U3P
BLOCK
Average
calculation
U_A
Voltage
unbalance
detector
MN_UNB_AL
PCT_UNB_AL
OBS_PR_ACT
Percentile
calculation
Recorded
data
U_B
U_C
U
1
U
2
U
0
Figure 979: Functional module diagram
10.4.5.1 Average calculation
VSQVUB calculates two sets of measured voltage unbalance values, a three-second
and a ten-minute non-sliding average value. The three-second average value is used
for continuous monitoring. The ten-minute average is used for percentile calculation
for a longer period.
The Average calculation module uses five different methods for the average
calculation. The required method can be selected with the
Unb detection method
parameter.
When the "Neg Seq" mode is selected with
Unb detection method
, the voltage
unbalance is calculated based on the negative-sequence voltage magnitude.
Similarly, when the "Zero Seq" mode is selected, the voltage unbalance is calculated
based on the zero-sequence voltage magnitude. When the "Neg to Pos Seq" mode
is selected, the voltage unbalance is calculated based on the ratio of the negative-
sequence voltage magnitude to the positive-sequence magnitude. When the "Zero
to Pos Seq" mode is selected, the voltage unbalance is calculated based on the ratio
of the zero-sequence voltage magnitude to the positive-sequence magnitude. When
the "Ph vectors Comp" mode is selected, the ratio of the maximum phase voltage
magnitude deviation from the mean voltage magnitude to the mean of the phase
voltage magnitude is used for voltage unbalance calculation.
The calculated three-second value and ten-minute value are available in the
Monitored data view through the outputs 3S_MN_UNB and 10MN_MN_UNB.
3S_MN_UNB values are updated every three seconds and 10MIN_MN_UNB
is updated every minute.
For VT connection = "Delta", the calculated zero-sequence voltage is
always zero, hence, the setting
Unb detection method
= "Zero Seq" is
not applicable in this VT configuration.
10.4.5.2 Voltage unbalance detector
The three-second average value is calculated and compared to the set value
Unbalance start val
. If the voltage unbalance exceeds this limit, the MN_UNB_AL
output is activated.
Power quality measurement functions
1MRS759142 F
1850 REX640
Technical Manual
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