5–6 PQM POWER QUALITY METER – INSTRUCTION MANUAL
A1 METERING CHAPTER 5: MONITORING
Iavg/Vavg: Displays the average of the three phase currents/voltages. This value is not
visible if the
VT WIRING setpoint is set to SINGLE PHASE DIRECT. L-N is displayed when VT
WIRING
is set to 4 WIRE WYE (3 VTs), 4 WIRE WYE DIRECT, 4 WIRE WYE (2 VTs), or 3 WIRE
DIRECT and L-L is displayed when
VT WIRING is set to 3 WIRE DELTA (2 VTs).
Vab, Vbc, Vca, VOLTAGE: Displays each line voltage corresponding to the A, B, and C
voltage inputs. The measured voltage is correct only if the
VT RATIO, VT NOMINAL
SECONDARY
, and VOLTAGE WIRING setpoints match the installed VTs. If the displayed
voltage does not match the actual voltage, check the setpoints and wiring.
AVERAGE LINE VOLTAGE: Displays the average of the three line voltages. This value is not
visible if the
VT WIRING setpoint is set to SINGLE PHASE DIRECT.
VOLTAGE UNBALANCE: Displays the percentage voltage unbalance. Voltage unbalance is
calculated as shown below. If the
VOLTAGE WIRING is configured for a WYE input, voltage
unbalance is calculated using phase quantities. If the
VT WIRING is configured as a DELTA
input, voltage unbalance is calculated using line voltages.
where:V
av
= average phase voltage = (V
an
+ V
bn
+ V
cn
) / 3 for WYE and 3 WIRE DIRECT
connections
= average line voltage (V
ab
+ V
bc
+ V
ca
) / 3 for 3 WIRE DELTA/2 VTs connection
V
m
= voltage in a phase (or line) with maximum deviation from V
av
,
Even though it is possible to achieve unbalance greater than 100% with the
above formula, the PQM will limit unbalance readings to 100%.
If the average voltage is below 10% of
VT RATIO × VT NOMINAL SECONDARY VOLTAGE
for 3 WIRE DELTA/2 VTs, 4 WIRE WYE/3 VTs, and 4 WIRE WYE/2 VTs connections, or below
10% of
VT RATIO × NOMINAL DIRECT INPUT VOLTAGE for 4 WIRE WYE/DIRECT and 3
WIRE DIRECT connections, the unbalance reading is forced to 0%. This is implemented to
avoid nuisance alarms when the system is lightly loaded. If the simulation voltages are
being used, the unbalance is never forced to 0%.
Van, Vbn, Vcn MINIMUM: Displays the minimum phase voltage 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 VOLTAGE VALUES
setpoint clears these values.
Vab, Vbc, Vca MINIMUM: Displays the minimum line voltage 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
VOLTAGE VALUES
setpoint clears these values.
V U/B MINIMUM: Displays minimum voltage 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. This value is cleared with the
S1 PQM SETUP \ CLEAR DATA \
CLEAR MIN/MAX VOLTAGE VALUES
setpoint.
V
m
V
av
–
V
av
------------------------
100%×
NOTE
Courtesy of NationalSwitchgear.com
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