5.14
SEL-751 Relay Instruction Manual Date Code 20170927
Metering and Monitoring
Load Profiling
Small Signal Cutoff
for Metering
The relay applies a threshold to the voltage and current magnitude metering
quantities to force a reading to zero when the measurement is near zero. The
threshold for fundamental metering current values is 0.01 • I
NOM
A
(secondary) and for voltage values with 300 V inputs is 0.1 V (secondary) or
with 8 V LEA inputs is 0.0026 V (secondary). The threshold for rms metering
current values is 0.03 • I
NOM
A (secondary) and for voltage values with 300 V
inputs is 0.3 V (secondary) or with 8 V LEA inputs is 0.008 V (secondary).
The Global setting METHRES (Table 4.66) controls how these metering
functions work when the metered value is smaller than the previously stated
thresholds.
METHRES := Y
Set METHRES := Y to force the fundamental and rms metering values of
currents and voltages to zero when the corresponding applied signals fall
below the previously stated thresholds.
METHRES := N
Set METHRES := N to bypass the meter threshold checks and disable the
metering cutoff.
Load Profiling
The SEL-751 includes a load profiling function. The relay automatically
records selected quantities into nonvolatile memory every 5, 10, 15, 30, or 60
minutes, depending on the LDAR load profile report setting (see Load Profile
Settings on page 4.208). Choose which analog quantities you want to monitor
from the analog quantities listed in Appendix L: Analog Quantities. Set these
quantities into the LDLIST load profile list report setting.
The relay memory can hold data for 6500 time-stamped entries. For example,
if you choose to monitor 10 values at a rate of every 15 minutes, you could
store 66 days worth of data.
Use the serial port LDP command described in LDP Command (Load Profile
Report) to download the load rate profile data. See Figure 5.16 for an example
of an LDP serial port command response.
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