An IEC 61850 data set is an ordered list of references to data or data attributes in a server. Client and server both know the list, so only its name and the values travel over the network. Report, log, GOOSE and sampled value control blocks use it to know what to send. It can come configured from the factory, be created persistently, or exist only for as long as one client's connection lasts.
What a data set is and what it is for
Short answer. A data set is an ordered list of references to data in a device. It groups what a communication mechanism is going to send, so that only the name of the list and the current values travel over the network.
IEC 61850-7-2 defines it as an ordered group of references to data or data attributes, the members, organized as a single collection for the client’s convenience. The key condition is that the order and the members are known to both client and server. With that condition, each message does not need to repeat names: it carries the identity of the set and the values in the agreed order. The standard presents this as a more efficient use of bandwidth.
A set does not contain data, it contains references. Each member points to a data object with its functional constraint (FCD) or to an attribute of that object with its functional constraint (FCDA). Members can belong to different logical nodes, and the same data can appear in several sets. For example, a circuit breaker position can be in the set that goes to SCADA by report and in the one another bay receives by GOOSE at the same time. For functional constraints, see the IEC 61850 overview.
Who uses data sets
Data sets are the common piece of the models that move information on events or cyclically:
| Mechanism | What it does with the set |
|---|---|
| Buffered and unbuffered reports | The control block watches the members and reports those that changed, or all of them, depending on the trigger |
| Log | Stores the values of the members in the device log when the conditions are met |
| GOOSE | Publishes the values of the members by multicast, with retransmission |
| Sampled values | The control block publishes in every message the values defined by the set |
| Direct read and write | A client reads or writes all the members with a single request |
The details of each mechanism are in IEC 61850 MMS, IEC 61850 GOOSE and sampled values. What matters here is that the content of the message is decided by the data set, not by the control block. Changing which signals reach SCADA or another bay is, almost always, changing a data set.
Three kinds of data set, by how they come to exist
The standard distinguishes how each instance exists, and that determines who sees it and how long it lasts:
- Configured. Defined in the device from its engineering. Clients on any connection see it and it cannot be deleted.
- Persistent. Created by a client with the create service and named with the path of the logical device, the logical node and the name of the set. Clients on any connection see it, and it is not deleted when the connection that created it ends. It can be deleted only if no enabled control block references it.
- Non-persistent. Identified by a name starting with ”@”. Only the client that created it sees it, and it is deleted automatically when that connection is released or drops. The standard limits its use to unbuffered reports and to sampled value control blocks with unicast transmission.
- Client creates the set. With the list of references to data and attributes
- Persistent or non-persistent?. Path with logical device and node, or a name with "@"
- Persistent. Visible to all clients; survives the connection that created it
- Non-persistent. Visible only to its creator; deleted when the connection closes
- Deletion. Only if no enabled control block uses it
Services to read, write and query
The services of the model are few, and all of them operate on the list, not on a single data object:
| Service | What it does |
|---|---|
| Get data set values | Returns the value of each member, or the reason for that member’s access error |
| Set data set values | Writes all the members and returns one result for each, in the order of the set |
| Create data set | Creates it with a list of references; fails if any member is not available to that client |
| Delete data set | Deletes it if the client has access |
| Get data set directory | Returns the list of references of the members |
For structured data, the read returns the values of all attributes at all levels. The responses depend on the client’s view: only the data visible to it is considered. That is why a service can work from an engineering tool and fail from another client on the same network.
How it maps to MMS
IEC 61850-8-1 maps each element to an MMS equivalent. The data set becomes a named variable list (NamedVariableList), and the services map to reading, writing, defining and deleting those lists and to querying their attributes. Persistent sets have server-wide or domain-wide scope, and non-persistent ones have association scope. To watch that traffic on the network, see IEC 61850 traffic analysis with Wireshark. To check the traffic on the network, Wireshark IEC 61850 gathers the capture and display filters for GOOSE, SV and MMS.
Changes and the revision number
Buffered reports and GOOSE carry a configuration revision count (ConfRev). In both cases the count increases when a member is removed from the data set or when the members are reordered. In GOOSE, changing the reference to the data set also counts. The value 0 is reserved, and a device restart must not reset it. The changes the standard considers for this counter are those made by local means, such as system configuration.
Another rule affects operation: changing the data set associated with a buffered report control block has the same effect as requesting a purge of its buffer, so pending events are discarded. In GOOSE, each member has a unique number starting at 1, which the standard calls MemberOffset; and if the data set exceeds the maximum number of values or size the mapping allows, the device flags that the block needs more configuration. How ICCP sends its data with transfer sets and report by exception is detailed in ICCP: Report by Exception and Transfer Sets.
The standard itself warns that a local reconfiguration of the members of a data set can cause unintended operations, and that the system must take measures to prevent unintended changes. Those measures, such as access control, are outside its scope.
What this means in practice
- When designing. Define data sets by purpose and by destination: one for what goes to SCADA, another for each GOOSE exchange. Mixing purposes means a change for one destination affects another.
- When integrating. The data set is described in the system configuration file; see SCL files and the SCL viewer to review it.
- When troubleshooting. If a report arrives without a signal, or a GOOSE stops being accepted after a modification, compare the order and members that the sender and receiver expect, and the configuration revision on each side. For a client that does not receive data, see IED not communicating over IEC 61850 MMS.
- When testing. Each signal must be followed to its destination with its quality and its timestamp; see point-to-point signal testing.
IEC 61850 data sets and configuration with Tiza Group
Do you need to review which signals each device delivers, or rebuild the reports and GOOSE of a substation? At Tiza Group we do the IEC 61850 engineering for your project and, if the device allows it, we review and adjust the configuration remotely through our remote relay configuration service, at medium, high and extra high voltage, in substations and industry. The origin of these services in UCA, created at EPRI, is told in UCA 2.0 and Its Relationship to IEC 61850.
Related guides
- IEC 61850: what it is, parts of the standard and data model
- IEC 61850 MMS: reports, SBO controls and files
- IEC 61850 GOOSE: messages between relays
- GOOSE and MMS in IEC 61850: differences and uses
- SCL files in IEC 61850
- Point-to-point signal testing
- Wireshark IEC 61850: Useful Capture and Display Filters
- UCA 2.0 and Its Relationship to IEC 61850
- ICCP: Report by Exception and Transfer Sets
References
- IEC 61850-7-2 (edition 1, 2003): clause 11, DATA-SET model; clauses 14 and 15, report, log and GOOSE control blocks.
- IEC 61850-8-1 (edition 1, 2004): clause 14, mapping of the data set model to MMS.
- IEC 61850-6 (edition 1, 2004): SCL DataSet element.
Frequently asked questions
Does a data set contain the data or only references to it?
Only references. The standard makes clear that the set does not contain the data: it holds a reference, with its functional constraint, to each data object or attribute, and those can belong to different logical nodes. The value is taken from the real data every time it is read, reported or published.
Why does the configuration revision number (ConfRev) of a GOOSE or report change?
Because the associated data set changed: a member was removed or the members were reordered. For GOOSE, changing the reference to the data set also counts. The receiver compares that number with the one it expects to detect that sender and receiver are no longer talking about the same list.
Can a client create its own data sets?
If the server allows it, the create service works in two ways: persistent, visible to all clients, or non-persistent, visible only to its creator and deleted when that connection closes. Non-persistent sets can only be used by unbuffered reports and by sampled values with unicast transmission. Sets configured in the device cannot be deleted.