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U.4.2
SEL-421 Relay
User’s Guide
Date Code 20090715
Basic Relay Operations
Inspecting a New Relay
Initial Inspection
Perform the following initial inspection when the relay arrives:
Step 1. Remove the protective wrapping from the SEL-421.
Step 2. Observe the outside of the front cover and the rear panel.
Step 3. Check that no significant scratches or dents are evident on any
outer surface.
Step 4. Confirm that all terminal strips on the rear panel are secure.
Cleaning
Perform the following steps and use care when cleaning the SEL-421:
Step 1. Use a mild soap or detergent solution and a damp cloth to clean
the relay chassis.
Be careful cleaning the front and rear panels because a
permanent plastic sheet covers each panel; do not use abrasive
materials, polishing compounds, or harsh chemical solvents
(such as xylene or acetone) on any relay surface.
Step 2. Allow the relay to air dry, or wipe dry with a soft dry cloth.
Verify Relay
Configuration
When you first inspect the relay, confirm that the relay power supply voltage
and nominal ac signal magnitudes are appropriate for your application.
Examine the serial number label on the relay rear panel;
shows a
sample rear-panel serial number label.
Figure 4.1
SEL-421 Serial Number Label
shows a serial number label for an SEL-421 with additional I/O in a
5U horizontal chassis. This example serial number label is for a 5 A-per-phase
secondary current transformer input relay. For information on CT and PT
inputs, see
Secondary Circuits on page U.2.4
The serial number label does not list power system phase rotation and
frequency ratings, because you can use relay settings to configure these
parameters. The factory defaults are ABC phase rotation and 60 Hz nominal
frequency. See
Making Settings Changes: Initial Global Settings on
for details on setting these parameters.
The power supply specification in
indicates that this relay is
equipped with a power supply that accepts a nominal 48/125 Vdc input. This
power supply also accepts a 120 Vac input. Other power supply options
include nominal 24/48 Vdc and 125/250 Vdc power supplies. The 125/250
Vdc power supply also accepts a 120/230 Vac input. Refer to the serial
number label affixed to the back of your relay to determine the power supply
voltage you should apply to the relay power supply input terminals. As this
Part Number
Serial Number
Power Supply Input
Specifications
Secondary Voltage Input
Secondary Current Input
I/O Interface Board(s)
Logic Input Rating
(See Logic Input Ratings, below)
Summary of Contents for 421
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