ABB RELION Series Technical Manual page 706

Section 10
Power quality measurement functions
700
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.
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.
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.
The activation of the BLOCK input blocks MN_UNB_AL output.
Percentile calculation
The Percentile calculation module performs the statistics calculation for the level of
voltage unbalance value for a settable duration. The operation of the Percentile
calculation module can be described with a module diagram.
1MRS758755 A
REC615 and RER615
Technical Manual