U.2.43
Date Code 20090715 User’s Guide SEL-421 Relay
Installation
Connection
Optoisolated
Optoisolated control inputs are not polarity sensitive. These inputs respond to
voltage of either polarity, and can be used with ac control signals when
properly configured.
Note that the Main Board B I/O control inputs have one set of two inputs that
share a common input leg and INT3 and INT4 I/O interface boards have two
sets of nine inputs that share a common leg (see Figure 2.13).
Assigning
To assign the functions of the control inputs, see Operating the Relay Inputs
and Outputs on page U.4.56, or SET G on page R.9.41 for more details. You
can also use
ACSELERATOR QuickSet to set and verify operation of the inputs.
Control Outputs
The SEL-421 has three types of outputs:
➤ Standard outputs (example: main board OUT104)
➤ Hybrid (high-current-interrupting) outputs (example: main
board OUT101)
➤ Fast Hybrid (fast high-current-interrupting) outputs (example:
INT4 or INT5 (or INT8) board OUT201, or OUT301)
See Control Outputs on page U.2.7 for more information.
You can connect the Standard outputs and the Fast Hybrid (fast high-current-
interrupting) outputs in either ac or dc circuits. Connect the Hybrid (high-
current-interrupting) outputs to dc circuits only. The screw terminal connector
legends alert you about this requirement by showing polarity marks on the
Hybrid (high-current-interrupting) contacts.
Form A (SPST NO) contacts comprise the majority of the control outputs.
Two pairs of Form C (DPST CO) contacts are on the main board, the
INT1 (INT2) I/O interface board, and the INT6 (INT7) I/O interface board.
The INT4 and INT5 (INT8) I/O interface boards feature high-speed operation
capability using Fast Hybrid control outputs. To limit the false pickup
indications with digital inputs and light duty high-speed auxiliary relays,
precharging resistors are available on the screw terminal connector for each
pair of control output contacts for INT5 boards. See Fast Hybrid (Fast High-
Current-Interrupting) Control Outputs on page U.2.9 for further information,
and Figure 2.8 and Figure 2.9 for resistor connection details.
Alarm Output
The SEL-421 monitors internal processes and hardware in continual self-tests.
If the relay senses an out-of-tolerance condition, the relay declares a Status
Warning or a Status Failure. The relay signals a Status Warning by pulsing the
HALARM Relay Word bit (hardware alarm) to a logical 1 for five seconds.
For a Status Failure, the relay latches the HALARM Relay Word bit at
logical 1.
To provide remote alarm status indication, connect the b contact of OUT108
to your control system remote alarm input. Figure 2.40 shows the
configuration of the a and b contacts of control output OUT108.
Courtesy of NationalSwitchgear.com
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