U.6.24
SEL-421/SEL-421-1 Relay
User’s Guide
Date Code 20020501
Testing and Troubleshooting
Checking Relay Operation
Checking Relay Operation
The SEL-421 Relay comes to you with all functions fully checked and
calibrated so that the relay operates correctly and accurately. You can perform
tests on the relay to verify proper relay operation, but you do not need to test
every relay element, timer, and function in this evaluation. The following
checks are valuable for confirming proper SEL-421 Relay connections and
operation:
➤
AC connection check (metering)
➤
Commissioning tests
➤
Functional tests
➤
Element verification
An ac connection check uses relay metering to verify that the relay current and
voltage inputs are the proper magnitude and phase rotation; see
Metering Quantities on page U.4.31 in the User’s Guide
. Commissioning tests
help you verify that you have properly connected the relay to the power
system and all auxiliary equipment. These tests confirm proper connection of
control inputs and control outputs as well; see
Operating the Relay Inputs and
Outputs on page U.4.52 in the User’s Guide
. Brief functional tests and
element verification confirm correct internal relay processing.
Selected
Element Tests
This subsection discusses tests of the following relay elements:
➤
Overcurrent element
➢
Negative-sequence instantaneous, 50Q1
➤
Directional element
➢
Negative-sequence portion, F32Q/R32Q, of the phase
directional element, F32P/R32P
➤
Distance element
➢
Phase-to-phase mho element, MBC2, of Zone 2 mho
distance element M2P
Testing
Overcurrent
Elements
Overcurrent elements operate by detecting power system sequence quantities
and asserting when these quantities exceed a preset threshold.
Apply current to the analog current inputs and compare relay operation to the
element pickup settings to test the instantaneous and definite-time overcurrent
elements. Be sure to apply the test current to the proper input set (IW or IX),
according to the Global Current and Voltage Source Selection settings (ESS
and ALINEI, for example) to accept the input. See
Source Selection on page R.1.2 in the Reference Manual
Phase Overcurrent Elements
The SEL-421 Relay phase overcurrent elements compare the phase current
applied to the secondary current inputs with the phase overcurrent element
pickup setting. The relay asserts the phase overcurrent elements when any of
the three phase currents exceeds the corresponding element pickup setting.
Summary of Contents for SEL-421
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