GE Multilin PQM Instruction Manual page 126

A1 METERING
5–4
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sum of the phase currents does not equal 0, the result is the neutral current. When using
the CT input, the neutral current reading will be correct only if the CT is wired correctly and
the correct neutral CT primary value is entered. Verify neutral current by connecting a
clamp-on ammeter around all 3 phases. If the neutral current appears incorrect, check the
S2 SYSTEM SETUP \ CURRENT/VOLTAGE CONFIGURATION and verify the CT
settings in
wiring.
CURRENT UNBALANCE: Displays the percentage of current unbalance. Current unbalance
is calculated as:
I I
–
m av
-------------------- - × 100%
I
av
where:I = average phase current = (I
av
I = current in phase with maximum deviation from I
m
Even though it is possible to achieve unbalance greater than 100% with the
above formula, the PQM limits unbalance readings to 100%.
NOTE
If the average current is below 10% of the
forced to 0%. This avoids nuisance alarms when the system is lightly loaded. If the
simulation currents are being used, the unbalance is never forced to 0%.
Ia, Ib, Ic, In MINIMUM: Displays the minimum current magnitudes and the time and date of
their occurrence. This information is stored in non-volatile memory and is retained during
S1 PQM SETUP \ CLEAR DATA \ CLEAR MIN/MAX CURRENT
loss of control power. The
VALUES setpoint clears these values.
I U/B MINIMUM: Displays the minimum current unbalance and the time and date of its
measurement. This information is stored in non-volatile memory and is retained during
loss of control power. The S1 PQM SETUP \ CLEAR DATA \ CLEAR MIN/MAX CURRENT
VALUES setpoint clears this value.
Ia, Ib, Ic, In MAXIMUM: Displays the maximum current magnitudes and the time and date
of their occurrence. This information is stored in non-volatile memory and is retained
during loss of control power. The
CURRENT VALUES setpoint clears these values.
I U/B MAXIMUM: Displays the maximum current unbalance and the time and date of its
measurement. This information is stored in non-volatile memory and is retained during
loss of control power. The S1 PQM SETUP \ CLEAR DATA \ CLEAR MIN/MAX CURRENT
VALUES setpoint command clears this value.
+ I + I ) / 3
a b c
,
av
CT PRIMARY setpoint, the unbalance reading is
S1 PQM SETUP \ CLEAR DATA \ CLEAR MIN/MAX
PQM POWER QUALITY METER – INSTRUCTION MANUAL
CHAPTER 5: MONITORING