ABB RELION 620 Series Technical Manual page 703

1MAC504801-IB E
8.4.4
620 series ANSI
Technical Manual
Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of the voltage unbalance power quality function can be described with a
module diagram. All the modules in the diagram are explained in the next sections.
V_A
V_B
V_C
Average
calculation
V
1
V
2
V
0
BLOCK
GUID-69B09FFB-8F8F-49AE-BEC7-42CB7272C224 V1 EN
Figure 352: Functional module diagram
Average calculation
PQVUB 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.
Power quality measurement functions
PCT_UNB_AL
Percentile
calculation
OBS_PR_ACT
MN_UNB_AL
Voltage
unbalance
detector
Recorded
data
Section 8
697