How to Know if an SCL File is Valid and Compliant with the IEC 61850 Standard?

The IEC 61850 Standard: Why Validating SCL Files is Essential for Substation Automation

The IEC 61850 standard is widely adopted for electrical system automation. It defines data models, communication services, and a configuration language for integrating Intelligent Electronic Devices (IEDs) within substations. At the heart of this standard lies the System Configuration Language (SCL), which plays a crucial role in describing system topology, device communication, and equipment configuration.

In theory, any configuration software should be able to read an SCL file without issues, ensuring interoperability across different vendors. But in practice, things are not so straightforward. Many vendors introduce custom modifications to these files to suit their internal systems—often compromising cross-platform compatibility. Engineers then find themselves spending valuable time identifying inconsistencies, exchanging countless emails with vendor support teams, and deciphering proprietary adaptations. What should be an automated process turns into a lengthy cycle of reviews and fixes, stretching projects that could be completed in weeks into several months of work.

The challenge is amplified by the fact that SCL files, though human-readable, are highly complex. Manually validating thousands of lines of configuration—especially when dealing with slight variations between standard versions or differing vendor interpretations—is nearly impossible. This is particularly true for large-scale projects involving equipment from multiple manufacturers and massive volumes of configuration data (see Figure 1).

To ensure true interoperability and avoid misconfigurations in substation systems, validating SCL files against the IEC 61850 standard is critical. In this article, we’ll explore how SCL files are defined within the standard, the most common issues that arise, and why using independent validation tools is essential to detect errors and ensure full compliance with IEC 61850.

SCL Language According to IEC 61850

In substation automation projects, the engineering phase often starts before the equipment is physically installed. IEDs can perform multiple functions within the system, but their flexibility doesn’t mean all of these functions can operate simultaneously. Therefore, it’s essential to define specific profiles for each IED, selecting only the capabilities required for the particular application.

Although the devices support self-description features, it is critical to have standardized files that define their configurations and functionalities from the early stages of the project. This facilitates proper planning and helps minimize risks such as incompatibilities or operational limitations during commissioning.

To ensure interoperability between tools from different manufacturers, the IEC 61850-6 standard defines the System Configuration Language (SCL), which serves three key purposes:

• Functional system definition: Enables the formal description of the relationships between the automation system and the process (e.g., substation, switchyard).

• IED characterization: Describes the configuration of the automation IEDs and their communication systems.

• Technical documentation: Centralizes the system configuration, simplifying its maintenance and updates throughout its lifecycle.

SCL is a high-level language defined as an XML schema, which can be used to create plain text file formats that describe application-specific structured data. The key advantage of this approach lies in its dual capability: while computers can process it automatically, engineers can also read and understand it when needed.

Because it is based on XML, it inherits several key characteristics: it is hardware- and software-independent, fully extensible, and adaptable to various needs without compromising its fundamental structure. However, this flexibility operates within strict boundaries defined by the official IEC 61850 standard schema.

The IEC distributes this schema as a set of XSD (XML Schema Definition) files that define the structure and content of SCL files, effectively acting as "building rules" for SCL file creation. As shown in Table 1, each XSD has a specific role in the validation process:

Tabla 1. Archivos que componen la definición del esquema XML para SCL. 

File Name	Description
SCL_Enums.xsd	The enumerations used in the XML schema.
SCL_BaseSimpleTypes.xsd	Basic simple types used by other parts.
SCL_BaseTypes.xsd	Definitions of basic complex types used by other parts.
SCL_Substation.xsd	Syntax definitions related to processes (Process, Line, Substation).
SCL_Communication.xsd	Syntax definitions related to communication.
SCL_IED.xsd	Syntax definitions related to IEDs.
SCL_DataTypeTemplates.xsd	Syntax definitions related to data type templates.
SCL.xsd	Main syntax definition of the SCL schema; defines the root element of every SCL file.

These XSD files go beyond the basic rules of XML, adding layers of validation specific to the electrical domain:

• They define the mandatory hierarchy of elements.

• They establish required/optional attributes.

• They specify the allowed data types.

• They control the relationships between components.

When an SCL file complies with its corresponding XSD, it ensures that any IEC 61850-compliant system can interpret it correctly, maintaining the interoperability that makes the standard so valuable. Therefore, ensuring that vendor equipment strictly adheres to this schema is the first step in developing IEC 61850 digital engineering projects.

In this case, it’s worth making a few remarks: 

1. There are at least six different purposes for SCL data exchange, and therefore six types of SCL files that must be distinguished when exchanging data between tools. This is done through different file extensions (ICD, IID, SSD, SCD, CID, SED).

2. Currently, there are four versions of the SCL schema available for validation: the Edition 1, 2, 2.1, and 2.2 schemas of the IEC 61850-6 standard.

3. For Edition 2 of the IEC 61850 standard, there are three revision numbers: A, B, and C. However, only one is currently valid, Revision C. Still, some versions of configuration tools may use Revision A or B due to the fact that some manufacturers did not update their tools in a timely manner.

Tabla 2. Versiones publicadas de la norma IEC 61850-6. 

Edition	Publication Date	Webstore	Namespace
Edition 1.0	2004-03	IEC 61850-6:2004	IEC 61850-6:2003
Edition 2.0	2009-12	IEC 61850-6:2009	IEC 61850-6:2007B
Revision 1 de Edition 2.0	2018-12	IEC 61850-6:2009/AMD1:2018	IEC 61850-6:2007B4
Edition 2.1	2018	IEC 61850-6:2009 + AMD1:2018 CSV	IEC 61850-6:2007B4
Revision 2 de Edition 2.0	2024	IEC 61850-6:2009/AMD2:2023	IEC 61850-6:2007C5
Edition 2.2	2024	IEC 61850-6:2009 + AMD2:2023 CSV	IEC 61850-6:2007C5

Recurring Issues in SCL Files and Their Impact on IEC 61850 Projects

So far, we’ve defined what the SCL language is and how its general schema, defined in the XSD files, allows for structural validation. Below, we outline the specific issues that may arise in SCL files during the configuration of IEDs, particularly in multivendor integrations:

• Arbitrary placement of new equipment in the SCL hierarchy:
  The standard defines a clear structure (Substation → VoltageLevel → Bay → Equipment), but some manufacturers place their IEDs in parallel, non-standard structures. When imported into other software tools, this can lead to errors and make the files unusable.

• Naming rule violations:
  The standard specifies strict conventions for naming IEDs, Datasets, and messages, including rules on length and the use of special characters. However, some vendor tools fail to alert users to these violations, allowing the use of underscores or spaces. These naming errors often lead to unresolved references during integration with other software tools.

• XSD alteration:
  Some manufacturers modify the XSD schemas to relax restrictions by adding proprietary elements. While this may allow certain files to appear valid within their own tools, it often causes those same files to fail when used in other systems.

• Undocumented extension of data types:
  Some manufacturers modify or extend the dataTypes defined in the IEC 61850 standard without following proper procedures. As a result, these custom data types are not recognized by equipment from other vendors, hindering interoperability.

• Use of custom namespaces:
  Some manufacturers, in their private sections, reference proprietary namespaces without providing an associated XSD schema for access and validation. This prevents proper verification and can lead to compatibility issues.

• Loss of information during SCL conversions:
  Some tools fail to preserve essential data when converting between different SCL file types (ICD, IID, SSD, SCD, CID, SED). Key elements such as descriptions (desc), units (unit), device names (IEDName), or multicast subscriber declarations are sometimes lost in the process, preventing proper implementation in other software tools.

Considering all of the above, we can conclude that the first step in any IEC 61850 digital project is to validate the SCL files that will be part of the system, especially in projects involving IEDs from different manufacturers. This validation is crucial to reveal any potential non-conformities with the IEC 61850 standard that could cause interoperability issues.

Methods for Validating an SCL File

1. Manual Validation

This method involves manually reviewing the structure of the SCL file in XML format, which requires extensive knowledge of the IEC 61850 standard and its data schemas. However, due to the complexity and the number of technical details involved, this approach carries a high risk of error, potentially leading to incorrect configurations or incompatibilities between devices.

2. Use of Automated Validators

To minimize errors and optimize the process, the use of automated validation tools is highly recommended. These tools analyze the conformity of the SCL file with the IEC 61850 standard by validating it against the XSD schemas corresponding to the specific version of the standard being used. Furthermore, the validation tool should be independent of vendor-specific software, which may be biased due to proprietary configurations.

The main benefits of these validators include:

• They eliminate the need for manual review, reducing the risk of incorrect configurations.

• They verify that files comply with the specific requirements of the standard.

• They allow validation of multiple files in a short time, accelerating the configuration process.

Introduction to the SCL Validator in ATLAN

To ensure the correct implementation of IEC 61850 projects, the ATLAN software includes an automated SCL file validator, designed to detect potential incompatibilities before integrating multi-vendor equipment. This tool ensures strict verification of files against the standard, identifying interoperability risks.

Its main features include:

• Verification of structural and syntax errors, data types, and naming rules according to the XSD schema.

• Compatibility with the different types of SCL files (ICD, IID, SSD, SCD, CID, SED).

• Compatibility with different versions of the IEC 61850 standard, including Ed1, Ed2, and Ed2.1.

• Generation of incompatibility reports for auditing purposes.