8.15
Date Code 20110408 Instruction Manual SEL-551 Relay
Testing and Troubleshooting
Maintenance Testing
Maintenance Testing
When: At regularly scheduled intervals, or when there is an indication of a
problem with the relay or system.
Goals:
➤ Ensure that the relay is measuring ac quantities accurately.
➤ Ensure that scheme logic and protection elements are
functioning correctly.
➤ Ensure that auxiliary equipment is functioning correctly.
What to test: Anything not shown to have operated during an actual fault
within the past maintenance interval.
SEL relays use extensive self-testing capabilities and feature detailed metering
and event reporting functions that lower the utility dependence on routine
maintenance testing.
Use the SEL relay reporting functions as maintenance tools.
1. Periodically verify that the relay is making correct and accurate
current measurements by comparing the relay METER output
to other meter readings on that line.
2. Review relay event reports in detail after each fault.
a. Using the event report current and relay element data,
you can determine that the relay protection elements are
operating properly.
b. Using the event report input and output data, you can
determine that the relay is asserting outputs at the
correct instants and that auxiliary equipment is
operating properly.
At the end of your maintenance interval, the only items that need testing are
those that have not operated during the maintenance interval.
The basis of this testing philosophy is simple: If the relay is correctly set and
connected, is measuring properly, and no self-test has failed, there is no reason
to test it further.
Each time a fault occurs, the protection system is tested. Use event report data
to determine areas requiring attention. Slow breaker auxiliary contact
operations and increasing or varying breaker operating time can be detected
through detailed analysis of relay event reports.
Because SEL relays are microprocessor-based, their operating characteristics
do not change over time. Time-overcurrent element operating times are
affected only by the relay settings and applied signals. It is not necessary to
verify operating characteristics as part of maintenance checks.
At SEL, we recommend that maintenance tests on SEL relays be limited under
the guidelines provided above. The time saved may be spent analyzing event
data and thoroughly testing those systems that require more attention.
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