7.7
Date Code 20171021 Instruction Manual SEL-421 Relay
Metering, Monitoring, and Reporting
Circuit Breaker Monitor
Synchrophasor Metering
The SEL-421 provides synchrophasor measurement with an angle reference
according to IEEE C37.118. See Section 7: Metering in the SEL-400 Series
Relays Instruction Manual for details of synchrophasor metering.
Circuit Breaker Monitor
The SEL-421 features advanced circuit breaker monitoring. The general features
of the circuit breaker monitor are described in Circuit Breaker Monitor on
page 8.1 in the SEL-400 Series Relays Instruction Manual. The SEL-421 sup-
ports monitoring of two breakers, designated 1 and 2.
Station DC Battery System Monitor
The SEL-421 automatically monitors station battery system health by measuring
the dc voltage, ac ripple, and voltage between each battery terminal and ground.
The relay provides two dc monitor channels, Vdc1 and Vdc2. See Station DC
Battery System Monitor on page 7.7 in the SEL-400 Series Relays Instruction
Manual for a complete description of the battery monitor.
Reporting
The SEL-421 features comprehensive power system data analysis capabilities,
which are described in Section 9: Reporting in the SEL-400 Series Relays
Instruction Manual. This section describes reporting characteristics that are
unique to the SEL-421.
Duration of Data Captures and Event Reports
The SEL-421 stores high-resolution raw data and filtered data. The number of
stored high-resolution raw data captures and event reports is a function of the
quantity of data contained in each capture.
Table 7.7 lists the maximum number of data captures/event reports the relay
stores in nonvolatile memory when ERDIG = S for various report lengths and
sample rates. The relay automatically overwrites the oldest events with the new-
est events when the nonvolatile storage capacity is exceeded.
NOTE: Consider the total capture
time when choosing a value for
setting LER at the SRATE := 8 kHz. At
LER := 3.0 the relay records at least 13
data captures when ERDIG = S. These
and smaller LER settings are sufficient
for most power system disturbances.
The relay stores high-resolution raw and filtered event data in nonvolatile mem-
ory. Table 7 .7 lists the storage capability of the SEL-421 for common event
reports.
The lower rows of Table 7 .7 show the number of event reports the relay stores at
the maximum data capture times for each SRATE sampling rate setting. Table
entries are the maximum number of stored events; these can vary by 10 percent
according to relay memory usage.
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