R.8.4
SEL-421 Relay Reference Manual Date Code 20111215
IEC 61850 Communications
IEC 61850 Operation
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. Tab le 8. 2 shows
how the A-phase current expressed as MMXU$A$phsA$cVal is broken down
into its component parts.
Data Mapping
Device data is mapped to IEC 61850 Logical Nodes (LN) according to rules
defined by SEL. Refer to IEC 61850-5:2003(E) and IEC 61850-7-4:2003(E)
for the mandatory content and usage of these LNs. The SEL-421 logical nodes
are grouped under Logical Devices for organization based on function. See
Tab le 8.3 for descriptions of the Logical Devices in an SEL-421. See Logical
Nodes on page R.8.16 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 become
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 the start, and why the IEC chose to
keep it for IEC 61850.
GOOSE
The Generic Object Oriented Substation Event (GOOSE) object within
IEC 61850 is for high-speed control messaging. IEC 61850 GOOSE
automatically broadcasts messages containing status, controls, and measured
values onto the network for use by other devices. IEC 61850 GOOSE sends
the message several times, increasing the likelihood that other devices receive
the messages.
IEC 61850 GOOSE objects can quickly and conveniently transfer status,
controls, and measured values between peers on an IEC 61850 network.
Configure SEL devices to respond to GOOSE messages from other network
devices with
ACSELERATOR Architect. Also, configure outgoing GOOSE
Table 8.2 Example IEC 61850 Descriptor Components
Component Description
MMXU Logical Node Polyphase measurement unit
A Data Object Phase-to-ground amperes
PhsA Sub-Data Object Phase A
CVal Data Attribute Complex value
Table 8.3 SEL-421 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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