Schweitzer Engineering Laboratories SEL-421-4 - Table 7.4 Maximum;Minimum Metering Quantities-Voltages, Currents, Frequency, and Powers

7.5
Date Code 20171021 Instruction Manual SEL-421 Relay
Metering, Monitoring, and Reporting
Metering
Relay Word bits PF_OK and DPF_OK are provided to indicate that the infor-
mation coming into the relay is sufficient to provide a valid power factor mea-
surement. The per-phase power factor bit, PF_OK, is equal to 1 if the measured
per-phase rms voltage, V
rms
, is greater than 10 percent of the nominal voltage
setting and the relay does not detect an open-phase condition. Otherwise,
PF_OK = 0. Similarly, for the per-phase displacement power factor check,
DPF_OK, is equal to 1 if the magnitude of the per-phase fundamental voltage,
VFM, is greater than 10 percent of the nominal voltage setting and the relay
does not detect an open-phase condition. Otherwise, DPF_OK = 0.
High-Accuracy Instantaneous Metering
The SEL-421 is a high-accuracy metering instrument. See Section 7: Metering in
the SEL-400 Series Relays Instruction Manual for details of the accuracy and
how to calculate error coefficients.
Maximum/Minimum Metering
See Maximum/Minimum Metering on page 7.5 in the SEL-400 Series Relays
Instruction Manual for a complete description of using and controlling maxi-
mum/minimum metering.
The SEL-421 provides maximum/minimum metering for LINE input rms volt-
ages, rms currents, rms powers, and frequency; it also conveys the maximum/
minimum rms currents for circuit breakers BK1 and BK2, as well as both dc bat-
tery voltage maximums and minimums. The SEL-421 also records the maximum
values of the sequence voltages and sequence currents. Table 7.4 lists these quan-
tities.
Three-phase true apparent power 3U
rms
X
Per-phase displacement power factor PF
1
X
Per-phase true power factor PF

X
Three-phase displacement power factor 3PF
1
X
Three-phase true power factor 3PF X
Table 7.3 Instantaneous Metering Quantities—Power (Sheet 2 of 2)
Metered Quantity Symbol
Fundamental
(50 Hz/
60 Hz Only)
RMS
(Harmonics
Included)
Table 7.4 Maximum/Minimum Metering Quantities—Voltages, Currents,
Frequency, and Powers (Sheet 1 of 2)
Metered Quantity Symbol
RMS phase voltage V
rms
RMS phase current I
rms
Positive-sequence voltage magnitude
a
|V
1
|
Negative-sequence voltage magnitude
a
|3V
2
|
Zero-sequence voltage magnitude
a
|3V
0
|
DC battery voltage VDC1, VDC2
Positive-sequence current magnitude
a
|I
1
|
Negative-sequence current magnitude
a
|3I
2
|
Zero-sequence current magnitude
a
|3I
0
|