U.6.40
SEL-421/SEL-421-1 Relay
User’s Guide
Date Code 20020501
Testing and Troubleshooting
Relay Troubleshooting
Relay Troubleshooting
Inspection
Procedure
Complete the following inspection procedure before disturbing the system.
After you finish the inspection, proceed to
Step 1. Confirm that the power is on. Do not turn the relay off.
Step 2. Measure and record the control power voltage at the relay
POWER terminals marked “+” and “–” on the rear-panel
terminal strip.
Step 3. Measure and record the voltages at all control inputs.
Step 4. Measure and record the state of all control outputs.
Step 5. Inspect the serial communications ports cabling to be sure that
a communications device is connected to at least one
communications port.
Troubleshooting
Procedures
Troubleshooting procedures for common problems are listed in
table lists each symptom, possible causes, and corresponding diagnoses/
solutions. Related SEL-421 Relay commands are listed in bold capitals. See
Section 8: ASCII Command Reference in the Reference Manual
for details on
SEL-421 Relay commands and
Section 9: Settings in the Reference Manual
for details on relay settings.
Table 6.9
Troubleshooting Procedures
(Sheet 1 of 3)
Possible Cause
Diagnosis/Solution
Dark Front Panel
Power is off.
Verify that substation battery power is
operational.
Input power is not present.
Verify that power is present at the rear-
panel terminal strip.
Blown power supply fuse.
Replace the fuse. See
Replacement on page U.2.39 in the User’s
Guide
Poor contrast adjustment.
Press and hold
{ESC}
for two seconds.
Press
{Up}
and
{Down}
pushbuttons to
adjust contrast.
Status Failure Notice on Front Panel
Self-test failure.
Contact the SEL factory or your Technical
Service Center.
The OUT108 relay control output b con-
tacts will be closed if you programmed
NOT HALARM to OUT108, see
Output on page U.2.42 in the User’s Guide
Alarm Output Asserts
Power is off.
Restore power.
Blown power supply fuse.
Replace the fuse. See
Replacement on page U.2.39 in the User’s
Guide
Power supply failure.
LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
Main board or interface board failure.
LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
Summary of Contents for SEL-421
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