3-2 Installation Date Code 20010518
SEL-2020 Instruction Manual
alarm condition, and open for normal operation. This is a “Form B” contact because it is closed
when there is no power. To invert the alarm output to close under normal conditions, change
soldered jumper, JMP8, on the main board to select “Form A” contact usage. See Table 3.4 and
Figure 3.2 for jumper settings.
The alarm contact asserts when no power is connected to the SEL-2020, the power supply fails,
or self-test diagnostics detect a failure. Self-test diagnostic failures include memory failures,
power supply failures, and invalid settings failures. See STATUS command subsection in
Section 5: Commands for a discussion on these failures. If an I/O board is installed, the alarm
contact is pulsed when Level 2 communication is accessed, or when an SEL-2020 setting change
is accepted.
The ALARM LED will light whenever the alarm contact closes, unless there is a loss of power to
the LED.
IRIG-B Input Connection
The SEL-2020 accepts a modulated or demodulated IRIG-B signal through a rear panel BNC
connector labeled “MODULATED/DEMODULATED IRIG-B IN”. Three internal jumper
settings are required to identify which type of signal, modulated or demodulated, will be applied
to the SEL-2020. See Table 3.4 and Figure 3.2 for the main-board jumper positions to select the
appropriate type of IRIG-B input signal. The factory default setting is demodulated IRIG-B time
input.
Use a modulated IRIG-B signal for the input to the SEL-2020 if it is available. The modulated
signal is isolated by a transformer, and the demodulator in the SEL-2020 includes automatic gain
control. You can use a demodulated signal, but it may not be adequate if the cable to the source
is too long. A maximum cable length of 50 ft (15 meters) is recommended to ensure satisfactory
performance.
An internal element asserts in the SEL-2020 Global database region when an adequate IRIG-B
input signal is received. If no external IRIG-B input signal is applied, the SEL-2020 generates an
IRIG-B signal. The SEL-2020 includes an internal battery-backed clock/calendar that maintains
correct time with or without external power.
IRIG-B Output Connection
The SEL-2020 distributes a demodulated IRIG-B output signal through all of its 16 rear ports.
You can use this feature to synchronize any type of device, such as a relay, fault recorder, or
meter that can decode the IRIG-B signal: you need only to connect the device to the desired
SEL-2020 rear serial communication port using a special cable designed for both communication
and IRIG-B signal. The IRIG-B signal is on pins 4 and 6 of the 9-pin, subminiature “D”
connector (see Figure 3.1 and Table 3.1).
Where distance between the SEL-2020 and a device exceeds the cable length recommended for
conventional EIA-232 metallic conductor cables, you can use modems to provide isolation and to
establish communications to remote locations. Unfortunately, conventional short-haul, fiber
optic, and telephone modems do not support IRIG-B signal transmission, so their use requires
that you use some other method to synchronize the remote IED. Special fiber optic modems (like
the SEL-2810) are available, however, that include a channel for the IRIG-B time code; these
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