Date Code 20090715
User’s Guide
SEL-421 Relay
Section 6
U.User’s Guide
Testing and Troubleshooting
This section contains guidelines for determining and establishing test routines
for the SEL-421 Relay. Follow the standard practices of your company in
choosing testing philosophies, methods, and tools. The relay incorporates self-
tests to help you diagnose potential difficulties should these occur. The
subsection
Relay Troubleshooting on page U.6.42
contains a quick-reference
table for common relay operation problems.
Topics, tests, and troubleshooting procedures presented in this section include
the following:
➤
Testing Philosophy on page U.6.1
➤
Testing Features and Tools on page U.6.4
➤
Relay Test Connections on page U.6.8
➤
➤
Checking Relay Operation on page U.6.24
➤
Relay Self-Tests on page U.6.38
➤
Relay Troubleshooting on page U.6.42
➤
Factory Assistance on page U.6.45
The SEL-421 is factory calibrated; this section contains no calibration
information. If you suspect that the relay is out of calibration, contact your
Technical Service Center or the SEL factory.
Testing Philosophy
Protective relay testing generally consists of three categories: acceptance
testing, commissioning testing, and maintenance testing. The categories differ
in testing complexity and according to when these activities take place in the
life of the relay.
Each testing category includes particular details as to when to perform the test,
the testing goals at that time, and the relay functions that you need to test. This
information is a guide to testing the SEL-421; be sure to follow the practices
of your company for relay testing.
Acceptance Testing
SEL performs detailed acceptance testing on all new relay models and
versions. We are certain that your SEL-421 meets published specifications.
Even so, you can perform acceptance testing on a new relay model to become
familiar with the relay operating theory and settings; this familiarity helps you
apply the relay accurately and correctly. A summary of acceptance testing
guidelines is presented in
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