GE PQM II - Page 143

CHAPTER 6: MONITORING
PQMII POWER QUALITY METER – INSTRUCTION MANUAL 6–5
• 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
a
+ I
b
+
I
c
= I
n
. If the 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 settings in
S2 SYSTEM SETUP ÖØ CURRENT/VOLTAGE
CONFIGURATION
and verify the CT wiring.
• CURRENT UNBALANCE: Displays the percentage of current unbalance. Current
unbalance is calculated as:
(EQ 0.1)
where:I
av
= average phase current = (I
a
+ I
b
+ I
c
) / 3
I
m
= current in phase with maximum deviation from I
av
,
Even though it is possible to achieve unbalance greater than 100% with the above
formula, the PQMII limits unbalance readings to 100%.
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 unbalance is never forced to 0%.
• Ia, Ib, Ic, In MIN: 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 PQMII SETUP ÖØ CLEAR DATA ÖØ CLEAR MIN/MAX CURRENT
VALUES setpoint clears these values.
• I U/B MIN: 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 PQMII SETUP ÖØ CLEAR DATA ÖØ CLEAR MIN/MAX CURRENT
VALUES setpoint clears this value.
• Ia, Ib, Ic, In MAX: 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 PQMII SETUP ÖØ CLEAR DATA ÖØ CLEAR MIN/MAX CURRENT
VALUES setpoint clears these values.
• I U/B MAX: 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 PQMII SETUP ÖØ CLEAR DATA ÖØ CLEAR MIN/MAX CURRENT
VALUES
setpoint command clears this value.
Current Unbalance
I
m
I
av
–
I
av
---------------------
100%×=