P.9.30
SEL-411L Relay Protection Manual Date Code 20151029
Monitoring and Metering
Metering
Figure 9.16 Typical Current Measuring Accuracy
When you use Equation 9.7, you add an error amount related to the nominal
current rating of the relay, I
NOM
. Use just the numeric portion of I
NOM
, either
“5” for a 5 A relay or “1” for a 1 A relay; do not use the unit (A). The errors in
Example 9.11 are very small and qualify the relay as a high-accuracy meter.
Maximum/Minimum
Metering
The relay measures and retains the deviations of the power system since the
last maximum/minimum reset. Knowing these maximum and minimum
quantities can help you operate your power system more effectively in a
variety of ways. For example, you can benefit from maximum/minimum
metering information by using it to track power flow for troubleshooting,
planning future expansion, and scheduling maintenance.
The relay provides maximum/minimum metering for LINE input rms
voltages, 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 battery voltage maximums and minimums. The relay also records
the maximum values of the sequence voltages and sequence currents.
Table 9.17 lists these quantities.
Measured Current (A)
0.994
0.998
1.006
1.002
01.0
1.0
I
nom
= 5 A
Actual Value
Table 9.17 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
|
Frequency f
Circuit breaker rms current I
rms
Three-phase true real power 3P
rms
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