Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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7.3
Date Code 20171021 Instruction Manual SEL-421 Relay
Metering, Monitoring, and Reporting
Metering
Voltages, Currents, Frequency
NOTE:
After power up, automatic
restart, or a warm start, including
settings change and group switch, in
the beginning period of 20 cycles, the
10-cycle average values are initialized
with the latest calculated 1-cycle
average values.
Table 7.2 summarizes the metered voltage, current, and frequency quantities
available in the SEL-421. The relay reports all instantaneous voltage magnitudes,
current magnitudes, and frequency as absolute value 10-cycle averages (for
example, the LINE A-Phase filtered magnitude LIAFM_10c; see
Section 12:
Analog Quantities ). Instantaneous metering also reports sequence quantities ref-
erenced to A-Phase. The SEL-421 references angle measurements to positive-
sequence quantities. The relay reports angle measurements in the range of
±180.00 degrees.
Power
Table 7.3 shows the power quantities that the relay measures. The instantaneous
power measurements are derived from 10-cycle averages that the SEL-421
reports by using the generator condition of the positive power flow convention;
for example, real and reactive power flowing out (export) is positive, and real and
reactive power flowing in (import) is negative (see
Figure 7.1 ).
For power factor, LAG and LEAD refer to whether the current lags or leads the
applied voltage. The reactive power Q is positive when the voltage angle is
greater than the current angle (

V
>

I
), which is the case for inductive loads
Table 7.2 Instantaneous Metering Quantities—Voltages, Currents, Frequency
Metered Quantity Symbol Fundamental RMS
Phase voltage magnitude |V


X X
Phase voltage angle

(V

) X
Phase current magnitude |I

| X X
Phase current angle

(I

) X
Phase-to-phase voltage magnitude |V

| X X
Phase-to-phase voltage angle

(V

) X
Positive-sequence voltage magnitude |V
1
| X
Positive-sequence voltage angle

(V
1
) X
Negative-sequence voltage magnitude |3V
2
| X
Negative-sequence voltage angle

(3V
2
) X
Zero-sequence voltage magnitude |3V
0
| X
Zero-sequence voltage angle

(3V
0
) X
Positive-sequence current magnitude |I
1
| X
Positive-sequence current angle

(I
1
) X
Negative-sequence current magnitude |3I
2
| X
Negative-sequence current angle

(3I
2
) X
Zero-sequence current magnitude |3I
0
| X
Zero-sequence current angle

(3I
0
) X
Battery voltages Vdc X
Frequency f X X
Circuit breaker current magnitudes |I

| X X
Circuit breaker current angles

(I

) X