R.8.3
Date Code 20111215 Reference Manual SEL-421 Relay
IEC 61850 Communications
IEC 61850 Operation
IEC 61850 Operation
Ethernet Networking
IEC 61850 and Ethernet networking model options are available when
ordering a new SEL-421 and may also be available as field upgrades to relays
equipped with the Ethernet card. In addition to IEC 61850, the Ethernet card
provides support protocols and data exchange, including FTP and Telnet, to
SEL devices. Access the SEL-421 Port 5 settings to configure all of the
Ethernet settings, including IEC 61850 network settings.
The SEL-421 Ethernet card supports IEC 61850 services, including transport
of Logical Node objects, over TCP/IP. The Ethernet card can coordinate a
maximum of six concurrent IEC 61850 sessions.
Object Models
The IEC 61850 standard relies heavily on the Abstract Communication
Service Interface (ACSI) models to define a set of services and the responses
to those services. In terms of network behavior, abstract modeling enables all
IEDs to act identically. These abstract models are used to create objects (data
items) and services that exist independently of any underlying protocols.
These objects are in conformance with the common data class (CDC)
specification IEC 61850-7-3, which describes the type and structure of each
element within a logical node. CDCs for status, measurements, controllable
analogs and statuses, and settings all have unique CDC attributes. Each CDC
attribute belongs to a set of functional constraints that groups the attributes
into specific categories such as status (ST), description (DC), and substituted
value (SV). Functional constraints, CDCs, and CDC attributes are used as
building blocks for defining Logical Nodes.
UCA2 used GOMSFE (Generic Object Models for Substation and Feeder
Equipment) to present data from station IEDs as a series of objects called
models or bricks. The IEC working group has incorporated GOMSFE
concepts into the standard, with some modifications to terminology; one
change was the renaming of bricks to logical nodes. Each logical node
represents a group of data (controls, status, measurements, etc.) associated
with a particular function. For example, the MMXU logical node (polyphase
measurement unit) contains measurement data and other points associated
with three-phase metering including voltages and currents. Each IED may
contain many functions such as protection, metering, and control. Multiple
logical nodes represent the functions in multifunction devices.
Logical nodes can be organized into logical devices that are similar to
directories on a computer disk. As represented in the IEC 61850 network,
each physical device can contain many logical devices and each logical device
can contain many logical nodes. Many relays, meters, and other IEC 61850
devices contain one primary logical device where all models are organized.
IEC 61850 devices are capable of self-description. You do not need to refer to
the specifications for the logical nodes, measurements, and other components
to request data from another IEC 61850 device. IEC 61850 clients can request
and display a list and description of the data available in an IEC 61850 server
device. This process is similar to the autoconfiguration process used within
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.
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