Date Code 20171021 Instruction Manual SEL-421 Relay
Instruction ManualInstruction Manual
SECTION 7
Metering, Monitoring, and Reporting
The SEL-421 Relay provides extensive capabilities for monitoring substation
components, metering important power system parameters, and reporting on
power system performance. The relay provides the following useful features:
➤ Metering on page 7.1
➤ Circuit Breaker Monitor on page 7.7
➤ Station DC Battery System Monitor on page 7.7
➤ Reporting on page 7.7
See Section 7: Metering, Section 8: Monitoring, and Section 9: Reporting in the
SEL-400 Series Relays Instruction Manual for general information. This section
contains details specific to the SEL-421.
Metering
The SEL-421 provides five metering modes for measuring power system operations:
➤ Instantaneous Metering on page 7.2
➤ Maximum/Minimum Metering on page 7.5
➤ Demand Metering on page 7.6
➤ Energy Metering on page 7.6
➤ Synchrophasor Metering on page 7.7
Monitor present power system operating conditions with instantaneous metering.
Maximum/Minimum metering displays the largest and smallest system devia-
tions since the last reset. Demand metering includes either thermal or rolling
analyses of the power system and peak demand metering. Energy metering dis-
plays the megawatt-hours imported, megawatt-hours exported, and total mega-
watt-hours. Time-synchronized metering displays the line voltage and current
synchrophasors.
The SEL-421 processes three sets of current quantities: LINE, BK1, and BK2
(when configured for two circuit breakers). In one configuration using two circuit
breakers, Terminal W is usually connected as BK1, and Terminal X is generally
connected as BK2. The line voltage from Terminal Y (VY) provides the voltage
quantities for LINE. See Current and Voltage Source Selection on page 5.2 for
more information on configuring the SEL-421 inputs.
Use the MET command to access the metering functions. Issuing the MET com-
mand with no options returns the fundamental frequency measurement quantities
listed in Table 7.2. The MET command followed by a number, MET k, specifies
the number of times the command will repeat (k can range from 1 to 32767). This
is useful for troubleshooting or investigating uncharacteristic power system con-
ditions. With other command options, you can view currents from either circuit
breaker. For example, you can monitor the fundamental currents on Circuit
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