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7.6
SEL-421 Relay
Instruction Manual
Date Code 20171021
Metering, Monitoring, and Reporting
Metering
Demand Metering
Demand Metering on page 7.6 in the SEL-400 Series Relays Instruction
Manual
for a complete description of how demand metering works. The SEL-421
provides demand metering and peak demand metering for the LINE quantities.
lists the quantities used for demand and peak demand metering.
Energy Metering
Energy is the power consumed or developed in the electric power system mea-
sured over time. See
Energy Metering on page 7.6 in the SEL-400 Series Relays
Instruction Manual
for complete details of energy metering computation, view-
ing, and control. Energy metering is available only for the LINE data.
lists the energy metering quantities that the relay displays.
Frequency
f
Circuit breaker rms current
I
rms
Three-phase true real power
3P
rms
Three-phase reactive power
3Q
1
Three-phase true apparent power
3U
rms
a
Sequence components are maximum values only.
Table 7.4
Maximum/Minimum Metering Quantities—Voltages, Currents,
Frequency, and Powers (Sheet 2 of 2)
Metered Quantity
Symbol
Table 7.5
Demand and Peak Demand Metering Quantities—LINE
Symbol
Units
Description
I
rms
A, primary
Input rms current
I
Grms
a
a
(IG = 3I0 = IA + IB + IC).
A, primary
Residual ground rms current
3I
2
A, primary
Negative-sequence current
P
MW, primary
Single-phase real powers (with harmonics)
Q
MVAR, primary
Single-phase reactive powers
U
MVA, primary
Single-phase total powers (with harmonics)
3P
MW, primary
Three-phase real power (with harmonics)
3Q
MVAR, primary
Three-phase reactive power
3U
MVA, primary
Three-phase total power (with harmonics)
Table 7.6
Energy Metering Quantities—(LINE)
Analog Quantity
Units
Description
MWH
OUT
MWh, primary
Single-phase energy export
MWH
IN
MWh, primary
Single-phase energy import
MWH
T
MWh, primary
Single-phase energy total
3MWHOUT
MWh, primary
Three-phase energy export
3MWHIN
MWh, primary
Three-phase energy import
3MWH3T
MWh, primary
Three-phase energy total
Summary of Contents for SEL-421-4
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