U.6.42
SEL-421/SEL-421-1 Relay User’s Guide Date Code 20020501
Testing and Troubleshooting
Relay Troubleshooting
Tripping Output Relay Remains Closed Following a Fault
Auxiliary contact control inputs are
improperly wired.
Check circuit breaker auxiliary contacts
wiring.
Control output relay contacts have burned
closed.
Remove relay power. Remove the control
output connection. Check continuity; ‘a’
contacts will be open and ‘b’ contacts will
be closed. Contact the SEL factory or your
Technical Service Center if continuity
checks fail.
I/O interface board failure. LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
Power Supply Voltage Status Warning
Power supply voltage(s) are out-of-toler-
ance.
Log the Status Warning. If repeated warn-
ings occur, take preventive action.
A/D converter failure. LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
Power Supply Voltage Status Failure
Power supply voltage(s) are
out-of-tolerance.
LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
A/D converter failure. LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
A/D OFFSET WARN Status Warning
Loose ribbon cable between the input mod-
ule board and the main board.
Reseat both ends of the analog input cable.
A/D converter drift. Log the Status Warning. If repeated warn-
ings occur, contact the SEL factory or your
Technical Service Center.
Master offset drift. LCD displays STATUS FAILURE screen.
Contact the SEL factory or your Technical
Service Center.
Table 6.9 Troubleshooting Procedures (Sheet 3 of 3)
Possible Cause Diagnosis/Solution
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