System Specification for IEC 61850 is an optional component and is used to specify from a high level "what" the system should look like and "what" functions it should perform. It allows a standards based approach to design that provides a framework for creating repeatable and reusable engineering. It is not interested so much in the "how" a system is implemented- albeit the how will often be in mind during this phase to some extent. Given that the "what" is specified without the "how" it is the enabler of IEC 61850's desire for interoperability and interchangeability. The "Top down engineering" approach in System Engineering begins with the creation of a comprehensive System Specification. Thorough detail in the System Specification stage reduces engineering time and can simplify the later "System Integration" Stage.
The System Specification component of a design maps to the "substation" section of an SCD file. As a specification it is contained in the Substation Specification Description- SSD. The SSD file should contain a comprehensive specification of a substation automation system such as Single Line Diagram topology, voltages and bay layouts showing primary plant and functionality (logical nodes).
Fig. 1 HELINKS STS Single Line Diagram Report
HELINKS STS System Specification and Integration tools also has the ability to map virtual IEDs during the design Specification stages.
Fig. 2 HELINKS STS Functions mapped to Virtual IEDs
For meanings of acronyms and further details about IEC 61850 please read the "What is IEC 61850" article.