Part 2 of a Data Modeling tutorial from Christoph Brunner, CEO of it4power.
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In the second part we will now introduce the various elements of the IEC 61850 Data Model. What are these elements? Some of the terms like logical devices, logical notes, data objects, or data attributes, you certainly have already heard about, but other terms are as well common data class and constructed attribute class. But what do they represent?
First of all, they are elements in a hierarchical data model that define within a 61850 server of an ID. The top level is the logical device. A logical device is a collection of logical nodes. The logical nodes contain data objects. And finally the structure of a data object is defined by the common data class. In the example, I and S is a common data class for status information. The common data class defines both data attributes are available for a data object. The data attribute are the leaves of the hierarchy. It is at the data attributes where we find the values. However data attributes can as well have a structure as a data type. In that case we have what we call a constructed attribute class shown here with the example "Quality."
Now that we have introduced these elements of the data model. I will explain for what they are used.
Let's start with a closer look at the logical node. Logical nodes are the key elements for modeling application functions. A logical nodes represents a functional element like a distant element of a protective function or the interface to a switch key equipment like a disconnecting switch. The logical nodes groups all the data that belongs to that function element. In our slide we see an extract of the logical node XSWI that represents the interface to an electrical switch as another circuit breaker. We have a first group of data objects defined here with the light blue background which is as an example a data object POS which represents the position of the switch. Or a data object block opening which represents that the block opening currently is blocked.
What we see as well is the indication M mandatory or O for optional with the particular data object needs to be present or not. The second group of data objects that we see in this example, which the light gray background a lot are data objects that are more used to control the behavior of the logical nodes and less for the specific semantic based on the logical node type.
Next, we introduce the data object and the data attributes. We use the example of the data object Pos, which represents the position of the switch from the previous logical node XSWI. This data object is of the common data class Double Point Control. A data object has multiple data attributes. The structure of the data object or with other words what data attributes are available is determined by the common data class.
We have a first group of data attributes representing the status information. Among them we have stVal where we find the value of the position of the switch which typically will be is or open or closed but can as well be in an intermediate or bad state. Then we have q for the quality indicating among other if the information is valid. And finally t for the timestamp of the last change of the position value.
These three attributes are the typical operational information of the switch position. But with the IEC 61850 Data Model we attach as well normal operational information. For example, configuration information to the same data object. Here we have a few examples like the possibility to describe the control behavior of the switch or the operate timeout. First we might have information related to substitution. Substitution will be described later. Also later we will discuss controls in IEC 61850 general and how to control parameters like the command to open or close the switch are modeled. Functional constraints are used to classify the data attributes based on their purpose.
In the example shown the functional constraint as t identifies the status attributes, c the configuration attributes, or sv the attributes related to substitution.
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