U.2.11
Date Code 20090715
User’s Guide
SEL-421 Relay
Installation
Shared Configuration Attributes
Every SEL-421 configuration includes the main board I/O and features these
connections:
➤
Three Hybrid (high-current-interrupting) Form A outputs
➤
Two Standard Form A outputs
➤
Three Standard Form C outputs
➤
Seven high-isolation control inputs (five independent and two
with a common leg)
TIME Inputs
The SEL-421 has a regular IRIG timekeeping mode, and a high-accuracy
IRIG (HIRIG) timekeeping mode, as described in
.
The IRIG-B serial data format consists of a 1-second frame containing 100
pulses divided into fields. The relay decodes the second, minute, hour, and day
fields and sets the internal time clock upon detecting valid time data in the
IRIG time mode.
There are two IRIG-B inputs on the SEL-421 rear panel, but only one is
capable of supporting the HIRIG mode. For input specifications, see
.
IRIG-B Pins of Serial Port 1
This IRIG-B input is capable of regular IRIG mode timekeeping only. Timing
accuracy for the IRIG time mode is 500 µs.
IRIG-B BNC Connector
This IRIG-B input is capable of both modes of timekeeping. If the connected
timekeeping source is qualified as high-accuracy (see
), the relay enters the HIRIG mode, which has a timing accuracy
of 1 µs.
If both inputs are connected, the SEL-421 will use the IRIG-B BNC connector
signal if a signal is detected.
SEL-421 Time Inputs Changed
If you are upgrading the firmware in an existing SEL-421 relay, you may need
to remove or reconnect your time-source cables. Beginning with the release of
SEL-421 firmware version R112, the rear-panel TIME inputs have been
changed. There is no longer a 1k PPS time input—see
for details.
Battery-Backed Clock
If relay input power is lost or removed, a lithium battery powers the relay
clock, providing date and time backup. The battery is a 3 V lithium coin cell,
Ray-O-Vac
®
No. BR2335 or equivalent. If power is lost or disconnected, the
battery discharges to power the clock. At room temperature (25°C), the battery
will operate for approximately 10 years at rated load.
When the SEL-421 is operating with power from an external source, the self-
discharge rate of the battery only is very small. Thus, battery life can extend
well beyond the nominal 10-year period because the battery rarely discharges
after the relay is installed. The battery cannot be recharged.
shows
the clock battery location (at the front of the main board).
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