8.30
SEL-351A Relay Instruction Manual Date Code 20080213
Breaker Monitor and Metering
Maximum/Minimum Metering
(The factory default setting is set with time-overcurrent element pickups:
FAULT = 51P + 51G
If there is a fault, 51P or 51G asserts and blocks updating of maximum/
minimum metering values.)
In addition to FAULT being deasserted for at least 3600 cycles, the following
conditions must also be met:
➤ For wye-connected voltage values V
A,B,C,S
, or delta-connected
voltage values V
AB,BC,CA,S
, the voltage is above the threshold:
➢ 25.0 V secondary
➤ For current values I
A,B,C,N
the current is above the
corresponding threshold:
➢ 0.05 A secondary (5 A nominal current inputs)
➢ 0.01 A secondary (1 A nominal current inputs)
➢ 2.0 mA secondary (0.2 A nominal channel IN current
input)
➢ 0.5 mA secondary (0.05 A nominal channel IN current
input)
➤ For the residual current value I
G
:
➢ All three phase currents I
A,B,C
are above threshold.
➤ For power values MW
3P
and MVAR
3P
:
➢ All three phase currents I
A,B,C
are above threshold and
all three voltages V
A,B,C
(or V
AB,BC,CA
) are above
threshold.
➤ The metering value is above the previous maximum or below
the previous minimum for approximately four seconds.
The SEL-351A stores maximum/minimum values to nonvolatile storage once
per day and overwrites the previous stored value if that is exceeded. If the
relay loses control power, it will restore the maximum/minimum values saved
at 23:50 hours on the previous day.
NOTE: SELOGIC control equation
setting FAULT also controls other
relay functions; see SEL
OGIC Control
Equation Setting FAULT on page 5.13.
NOTE: The values used by the
maximum/minimum metering are the
same values used by the regular MET
command (serial port or
instantaneous, front panel), which are
eight-cycle averaged values. The
maximum/minimum metering
function updates every two seconds
(approximately). These values should
be relatively immune to transient
conditions.
In firmware releases R101 to R108,
inclusive, the maximum/minimum
metering values were based on high-
speed protection voltage values.
Because these values could update
after being above the previous
maximum or below the previous
minimum for only two cycles, the
maximum/minimum recorder
occasionally responded to transient
conditions. See Appendix A: Firmware
and Manual Versions for a list of
previous firmware releases.
Courtesy of NationalSwitchgear.com
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