U.6.44
SEL-421 Relay User’s Guide Date Code 20090715
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.
Time/Date Errors
External IRIG time source error. Check IRIG-B time source or cables.
Check TIME Q command or
HMI SET/
SHOW | Date/Time
screen
1k PPS cable still connected. Remove 1k PPS cable (see Configuring
High-Accuracy Timekeeping on
page U.4.71)
IRIG-B connected to incorrect BNC input. Ensure that the correct BNC connector is
being used. See Figure 4.63 on
page U.4.74.
A low-priority time source error. Check last update source (TIME Q com-
mand or
HMI SET/SHOW | Date/Time
screen). See Table 4.9 on page U.4.71.
Lithium clock battery failure. Verify that the battery has failed before
replacing the battery—it should last for 10
years if the relay is energized. See Battery-
Backed Clock on page U.2.11.
Table 6.9 Troubleshooting Procedures (Sheet 3 of 3)
Possible Cause Diagnosis/Solution
Courtesy of NationalSwitchgear.com
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