P.11.3
Date Code 20151029 Protection Manual SEL-411L Relay
Testing and Troubleshooting
Test Preca utions
You can use the relay reporting features as maintenance tools. Periodically
compare the relay METER command output to other meter readings on a line
to verify that the relay measures currents and voltages correctly and
accurately. Use the circuit breaker monitor, for example, to detect slow
breaker auxiliary contact operations and increasing or varying breaker pole
operating times. For details on these features, see Circuit Breaker Monitor on
page P.9.1.
Each occurrence of a fault tests the protection system and relay application.
Review relay event reports in detail after each fault to determine the areas
needing your attention. Use the event report current, voltage, and relay
element data to determine that the relay protection elements and
communications channels operate properly. Inspect event report input and
output data to determine whether the relay asserts outputs at the correct times
and whether auxiliary equipment operates properly.
At each maintenance interval, the only items to be tested are those that have
not operated (via fault conditions and otherwise) during the maintenance
interval. The basis for this testing philosophy is simple: you do not need to
perform further maintenance testing for a correctly set and connected relay
that measures the power system properly and for which no relay self-test has
failed.
The relay is based on microprocessor technology; the relay internal processing
characteristics do not change over time. For example, if time-overcurrent
element operating times change, these changes occur because of alterations to
relay settings and/or differences in the signals applied to the relay. You do not
need to verify relay element operating characteristics as a part of maintenance
checks.
SEL recommends that you limit maintenance tests on SEL relays according to
the guidelines listed in Table 11.3. You will spend less time checking relay
operations that function correctly. You can use the time you save to analyze
event data and thoroughly test systems needing more attention.
Test Precautions
Errors during testing can lead to unwanted operation of power equipment. The
default settings of the relay includes a Test Mode, which, when used in
conjunction with your company test procedures, allows protection functions to
be tested without the assertion of the output contacts.
The relay differential element is supervised by both local and remote
disturbance detectors. An operation of the differential element that occurs
without assertion of the disturbance detection logic and that resets before the
Table 11.3 Maintenance Testing
Details Description
Time Test at scheduled intervals or when there is an indication of a problem with the
relay or power system.
Goals a) Confirm that the relay is measuring ac quantities accurately.
b) Check that scheme logic and protection elements function correctly.
c) Verify that auxiliary equipment functions correctly.
Tests Test all relay features/power system components that did not operate during
an actual fault within the past maintenance interval.
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