GE Power Quality Meter Series Instruction Manual page 117

5 MONITORING
NEUTRAL CURRENT: Neutral current can be determined by two methods. One method measures the current
via the neutral CT input. The second calculates the neutral current based on the three phase currents; using
the instantaneous samples, I
neutral current. When using the CT input, the neutral current reading will be correct only if the CT is wired cor-
rectly 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 settings in S2 SYSTEM SETUP \
CURRENT/VOLTAGE CONFIGURATION and verify the CT 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 CT PRIMARY setpoint, the unbalance reading is forced to 0%. This
avoids nuisance alarms when the system is lightly loaded. If the simulation currents are being used, the unbal-
ance 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 loss of control power. The
S1 PQM SETUP \ CLEAR DATA \ CLEAR MIN/MAX CURRENT 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
S1 PQM SETUP \ CLEAR DATA \ CLEAR MIN/MAX 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.
GE Power Management
+ I + I = I
. If the sum of the phase currents does not equal 0, the result is the
a b c n
+ I + I ) / 3
a b c
PQM Power Quality Meter
,
av
5.2 A1 METERING
5
5-3