R.4.4
SEL-421 Relay Reference Manual Date Code 20111215
Communications Interfaces
Communications Card
Severe power and ground problems
can occur on the communications
ports of this equipment as a result of
using non-SEL cables. Never use
standard null-modem cables with this
equipment.
You can connect to a standard 9-pin computer port with the SEL cable C234A
for relay configuration and programming with a terminal program or with the
ACSELERATOR QuickSet
®
SEL-5030 software. See Figure 2.41 on
page U.2.47 for the construction of SEL cable C234A.
Fiber-Optic Interface
You can add transceivers to the EIA-232 ports to use fiber-optic cables to
connect devices. We strongly recommend that you use fiber-optic cables to
connect devices within a substation. Power equipment and control circuit
switching can cause substantial interference with communications circuits.
You can also experience significant ground potential differences during fault
conditions that can interfere with communications and damage equipment.
Fiber-optic cables provide electrical isolation that increases safety and
equipment protection.
Use the SEL-2800 product family transceivers for multimode or single-mode
fiber-optic communications. All of these transceivers are port powered,
require no settings, and operate automatically over a broad range of data rates.
SEL-2800 series transceivers operate over the same wide temperature ranges
as SEL relays, providing reliable operations in extreme conditions.
EIA-485
There is no EIA-485 port integral to the SEL-421. You can install an
SEL-2885 or SEL-2884 transceiver to convert one of the rear-panel EIA-232
ports (PORT 1 or PORT 3) on the relay to an EIA-485 port. The SEL-2885 and
SEL-2884 are powered by the +5 Vdc output on Pin 1. These transceivers
offer transformer isolation not found on most EIA-232-to-EIA-485
transceivers. See the transceiver product flyers for more information. The
SEL-2885 offers the SEL distributed port switch (LMD) protocol. With this
protocol you can selectively communicate with multiple devices on an
EIA-485 network. You can communicate with other network nodes including
EIA-232 devices with an SEL-2885 and SEL devices having integral EIA-485
ports. You can find more information about using SEL LMD protocol in
Section 5: SEL Communications Protocols in the Reference Manual.
Communications Card
PORT 5 of the SEL-421 is a communications card slot. You can order the relay
with the card installed at the factory. The communications card slot provides
an interface to SEL-2700 series communications cards. As with other SEL
products, SEL has designed and tested SEL communications cards for
operation in harsh environments.
Ethernet Card
The optional Ethernet card provides Ethernet communications for the
SEL-421. The Ethernet card is available with standard twisted-pair and fiber-
optic physical interfaces. The Ethernet card includes redundant physical
interfaces with the capability to automatically transfer communications to the
backup interface in the event that the primary network fails. For information
on substation integration architectures, see SEL Communications
Processor Applications on page A.6.1, Direct Network Communication on
page A.7.1, Section 6: DNP3 Communications in the Reference Manual, and
Section 8: IEC 61850 Communications in the Reference Manual.
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