F.4
SEL-751 Relay Instruction Manual Date Code 20170927
IEC 61850 Communications
IEC 61850 Operation
SEL communications processors (SEL-2032 and SEL-2030). Simply run an
MMS browser to query devices on an IEC 61850 network and discover what
data are available. Self-description also permits extensions to both standard
and custom data models. Instead of having to look up data in a profile stored
in its database, an IEC 61850 client can simply query an IEC 61850 device and
receive a description of all logical devices, logical nodes, and available data.
Unlike other Supervisory Control and Data Acquisition (SCADA) protocols
that present data as a list of addresses or indices, IEC 61850 presents data with
descriptors in a composite notation made up of components. Table F.2 shows
how the A-phase current expressed as MMXU$A$phsA$cVal is broken down
into its component parts.
Data Mapping
Device data are mapped to IEC 61850 logical nodes (LN) according to rules
SEL has defined. Refer to IEC 61850-5:2013(E) and IEC 61850-7-4:2010(E)
for the mandatory content and usage of these LNs. The SEL-751 logical nodes
are grouped under Logical Devices for organization based on function. See
Table F.3 for descriptions of the Logical Devices in an SEL-751. See Logical
Nodes for a description of the LNs that make up these Logical Devices.
MMS
Manufacturing Messaging Specification (MMS) provides services for the
application-layer transfer of real-time data within a substation LAN. MMS
was developed as a network independent data exchange protocol for industrial
networks in the 1980s and standardized as ISO 9506.
In theory, you can map IEC 61850 to any protocol. However, it can be
unwieldy and quite complicated to map objects and services to a protocol that
only provides access to simple data points via registers or index numbers.
MMS supports complex named objects and flexible services that enable
mapping to IEC 61850 in a straightforward manner. This was why the UCA
users group used MMS for UCA from that start, and why the IEC chose to
keep it for IEC 61850.
Table F.2 Example IEC 61850 Descriptor Components
Components Description
MMXU Logical Node Polyphase measurement unit
A Data Object Phase-to-ground amperes
PhsA Sub-Data Object A-phase
cVal Data Attribute Complex value
Table F.3 SEL-751 Logical Devices
Logical Device Description
ANN Annunciator elements—alarms, status values
CFG Configuration elements—datasets and report control blocks
CON Control elements—Remote bits
MET Metering or Measurement elements—currents, voltages, power, etc.
PRO Protection elements—protection functions and breaker control
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