particularly as OCL validation becomes an integral part of engineering workflows and interoperability testing.
Biography:
Keith Gray (P.E.) received his M.S. in Electrical Engineering from Southern Illinois University Edwardsville in 2005. He is a protection, automation, and control engineer with over two decades of experience working for POWER Engineers, a member of WSP. He has focused on digital substations and IEC 61850 since 2014 and is the co-convener of IEC TC57 WG10. He is currently participating in multiple CIGRÉ working groups covering various IEC 61850 topics and he is active in the UCA International Users Group IEC 61850 interoperability events. He is a licensed Professional Engineer in the state of Idaho.
