Date Code 20111215 Reference Manual SEL-421 Relay
Section 4
R.Reference Manual
Communications Interfaces
This section provides information on communications interface options for
the SEL-421 Relay. The following topics are discussed:
➤ Communications Interfaces on page R.4.1
➤ Serial Communication on page R.4.2
➤ Communications Card on page R.4.4
Communications Interfaces
The SEL-421 collects, stores, and calculates a variety of data. These include
electrical power system measurements, calculated quantities, diagnostic data,
equipment monitoring data, fault oscillography, and sequential event reports.
You must enter settings to configure the SEL-421 to protect and monitor your
power system properly. A communications interface is the physical
connection on the relay that you can use to collect data from the relay, set the
relay, and perform relay test and diagnostic functions.
The SEL-421 has three rear-panel serial ports and one front-panel serial port.
These serial ports conform to the EIA/TIA-232 standard (often called
RS-232). Several optional SEL devices are available to provide alternative
physical interfaces, including EIA-485 and fiber-optic cable. The relay also
has a communications card slot for additional optional communications
interfaces including Ethernet.
Once you have established a physical connection, you must use a
communications protocol to interact with the relay. A communications
protocol is a language that you can use to perform relay operations and collect
data. For information on protocols that you can use with the SEL-421, see the
instruction manual sections listed in Table 4.1.
Table 4.1 SEL-421 Communications Protocols (Sheet 1 of 2)
Communications
Protocol
Communications Interface For More Information See
DNP3 (serial) EIA-232
a
Section 6: DNP3 Communi-
cations
DNP3 (LAN/WAN) Ethernet Card Section 6: DNP3 Communi-
cations
IEC 61850 Ethernet Card Section 8: IEC 61850 Com-
munications
Distributed Port Switch
(LMD)
SEL-2885 EIA-232 to
EIA-485 transceiver on an
EIA-232 port
Section 5: SEL Communi-
cations Protocols
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