The following is an outline of the IEC61850 document. The various parts are often referenced during discussions of the different areas.
1. System aspects
• Part 1 – Introduction and overview
• Part 2 – Glossary
• Part 3 – General requirements
• Part 4 – Systems and project management
• Part 5 – Communication requirements for functions and device models
2. Configuration
• Part 6 – Configuration language for electrical substation IEDs
3. Abstract communication services
Implementing IEC61850 in Equipment and Systems
4. Data models (Basic communication structure for substations and feeder equipment)
• Part 7-3 – Common data classes
• Part 7-4 – Compatible logical node classes and data classes
5. Mapping to real communication networks
• Part 8-1 – Mapping to MMS and to ISO/IEC 8802.3
• Part 9-1 – Serial unidirectional multi-drop point-to-point link
• Part 9-2 – Mapping on an IEEE 802.3-based process bus
6. Testing
• Part 10 – Conformance testing
6.2.2 Object Modeling
Object models are nouns with predefined names and data structures. Objects are the data that are exchanged among different devices and systems. There are typically hundreds to thousands of different objects, each with a unique name within its domain so that it can be uniquely identified. Figure 6-3 illustrates object modeling (OM), showing the object hierarchy used for developing OM-SA object models. As can be seen from this diagram, one horizontal component is labeled OM for object model and one vertical component is labeled SA for substation automation. The cross between these two components represents the substation automation object models defined in IEC61850-7-3 and 7-4.
Key Technical Point
Object models are nouns with predefined names and data structures. They are the models of the data that will be exchanged. OM-SA defines the object models for substation automation.
Implementing IEC61850 in Equipment and Systems
Figure 6-3
Object Model Hierarchy
6.2.2.1 Object Model Structure
The OM structure from the bottom up (as shown in Figure 6-3) is described here:
• Standard data types: Common digital formats such as Boolean, integer, and floating point.
• Common attributes: Predefined common attributes that can be reused by many different
objects, such as the quality attribute. These common attributes are defined in IEC61850-7-3 clause 6.
• Common data classes (CDCs): Predefined groupings building on the standard data types
and predefined common attributes, such as the single point status (SPS), the measured value (MV), and the controllable double point (DPC). In essence, these CDCs are used to define the type or format of data objects. These CDCs are defined in IEC61850-7-3 clause 7.
• Data objects (DO): Predefined names of objects associated with one or more logical nodes.
Their type or format is defined by one of the CDCs. They are listed only within the logical nodes. An example of a DO is “Auto” defined as CDC type SPS. It can be found in a number of logical nodes. Another example of a DO is “RHz” defined as an SPC (controllable single point), which is found only in the RSYN logical node.
Implementing IEC61850 in Equipment and Systems
• Logical nodes (LN): Predefined groupings of Data Objects that serve specific functions and
can be used to build the complete device. Examples of LNs include MMXU, which provides all electrical measurements in three-phase systems (voltage, current, watts, vars, or power factor), PTUV for the model of the voltage portion of under voltage protection, and XCBR for the short circuit breaking capability of a circuit breaker. These LNs are described in IEC61850-7-4 clause 5.
• Logical devices (LD): The device model composed of the relevant logical nodes. For
instance, a circuit breaker could be composed of the logical nodes XCBR, XSWI, CPOW, CSWI, and SMIG. Logical devices are not directly defined in any of the documents, because different products and different implementations can use different combinations of logical nodes for the same logical device. However, many examples are given in IEC61850-5. IEC61850 logical device servers (a server is a hardware device such as a computer) contain logical device models within them (a model is defined as software and database constructs which act as if they were the physical device they are modeling). These logical device models consist of one or more physical device models, along with some general information about device identity and global capabilities.
Physical device models, in turn, are constructed of multiple functional modules called logical nodes (LNs). Logical nodes are standard groupings of data objects that have been organized to serve a specific function. Therefore, a logical device server can be diagrammed as shown in Figure 6-4.
Implementing IEC61850 in Equipment and Systems
Figure 6-4
Example of the Relationship of Logical Device, Logical Nodes, Data Objects, and Common Data Classes
6.2.2.2 Object Model Naming
A critical aspect of IEC61850 is that every object has a unique name that is built from the object’s meaning, its type, its logical location, and its physical location. This uniqueness means that it is always clear exactly what an object is and where its value came from. It is similar to the concept of people having mailing addresses that indicate their name, their apartment number, their street address, their city, their state, and their country.
As illustrated in Figure 6-5, the IEC61850 object model names are built from some of the constructs described previously:
• Logical device (which also includes the name of the substation or other code for its physical
location)
Implementing IEC61850 in Equipment and Systems
Figure 6-5
IED Object Naming